kernel-fxtec-pro1x/arch/x86/lguest/i386_head.S

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#include <linux/linkage.h>
#include <linux/lguest.h>
#include <asm/lguest_hcall.h>
#include <asm/asm-offsets.h>
#include <asm/thread_info.h>
#include <asm/processor-flags.h>
#include <asm/pgtable.h>
/*G:020
* Our story starts with the kernel booting into startup_32 in
* arch/x86/kernel/head_32.S. It expects a boot header, which is created by
* the bootloader (the Launcher in our case).
*
* The startup_32 function does very little: it clears the uninitialized global
* C variables which we expect to be zero (ie. BSS) and then copies the boot
* header and kernel command line somewhere safe. Finally it checks the
* 'hardware_subarch' field. This was introduced in 2.6.24 for lguest and Xen:
* if it's set to '1' (lguest's assigned number), then it calls us here.
*
* WARNING: be very careful here! We're running at addresses equal to physical
* addesses (around 0), not above PAGE_OFFSET as most code expectes
* (eg. 0xC0000000). Jumps are relative, so they're OK, but we can't touch any
* data without remembering to subtract __PAGE_OFFSET!
*
* The .section line puts this code in .init.text so it will be discarded after
* boot.
*/
.section .init.text, "ax", @progbits
ENTRY(lguest_entry)
/*
* We make the "initialization" hypercall now to tell the Host about
* us, and also find out where it put our page tables.
*/
movl $LHCALL_LGUEST_INIT, %eax
movl $lguest_data - __PAGE_OFFSET, %ebx
int $LGUEST_TRAP_ENTRY
/* Set up the initial stack so we can run C code. */
movl $(init_thread_union+THREAD_SIZE),%esp
call init_pagetables
/* Jumps are relative: we're running __PAGE_OFFSET too low. */
jmp lguest_init+__PAGE_OFFSET
/*
* Initialize page tables. This creates a PDE and a set of page
* tables, which are located immediately beyond __brk_base. The variable
* _brk_end is set up to point to the first "safe" location.
* Mappings are created both at virtual address 0 (identity mapping)
* and PAGE_OFFSET for up to _end.
*
* FIXME: This code is taken verbatim from arch/x86/kernel/head_32.S: they
* don't have a stack at this point, so we can't just use call and ret.
*/
init_pagetables:
#if PTRS_PER_PMD > 1
#define PAGE_TABLE_SIZE(pages) (((pages) / PTRS_PER_PMD) + PTRS_PER_PGD)
#else
#define PAGE_TABLE_SIZE(pages) ((pages) / PTRS_PER_PGD)
#endif
#define pa(X) ((X) - __PAGE_OFFSET)
/* Enough space to fit pagetables for the low memory linear map */
MAPPING_BEYOND_END = \
PAGE_TABLE_SIZE(((1<<32) - __PAGE_OFFSET) >> PAGE_SHIFT) << PAGE_SHIFT
#ifdef CONFIG_X86_PAE
/*
* In PAE mode initial_page_table is statically defined to contain
* enough entries to cover the VMSPLIT option (that is the top 1, 2 or 3
* entries). The identity mapping is handled by pointing two PGD entries
* to the first kernel PMD.
*
* Note the upper half of each PMD or PTE are always zero at this stage.
*/
#define KPMDS (((-__PAGE_OFFSET) >> 30) & 3) /* Number of kernel PMDs */
xorl %ebx,%ebx /* %ebx is kept at zero */
movl $pa(__brk_base), %edi
movl $pa(initial_pg_pmd), %edx
movl $PTE_IDENT_ATTR, %eax
10:
leal PDE_IDENT_ATTR(%edi),%ecx /* Create PMD entry */
movl %ecx,(%edx) /* Store PMD entry */
/* Upper half already zero */
addl $8,%edx
movl $512,%ecx
11:
stosl
xchgl %eax,%ebx
stosl
xchgl %eax,%ebx
addl $0x1000,%eax
loop 11b
/*
* End condition: we must map up to the end + MAPPING_BEYOND_END.
