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KVM: introduce readonly memslot

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In current code, if we map a readonly memory space from host to guest
and the page is not currently mapped in the host, we will get a fault
pfn and async is not allowed, then the vm will crash

We introduce readonly memory region to map ROM/ROMD to the guest, read access
is happy for readonly memslot, write access on readonly memslot will cause
KVM_EXIT_MMIO exit

Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
This commit is contained in:
Xiao Guangrong 2012-08-21 11:02:51 +08:00 committed by Avi Kivity
parent 7068d09715
commit 4d8b81abc4
7 changed files with 102 additions and 28 deletions
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10
Documentation/virtual/kvm/api.txt
View file

@ -857,7 +857,8 @@ struct kvm_userspace_memory_region {
};
/* for kvm_memory_region::flags */
#define KVM_MEM_LOG_DIRTY_PAGES 1UL
#define KVM_MEM_LOG_DIRTY_PAGES (1UL << 0)
#define KVM_MEM_READONLY (1UL << 1)
This ioctl allows the user to create or modify a guest physical memory
slot. When changing an existing slot, it may be moved in the guest
@ -873,9 +874,12 @@ It is recommended that the lower 21 bits of guest_phys_addr and userspace_addr
be identical. This allows large pages in the guest to be backed by large
pages in the host.
The flags field supports just one flag, KVM_MEM_LOG_DIRTY_PAGES, which
The flags field supports two flag, KVM_MEM_LOG_DIRTY_PAGES, which
instructs kvm to keep track of writes to memory within the slot. See
the KVM_GET_DIRTY_LOG ioctl.
the KVM_GET_DIRTY_LOG ioctl. Another flag is KVM_MEM_READONLY when the
KVM_CAP_READONLY_MEM capability, it indicates the guest memory is read-only,
that means, guest is only allowed to read it. Writes will be posted to
userspace as KVM_EXIT_MMIO exits.
When the KVM_CAP_SYNC_MMU capability, changes in the backing of the memory
region are automatically reflected into the guest. For example, an mmap()

1
arch/x86/include/asm/kvm.h
View file

@ -25,6 +25,7 @@
#define __KVM_HAVE_DEBUGREGS
#define __KVM_HAVE_XSAVE
#define __KVM_HAVE_XCRS
#define __KVM_HAVE_READONLY_MEM
/* Architectural interrupt line count. */
#define KVM_NR_INTERRUPTS 256

9
arch/x86/kvm/mmu.c
View file

@ -2647,6 +2647,15 @@ static void kvm_send_hwpoison_signal(unsigned long address, struct task_struct *
static int kvm_handle_bad_page(struct kvm_vcpu *vcpu, gfn_t gfn, pfn_t pfn)
{
/*
* Do not cache the mmio info caused by writing the readonly gfn
* into the spte otherwise read access on readonly gfn also can
* caused mmio page fault and treat it as mmio access.
* Return 1 to tell kvm to emulate it.
*/
if (pfn == KVM_PFN_ERR_RO_FAULT)
return 1;
if (pfn == KVM_PFN_ERR_HWPOISON) {
kvm_send_hwpoison_signal(gfn_to_hva(vcpu->kvm, gfn), current);
return 0;

1
arch/x86/kvm/x86.c
View file

@ -2175,6 +2175,7 @@ int kvm_dev_ioctl_check_extension(long ext)
case KVM_CAP_GET_TSC_KHZ:
case KVM_CAP_PCI_2_3:
case KVM_CAP_KVMCLOCK_CTRL:
case KVM_CAP_READONLY_MEM:
r = 1;
break;
case KVM_CAP_COALESCED_MMIO:

6
include/linux/kvm.h
View file

@ -106,7 +106,8 @@ struct kvm_userspace_memory_region {
* other bits are reserved for kvm internal use which are defined in
* include/linux/kvm_host.h.
*/
#define KVM_MEM_LOG_DIRTY_PAGES 1UL
#define KVM_MEM_LOG_DIRTY_PAGES (1UL << 0)
#define KVM_MEM_READONLY (1UL << 1)
/* for KVM_IRQ_LINE */
struct kvm_irq_level {
@ -621,6 +622,9 @@ struct kvm_ppc_smmu_info {
#define KVM_CAP_PPC_GET_SMMU_INFO 78
#define KVM_CAP_S390_COW 79
#define KVM_CAP_PPC_ALLOC_HTAB 80
#ifdef __KVM_HAVE_READONLY_MEM
#define KVM_CAP_READONLY_MEM 81
#endif
#ifdef KVM_CAP_IRQ_ROUTING

