lguest: use a special 1:1 linear pagetable mode until first switch.
The Host used to create some page tables for the Guest to use at the
top of Guest memory; it would then tell the Guest where this was. In
particular, it created linear mappings for 0 and 0xC0000000 addresses
because lguest used to switch to its real page tables quite late in
boot.
However, since d50d8fe19 Linux initialized boot page tables in
head_32.S even before the "are we lguest?" boot jump. So, now we can
simplify things: the Host pagetable code assumes 1:1 linear mapping
until it first calls the LHCALL_NEW_PGTABLE hypercall, which we now do
before we reach C code.
This also means that the Host doesn't need to know anything about the
Guest's PAGE_OFFSET. (Non-Linux guests might not even have such a
thing).
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Rusty Russell
parent
e0377e2520
commit
5dea1c88ed
6 changed files with 98 additions and 205 deletions
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@ -63,7 +63,6 @@ void foo(void)
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BLANK();
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OFFSET(LGUEST_DATA_irq_enabled, lguest_data, irq_enabled);
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OFFSET(LGUEST_DATA_irq_pending, lguest_data, irq_pending);
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OFFSET(LGUEST_DATA_pgdir, lguest_data, pgdir);
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BLANK();
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OFFSET(LGUEST_PAGES_host_gdt_desc, lguest_pages, state.host_gdt_desc);
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@ -520,17 +520,16 @@ static unsigned long lguest_read_cr2(void)
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/* See lguest_set_pte() below. */
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static bool cr3_changed = false;
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static unsigned long current_cr3;
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/*
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* cr3 is the current toplevel pagetable page: the principle is the same as
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* cr0. Keep a local copy, and tell the Host when it changes. The only
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* difference is that our local copy is in lguest_data because the Host needs
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* to set it upon our initial hypercall.
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* cr0. Keep a local copy, and tell the Host when it changes.
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*/
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static void lguest_write_cr3(unsigned long cr3)
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{
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lguest_data.pgdir = cr3;
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lazy_hcall1(LHCALL_NEW_PGTABLE, cr3);
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current_cr3 = cr3;
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/* These two page tables are simple, linear, and used during boot */
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if (cr3 != __pa(swapper_pg_dir) && cr3 != __pa(initial_page_table))
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@ -539,7 +538,7 @@ static void lguest_write_cr3(unsigned long cr3)
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static unsigned long lguest_read_cr3(void)
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{
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return lguest_data.pgdir;
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return current_cr3;
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}
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/* cr4 is used to enable and disable PGE, but we don't care. */
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@ -758,7 +757,7 @@ static void lguest_pmd_clear(pmd_t *pmdp)
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static void lguest_flush_tlb_single(unsigned long addr)
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{
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/* Simply set it to zero: if it was not, it will fault back in. */
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lazy_hcall3(LHCALL_SET_PTE, lguest_data.pgdir, addr, 0);
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lazy_hcall3(LHCALL_SET_PTE, current_cr3, addr, 0);
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}
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/*
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@ -27,13 +27,18 @@
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.section .init.text, "ax", @progbits
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ENTRY(lguest_entry)
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/*
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* We make the "initialization" hypercall now to tell the Host about
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* us, and also find out where it put our page tables.
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* We make the "initialization" hypercall now to tell the Host where
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* our lguest_data struct is.