*/
movl $pa(_end) + MAPPING_BEYOND_END + PTE_IDENT_ATTR, %ebp
cmpl %ebp,%eax
jb 10b
1:
addl $__PAGE_OFFSET, %edi
movl %edi, pa(_brk_end)
shrl $12, %eax
movl %eax, pa(max_pfn_mapped)
/* Do early initialization of the fixmap area */
movl $pa(initial_pg_fixmap)+PDE_IDENT_ATTR,%eax
movl %eax,pa(initial_pg_pmd+0x1000*KPMDS-8)
#else /* Not PAE */
page_pde_offset = (__PAGE_OFFSET >> 20);
movl $pa(__brk_base), %edi
movl $pa(initial_page_table), %edx
movl $PTE_IDENT_ATTR, %eax
10:
leal PDE_IDENT_ATTR(%edi),%ecx /* Create PDE entry */
movl %ecx,(%edx) /* Store identity PDE entry */
movl %ecx,page_pde_offset(%edx) /* Store kernel PDE entry */
addl $4,%edx
movl $1024, %ecx
11:
stosl
addl $0x1000,%eax
loop 11b
/*
* End condition: we must map up to the end + MAPPING_BEYOND_END.
*/
movl $pa(_end) + MAPPING_BEYOND_END + PTE_IDENT_ATTR, %ebp
cmpl %ebp,%eax
jb 10b
addl $__PAGE_OFFSET, %edi
movl %edi, pa(_brk_end)
shrl $12, %eax
movl %eax, pa(max_pfn_mapped)
/* Do early initialization of the fixmap area */
movl $pa(initial_pg_fixmap)+PDE_IDENT_ATTR,%eax
movl %eax,pa(initial_page_table+0xffc)
#endif
ret
/*G:055
* We create a macro which puts the assembler code between lgstart_ and lgend_
* markers. These templates are put in the .text section: they can't be
* discarded after boot as we may need to patch modules, too.
*/
.text
#define LGUEST_PATCH(name, insns...) \
lgstart_##name: insns; lgend_##name:; \
.globl lgstart_##name; .globl lgend_##name
LGUEST_PATCH(cli, movl $0, lguest_data+LGUEST_DATA_irq_enabled)
LGUEST_PATCH(pushf, movl lguest_data+LGUEST_DATA_irq_enabled, %eax)
/*G:033
* But using those wrappers is inefficient (we'll see why that doesn't matter
* for save_fl and irq_disable later). If we write our routines carefully in
* assembler, we can avoid clobbering any registers and avoid jumping through
* the wrapper functions.
*
* I skipped over our first piece of assembler, but this one is worth studying
* in a bit more detail so I'll describe in easy stages. First, the routine to
* enable interrupts:
*/
ENTRY(lg_irq_enable)
/*
* The reverse of irq_disable, this sets lguest_data.irq_enabled to
* X86_EFLAGS_IF (ie. "Interrupts enabled").
*/
movl $X86_EFLAGS_IF, lguest_data+LGUEST_DATA_irq_enabled
/*
* But now we need to check if the Host wants to know: there might have
* been interrupts waiting to be delivered, in which case it will have
* set lguest_data.irq_pending to X86_EFLAGS_IF. If it's not zero, we
* jump to send_interrupts, otherwise we're done.
*/
testl $0, lguest_data+LGUEST_DATA_irq_pending
jnz send_interrupts
/*
* One cool thing about x86 is that you can do many things without using
* a register. In this case, the normal path hasn't needed to save or
* restore any registers at all!
*/
ret
send_interrupts:
/*
* OK, now we need a register: eax is used for the hypercall number,
* which is LHCALL_SEND_INTERRUPTS.
*
* We used not to bother with this pending detection at all, which was
* much simpler. Sooner or later the Host would realize it had to
* send us an interrupt. But that turns out to make performance 7
* times worse on a simple tcp benchmark. So now we do this the hard
* way.