7
include/linux/kvm_host.h
View file

@ -465,6 +465,7 @@ int gfn_to_page_many_atomic(struct kvm *kvm, gfn_t gfn, struct page **pages,
struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn);
unsigned long gfn_to_hva(struct kvm *kvm, gfn_t gfn);
unsigned long gfn_to_hva_memslot(struct kvm_memory_slot *slot, gfn_t gfn);
void kvm_release_page_clean(struct page *page);
void kvm_release_page_dirty(struct page *page);
void kvm_set_page_dirty(struct page *page);
@ -792,12 +793,6 @@ hva_to_gfn_memslot(unsigned long hva, struct kvm_memory_slot *slot)
return slot->base_gfn + gfn_offset;
}
static inline unsigned long gfn_to_hva_memslot(struct kvm_memory_slot *slot,
gfn_t gfn)
{
return slot->userspace_addr + (gfn - slot->base_gfn) * PAGE_SIZE;
}
static inline gpa_t gfn_to_gpa(gfn_t gfn)
{
return (gpa_t)gfn << PAGE_SHIFT;

96
virt/kvm/kvm_main.c
View file

@ -680,7 +680,13 @@ void update_memslots(struct kvm_memslots *slots, struct kvm_memory_slot *new)
static int check_memory_region_flags(struct kvm_userspace_memory_region *mem)
{
if (mem->flags & ~KVM_MEM_LOG_DIRTY_PAGES)
u32 valid_flags = KVM_MEM_LOG_DIRTY_PAGES;
#ifdef KVM_CAP_READONLY_MEM
valid_flags |= KVM_MEM_READONLY;
#endif
if (mem->flags & ~valid_flags)
return -EINVAL;
return 0;
@ -973,18 +979,45 @@ unsigned long kvm_host_page_size(struct kvm *kvm, gfn_t gfn)
return size;
}
static unsigned long gfn_to_hva_many(struct kvm_memory_slot *slot, gfn_t gfn,
gfn_t *nr_pages)
static bool memslot_is_readonly(struct kvm_memory_slot *slot)
{
return slot->flags & KVM_MEM_READONLY;
}
static unsigned long __gfn_to_hva_memslot(struct kvm_memory_slot *slot,
gfn_t gfn)
{
return slot->userspace_addr + (gfn - slot->base_gfn) * PAGE_SIZE;
}
static unsigned long __gfn_to_hva_many(struct kvm_memory_slot *slot, gfn_t gfn,
gfn_t *nr_pages, bool write)
{
if (!slot || slot->flags & KVM_MEMSLOT_INVALID)
return KVM_HVA_ERR_BAD;
if (memslot_is_readonly(slot) && write)
return KVM_HVA_ERR_RO_BAD;
if (nr_pages)
*nr_pages = slot->npages - (gfn - slot->base_gfn);
return gfn_to_hva_memslot(slot, gfn);
return __gfn_to_hva_memslot(slot, gfn);
}
static unsigned long gfn_to_hva_many(struct kvm_memory_slot *slot, gfn_t gfn,
gfn_t *nr_pages)
{
return __gfn_to_hva_many(slot, gfn, nr_pages, true);
}
unsigned long gfn_to_hva_memslot(struct kvm_memory_slot *slot,
gfn_t gfn)
{
return gfn_to_hva_many(slot, gfn, NULL);
}
EXPORT_SYMBOL_GPL(gfn_to_hva_memslot);
unsigned long gfn_to_hva(struct kvm *kvm, gfn_t gfn)
{
return gfn_to_hva_many(gfn_to_memslot(kvm, gfn), gfn, NULL);
@ -997,7 +1030,7 @@ EXPORT_SYMBOL_GPL(gfn_to_hva);
*/
static unsigned long gfn_to_hva_read(struct kvm *kvm, gfn_t gfn)
{
return gfn_to_hva_many(gfn_to_memslot(kvm, gfn), gfn, NULL);
return __gfn_to_hva_many(gfn_to_memslot(kvm, gfn), gfn, NULL, false);
}
static int kvm_read_hva(void *data, void __user *hva, int len)
@ -1106,6 +1139,17 @@ static int hva_to_pfn_slow(unsigned long addr, bool *async, bool write_fault,
return npages;
}
static bool vma_is_valid(struct vm_area_struct *vma, bool write_fault)
{
if (unlikely(!(vma->vm_flags & VM_READ)))
return false;
if (write_fault && (unlikely(!(vma->vm_flags & VM_WRITE))))
return false;
return true;
}
/*
* Pin guest page in memory and return its pfn.
* @addr: host virtual address which maps memory to the guest
@ -1130,8 +1174,6 @@ static pfn_t hva_to_pfn(unsigned long addr, bool atomic, bool *async,
/* we can do it either atomically or asynchronously, not both */
BUG_ON(atomic && async);
BUG_ON(!write_fault && !writable);
if (hva_to_pfn_fast(addr, atomic, async, write_fault, writable, &pfn))
return pfn;
@ -1158,7 +1200,7 @@ static pfn_t hva_to_pfn(unsigned long addr, bool atomic, bool *async,
vma->vm_pgoff;
BUG_ON(!kvm_is_mmio_pfn(pfn));
} else {
if (async && (vma->vm_flags & VM_WRITE))
if (async && vma_is_valid(vma, write_fault))
*async = true;
pfn = KVM_PFN_ERR_FAULT;
}
@ -1167,19 +1209,40 @@ static pfn_t hva_to_pfn(unsigned long addr, bool atomic, bool *async,
return pfn;
}
static pfn_t
__gfn_to_pfn_memslot(struct kvm_memory_slot *slot, gfn_t gfn, bool atomic,
bool *async, bool write_fault, bool *writable)
{
unsigned long addr = __gfn_to_hva_many(slot, gfn, NULL, write_fault);
if (addr == KVM_HVA_ERR_RO_BAD)
return KVM_PFN_ERR_RO_FAULT;
if (kvm_is_error_hva(addr))
return KVM_PFN_ERR_BAD;
/* Do not map writable pfn in the readonly memslot. */
if (writable && memslot_is_readonly(slot)) {
*writable = false;
writable = NULL;
}
return hva_to_pfn(addr, atomic, async, write_fault,
writable);
}
static pfn_t __gfn_to_pfn(struct kvm *kvm, gfn_t gfn, bool atomic, bool *async,
bool write_fault, bool *writable)
{
unsigned long addr;
struct kvm_memory_slot *slot;
if (async)
*async = false;
addr = gfn_to_hva(kvm, gfn);
if (kvm_is_error_hva(addr))
return KVM_PFN_ERR_BAD;
slot = gfn_to_memslot(kvm, gfn);
return hva_to_pfn(addr, atomic, async, write_fault, writable);
return __gfn_to_pfn_memslot(slot, gfn, atomic, async, write_fault,
writable);
}
pfn_t gfn_to_pfn_atomic(struct kvm *kvm, gfn_t gfn)
@ -1210,15 +1273,12 @@ EXPORT_SYMBOL_GPL(gfn_to_pfn_prot);
pfn_t gfn_to_pfn_memslot(struct kvm_memory_slot *slot, gfn_t gfn)
{
unsigned long addr = gfn_to_hva_memslot(slot, gfn);
return hva_to_pfn(addr, false, NULL, true, NULL);
return __gfn_to_pfn_memslot(slot, gfn, false, NULL, true, NULL);
}
pfn_t gfn_to_pfn_memslot_atomic(struct kvm_memory_slot *slot, gfn_t gfn)
{
unsigned long addr = gfn_to_hva_memslot(slot, gfn);
return hva_to_pfn(addr, true, NULL, true, NULL);
return __gfn_to_pfn_memslot(slot, gfn, true, NULL, true, NULL);
}
EXPORT_SYMBOL_GPL(gfn_to_pfn_memslot_atomic);