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*/
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movl $LHCALL_LGUEST_INIT, %eax
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movl $lguest_data - __PAGE_OFFSET, %ebx
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int $LGUEST_TRAP_ENTRY
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/* Now turn our pagetables on; setup by arch/x86/kernel/head_32.S. */
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movl $LHCALL_NEW_PGTABLE, %eax
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movl $(initial_page_table - __PAGE_OFFSET), %ebx
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int $LGUEST_TRAP_ENTRY
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/* Set up the initial stack so we can run C code. */
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movl $(init_thread_union+THREAD_SIZE),%esp
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@ -59,6 +59,8 @@ struct lg_cpu {
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struct lguest_pages *last_pages;
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/* Initialization mode: linear map everything. */
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bool linear_pages;
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int cpu_pgd; /* Which pgd this cpu is currently using */
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/* If a hypercall was asked for, this points to the arguments. */
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@ -17,7 +17,6 @@
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#include <linux/percpu.h>
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#include <asm/tlbflush.h>
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#include <asm/uaccess.h>
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#include <asm/bootparam.h>
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#include "lg.h"
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/*M:008
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@ -325,10 +324,15 @@ bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
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#endif
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/* First step: get the top-level Guest page table entry. */
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gpgd = lgread(cpu, gpgd_addr(cpu, vaddr), pgd_t);
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/* Toplevel not present? We can't map it in. */
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if (!(pgd_flags(gpgd) & _PAGE_PRESENT))
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return false;
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if (unlikely(cpu->linear_pages)) {
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/* Faking up a linear mapping. */
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gpgd = __pgd(CHECK_GPGD_MASK);
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} else {
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gpgd = lgread(cpu, gpgd_addr(cpu, vaddr), pgd_t);
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/* Toplevel not present? We can't map it in. */
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if (!(pgd_flags(gpgd) & _PAGE_PRESENT))
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return false;
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}
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/* Now look at the matching shadow entry. */
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spgd = spgd_addr(cpu, cpu->cpu_pgd, vaddr);
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@ -353,10 +357,15 @@ bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
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}
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#ifdef CONFIG_X86_PAE
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gpmd = lgread(cpu, gpmd_addr(gpgd, vaddr), pmd_t);
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/* Middle level not present? We can't map it in. */
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if (!(pmd_flags(gpmd) & _PAGE_PRESENT))
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return false;
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if (unlikely(cpu->linear_pages)) {
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/* Faking up a linear mapping. */
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gpmd = __pmd(_PAGE_TABLE);
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} else {
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gpmd = lgread(cpu, gpmd_addr(gpgd, vaddr), pmd_t);
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/* Middle level not present? We can't map it in. */
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if (!(pmd_flags(gpmd) & _PAGE_PRESENT))
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return false;
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}
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/* Now look at the matching shadow entry. */
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spmd = spmd_addr(cpu, *spgd, vaddr);
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@ -397,8 +406,13 @@ bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
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gpte_ptr = gpte_addr(cpu, gpgd, vaddr);
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#endif
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/* Read the actual PTE value. */
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gpte = lgread(cpu, gpte_ptr, pte_t);
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if (unlikely(cpu->linear_pages)) {
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/* Linear? Make up a PTE which points to same page. */
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gpte = __pte((vaddr & PAGE_MASK) | _PAGE_RW | _PAGE_PRESENT);
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} else {
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/* Read the actual PTE value. */
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gpte = lgread(cpu, gpte_ptr, pte_t);
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}
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/* If this page isn't in the Guest page tables, we can't page it in. */
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if (!(pte_flags(gpte) & _PAGE_PRESENT))
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@ -454,7 +468,8 @@ bool demand_page(struct lg_cpu *cpu, unsigned long vaddr, int errcode)
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* Finally, we write the Guest PTE entry back: we've set the
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* _PAGE_ACCESSED and maybe the _PAGE_DIRTY flags.
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*/
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lgwrite(cpu, gpte_ptr, pte_t, gpte);
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if (likely(!cpu->linear_pages))
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lgwrite(cpu, gpte_ptr, pte_t, gpte);
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/*
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* The fault is fixed, the page table is populated, the mapping
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@ -612,6 +627,11 @@ unsigned long guest_pa(struct lg_cpu *cpu, unsigned long vaddr)
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#ifdef CONFIG_X86_PAE
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pmd_t gpmd;
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#endif
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/* Still not set up? Just map 1:1. */
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if (unlikely(cpu->linear_pages))
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return vaddr;
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/* First step: get the top-level Guest page table entry. */
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gpgd = lgread(cpu, gpgd_addr(cpu, vaddr), pgd_t);
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/* Toplevel not present? We can't map it in. */
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@ -708,32 +728,6 @@ static unsigned int new_pgdir(struct lg_cpu *cpu,
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return next;
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}
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/*H:430
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* (iv) Switching page tables
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*
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* Now we've seen all the page table setting and manipulation, let's see
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* what happens when the Guest changes page tables (ie. changes the top-level
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* pgdir). This occurs on almost every context switch.
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*/
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void guest_new_pagetable(struct lg_cpu *cpu, unsigned long pgtable)
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{
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int newpgdir, repin = 0;
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/* Look to see if we have this one already. */
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newpgdir = find_pgdir(cpu->lg, pgtable);
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/*
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* If not, we allocate or mug an existing one: if it's a fresh one,
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* repin gets set to 1.
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*/
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if (newpgdir == ARRAY_SIZE(cpu->lg->pgdirs))
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newpgdir = new_pgdir(cpu, pgtable, &repin);
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/* Change the current pgd index to the new one. */
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cpu->cpu_pgd = newpgdir;
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/* If it was completely blank, we map in the Guest kernel stack */
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if (repin)
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pin_stack_pages(cpu);
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}
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/*H:470
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* Finally, a routine which throws away everything: all PGD entries in all
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* the shadow page tables, including the Guest's kernel mappings. This is used
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@ -780,6 +774,44 @@ void guest_pagetable_clear_all(struct lg_cpu *cpu)
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/* We need the Guest kernel stack mapped again. */
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pin_stack_pages(cpu);
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}
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/*H:430
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* (iv) Switching page tables
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*
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* Now we've seen all the page table setting and manipulation, let's see
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* what happens when the Guest changes page tables (ie. changes the top-level
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* pgdir). This occurs on almost every context switch.
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*/
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void guest_new_pagetable(struct lg_cpu *cpu, unsigned long pgtable)
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{
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int newpgdir, repin = 0;
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/*
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* The very first time they call this, we're actually running without
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* any page tables; we've been making it up. Throw them away now.
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*/
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if (unlikely(cpu->linear_pages)) {
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release_all_pagetables(cpu->lg);
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cpu->linear_pages = false;
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/* Force allocation of a new pgdir. */
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newpgdir = ARRAY_SIZE(cpu->lg->pgdirs);
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} else {
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/* Look to see if we have this one already. */
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newpgdir = find_pgdir(cpu->lg, pgtable);
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}
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/*
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* If not, we allocate or mug an existing one: if it's a fresh one,
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* repin gets set to 1.
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*/
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if (newpgdir == ARRAY_SIZE(cpu->lg->pgdirs))
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newpgdir = new_pgdir(cpu, pgtable, &repin);
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/* Change the current pgd index to the new one. */
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cpu->cpu_pgd = newpgdir;
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/* If it was completely blank, we map in the Guest kernel stack */
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if (repin)
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pin_stack_pages(cpu);
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}
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/*:*/
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/*M:009
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@ -919,168 +951,26 @@ void guest_set_pmd(struct lguest *lg, unsigned long pmdp, u32 idx)
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}
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#endif
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/*H:505
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* To get through boot, we construct simple identity page mappings (which
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* set virtual == physical) and linear mappings which will get the Guest far
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* enough into the boot to create its own. The linear mapping means we
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* simplify the Guest boot, but it makes assumptions about their PAGE_OFFSET,
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* as you'll see.
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*
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* We lay them out of the way, just below the initrd (which is why we need to
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* know its size here).
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*/
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static unsigned long setup_pagetables(struct lguest *lg,
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unsigned long mem,
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unsigned long initrd_size)
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{
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pgd_t __user *pgdir;
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pte_t __user *linear;
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unsigned long mem_base = (unsigned long)lg->mem_base;
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unsigned int mapped_pages, i, linear_pages;
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#ifdef CONFIG_X86_PAE
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pmd_t __user *pmds;
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unsigned int j;
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pgd_t pgd;
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pmd_t pmd;
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#else
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unsigned int phys_linear;
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#endif
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/*
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* We have mapped_pages frames to map, so we need linear_pages page
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* tables to map them.
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*/
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mapped_pages = mem / PAGE_SIZE;
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linear_pages = (mapped_pages + PTRS_PER_PTE - 1) / PTRS_PER_PTE;
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/* We put the toplevel page directory page at the top of memory. */
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pgdir = (pgd_t *)(mem + mem_base - initrd_size - PAGE_SIZE);
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/* Now we use the next linear_pages pages as pte pages */
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linear = (void *)pgdir - linear_pages * PAGE_SIZE;
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#ifdef CONFIG_X86_PAE
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/*
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* And the single mid page goes below that. We only use one, but
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* that's enough to map 1G, which definitely gets us through boot.
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*/
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pmds = (void *)linear - PAGE_SIZE;
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#endif
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/*
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* Linear mapping is easy: put every page's address into the
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* mapping in order.
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*/
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for (i = 0; i < mapped_pages; i++) {
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pte_t pte;
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pte = pfn_pte(i, __pgprot(_PAGE_PRESENT|_PAGE_RW|_PAGE_USER));
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if (copy_to_user(&linear[i], &pte, sizeof(pte)) != 0)
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return -EFAULT;
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}
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#ifdef CONFIG_X86_PAE
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/*
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* Make the Guest PMD entries point to the corresponding place in the
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* linear mapping (up to one page worth of PMD).
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*/
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for (i = j = 0; i < mapped_pages && j < PTRS_PER_PMD;
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i += PTRS_PER_PTE, j++) {
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pmd = pfn_pmd(((unsigned long)&linear[i] - mem_base)/PAGE_SIZE,
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__pgprot(_PAGE_PRESENT | _PAGE_RW | _PAGE_USER));
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if (copy_to_user(&pmds[j], &pmd, sizeof(pmd)) != 0)
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return -EFAULT;
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}
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/* One PGD entry, pointing to that PMD page. */
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pgd = __pgd(((unsigned long)pmds - mem_base) | _PAGE_PRESENT);
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/* Copy it in as the first PGD entry (ie. addresses 0-1G). */
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if (copy_to_user(&pgdir[0], &pgd, sizeof(pgd)) != 0)
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return -EFAULT;
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/*
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* And the other PGD entry to make the linear mapping at PAGE_OFFSET
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*/
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if (copy_to_user(&pgdir[KERNEL_PGD_BOUNDARY], &pgd, sizeof(pgd)))
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return -EFAULT;
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#else
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/*
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* The top level points to the linear page table pages above.
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* We setup the identity and linear mappings here.
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*/
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phys_linear = (unsigned long)linear - mem_base;
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for (i = 0; i < mapped_pages; i += PTRS_PER_PTE) {
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pgd_t pgd;
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/*
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* Create a PGD entry which points to the right part of the
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* linear PTE pages.
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*/
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pgd = __pgd((phys_linear + i * sizeof(pte_t)) |
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(_PAGE_PRESENT | _PAGE_RW | _PAGE_USER));
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/*
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* Copy it into the PGD page at 0 and PAGE_OFFSET.
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*/
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if (copy_to_user(&pgdir[i / PTRS_PER_PTE], &pgd, sizeof(pgd))
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|| copy_to_user(&pgdir[pgd_index(PAGE_OFFSET)
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+ i / PTRS_PER_PTE],
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&pgd, sizeof(pgd)))
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return -EFAULT;
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}
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#endif
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/*
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* We return the top level (guest-physical) address: we remember where
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* this is to write it into lguest_data when the Guest initializes.
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*/
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return (unsigned long)pgdir - mem_base;
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}
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/*H:500
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* (vii) Setting up the page tables initially.
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*
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* When a Guest is first created, the Launcher tells us where the toplevel of
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* its first page table is. We set some things up here:
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* When a Guest is first created, set initialize a shadow page table which
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* we will populate on future faults. The Guest doesn't have any actual
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* pagetables yet, so we set linear_pages to tell demand_page() to fake it
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* for the moment.
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*/
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int init_guest_pagetable(struct lguest *lg)
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{
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u64 mem;
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u32 initrd_size;
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struct boot_params __user *boot = (struct boot_params *)lg->mem_base;
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#ifdef CONFIG_X86_PAE
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pgd_t *pgd;
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pmd_t *pmd_table;
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#endif
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/*
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* Get the Guest memory size and the ramdisk size from the boot header
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* located at lg->mem_base (Guest address 0).
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||||
*/
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if (copy_from_user(&mem, &boot->e820_map[0].size, sizeof(mem))
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|| get_user(initrd_size, &boot->hdr.ramdisk_size))
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return -EFAULT;
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struct lg_cpu *cpu = &lg->cpus[0];
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int allocated = 0;
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/*
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* We start on the first shadow page table, and give it a blank PGD
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* page.
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*/
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lg->pgdirs[0].gpgdir = setup_pagetables(lg, mem, initrd_size);
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if (IS_ERR_VALUE(lg->pgdirs[0].gpgdir))
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return lg->pgdirs[0].gpgdir;
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lg->pgdirs[0].pgdir = (pgd_t *)get_zeroed_page(GFP_KERNEL);
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if (!lg->pgdirs[0].pgdir)
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/* lg (and lg->cpus[]) starts zeroed: this allocates a new pgdir */
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cpu->cpu_pgd = new_pgdir(cpu, 0, &allocated);
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if (!allocated)
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return -ENOMEM;
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#ifdef CONFIG_X86_PAE
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/* For PAE, we also create the initial mid-level. */
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pgd = lg->pgdirs[0].pgdir;
|
||||
pmd_table = (pmd_t *) get_zeroed_page(GFP_KERNEL);
|
||||
if (!pmd_table)
|
||||
return -ENOMEM;
|
||||
|
||||
set_pgd(pgd + SWITCHER_PGD_INDEX,
|
||||
__pgd(__pa(pmd_table) | _PAGE_PRESENT));
|
||||
#endif
|
||||
|
||||
/* This is the current page table. */
|
||||
lg->cpus[0].cpu_pgd = 0;
|
||||
/* We start with a linear mapping until the initialize. */
|
||||
cpu->linear_pages = true;
|
||||
return 0;
|
||||
}
|
||||
|
||||
|
|
@ -1095,10 +985,10 @@ void page_table_guest_data_init(struct lg_cpu *cpu)
|
|||
* of virtual addresses used by the Switcher.
|
||||
*/
|
||||
|| put_user(RESERVE_MEM * 1024 * 1024,
|
||||
&cpu->lg->lguest_data->reserve_mem)
|
||||
|| put_user(cpu->lg->pgdirs[0].gpgdir,
|
||||
&cpu->lg->lguest_data->pgdir))
|
||||
&cpu->lg->lguest_data->reserve_mem)) {
|
||||
kill_guest(cpu, "bad guest page %p", cpu->lg->lguest_data);
|
||||
return;
|
||||
}
|
||||
|
||||
/*
|
||||
* In flush_user_mappings() we loop from 0 to
|
||||
|
|
|
|||
|
|
@ -59,8 +59,6 @@ struct lguest_data {
|
|||
unsigned long reserve_mem;
|
||||
/* KHz for the TSC clock. */
|
||||
u32 tsc_khz;
|
||||
/* Page where the top-level pagetable is */
|
||||
unsigned long pgdir;
|
||||
|
||||
/* Fields initialized by the Guest at boot: */
|
||||
/* Instruction range to suppress interrupts even if enabled */
|
||||
|
|
|
|||
Loading…
Reference in a new issue