*/
pushl %eax
movl $LHCALL_SEND_INTERRUPTS, %eax
/*
* This is a vmcall instruction (same thing that KVM uses). Older
* assembler versions might not know the "vmcall" instruction, so we
* create one manually here.
*/
.byte 0x0f,0x01,0xc1 /* KVM_HYPERCALL */
/* Put eax back the way we found it. */
popl %eax
ret
/*
* Finally, the "popf" or "restore flags" routine. The %eax register holds the
* flags (in practice, either X86_EFLAGS_IF or 0): if it's X86_EFLAGS_IF we're
* enabling interrupts again, if it's 0 we're leaving them off.
*/
ENTRY(lg_restore_fl)
/* This is just "lguest_data.irq_enabled = flags;" */
movl %eax, lguest_data+LGUEST_DATA_irq_enabled
/*
* Now, if the %eax value has enabled interrupts and
* lguest_data.irq_pending is set, we want to tell the Host so it can
* deliver any outstanding interrupts. Fortunately, both values will
* be X86_EFLAGS_IF (ie. 512) in that case, and the "testl"
* instruction will AND them together for us. If both are set, we
* jump to send_interrupts.
*/
testl lguest_data+LGUEST_DATA_irq_pending, %eax
jnz send_interrupts
/* Again, the normal path has used no extra registers. Clever, huh? */
ret
/*:*/
/* These demark the EIP range where host should never deliver interrupts. */
.global lguest_noirq_start
.global lguest_noirq_end
/*M:004
* When the Host reflects a trap or injects an interrupt into the Guest, it
* sets the eflags interrupt bit on the stack based on lguest_data.irq_enabled,
* so the Guest iret logic does the right thing when restoring it. However,
* when the Host sets the Guest up for direct traps, such as system calls, the
* processor is the one to push eflags onto the stack, and the interrupt bit
* will be 1 (in reality, interrupts are always enabled in the Guest).
*
* This turns out to be harmless: the only trap which should happen under Linux
* with interrupts disabled is Page Fault (due to our lazy mapping of vmalloc
* regions), which has to be reflected through the Host anyway. If another
* trap *does* go off when interrupts are disabled, the Guest will panic, and
* we'll never get to this iret!
:*/
/*G:045
* There is one final paravirt_op that the Guest implements, and glancing at it
* you can see why I left it to last. It's *cool*! It's in *assembler*!
*
* The "iret" instruction is used to return from an interrupt or trap. The
* stack looks like this:
* old address
* old code segment & privilege level
* old processor flags ("eflags")
*
* The "iret" instruction pops those values off the stack and restores them all
* at once. The only problem is that eflags includes the Interrupt Flag which
* the Guest can't change: the CPU will simply ignore it when we do an "iret".
* So we have to copy eflags from the stack to lguest_data.irq_enabled before
* we do the "iret".
*
* There are two problems with this: firstly, we need to use a register to do
* the copy and secondly, the whole thing needs to be atomic. The first
* problem is easy to solve: push %eax on the stack so we can use it, and then
* restore it at the end just before the real "iret".
*
* The second is harder: copying eflags to lguest_data.irq_enabled will turn
* interrupts on before we're finished, so we could be interrupted before we
* return to userspace or wherever. Our solution to this is to surround the
* code with lguest_noirq_start: and lguest_noirq_end: labels. We tell the
* Host that it is *never* to interrupt us there, even if interrupts seem to be
* enabled.
*/
ENTRY(lguest_iret)
pushl %eax
movl 12(%esp), %eax
lguest_noirq_start:
/*
* Note the %ss: segment prefix here. Normal data accesses use the
* "ds" segment, but that will have already been restored for whatever
* we're returning to (such as userspace): we can't trust it. The %ss:
* prefix makes sure we use the stack segment, which is still valid.
*/
movl %eax,%ss:lguest_data+LGUEST_DATA_irq_enabled
popl %eax
iret
lguest_noirq_end: