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KVM: x86: improve reexecute_instruction 

The current reexecute_instruction can not well detect the failed instruction
emulation. It allows guest to retry all the instructions except it accesses
on error pfn

For example, some cases are nested-write-protect - if the page we want to
write is used as PDE but it chains to itself. Under this case, we should
stop the emulation and report the case to userspace

Reviewed-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
This commit is contained in:
Xiao Guangrong 2013-01-13 23:49:07 +08:00 committed by Marcelo Tosatti
parent 95b3cf69bd
commit 93c05d3ef2
3 changed files with 45 additions and 11 deletions
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7
arch/x86/include/asm/kvm_host.h
View File

@ -497,6 +497,13 @@ struct kvm_vcpu_arch {
u64 msr_val;
struct gfn_to_hva_cache data;
} pv_eoi;
/*
* Indicate whether the access faults on its page table in guest
* which is set when fix page fault and used to detect unhandeable
* instruction.
*/
bool write_fault_to_shadow_pgtable;
};
struct kvm_lpage_info {

27
arch/x86/kvm/paging_tmpl.h
View File

@ -497,26 +497,34 @@ out_gpte_changed:
* created when kvm establishes shadow page table that stop kvm using large
* page size. Do it early can avoid unnecessary #PF and emulation.
*
* @write_fault_to_shadow_pgtable will return true if the fault gfn is
* currently used as its page table.
*
* Note: the PDPT page table is not checked for PAE-32 bit guest. It is ok
* since the PDPT is always shadowed, that means, we can not use large page
* size to map the gfn which is used as PDPT.
*/
static bool
FNAME(is_self_change_mapping)(struct kvm_vcpu *vcpu,
struct guest_walker *walker, int user_fault)
struct guest_walker *walker, int user_fault,
bool *write_fault_to_shadow_pgtable)
{
int level;
gfn_t mask = ~(KVM_PAGES_PER_HPAGE(walker->level) - 1);
bool self_changed = false;
if (!(walker->pte_access & ACC_WRITE_MASK ||
(!is_write_protection(vcpu) && !user_fault)))
return false;
for (level = walker->level; level <= walker->max_level; level++)
if (!((walker->gfn ^ walker->table_gfn[level - 1]) & mask))
return true;
for (level = walker->level; level <= walker->max_level; level++) {
gfn_t gfn = walker->gfn ^ walker->table_gfn[level - 1];
return false;
self_changed |= !(gfn & mask);
*write_fault_to_shadow_pgtable |= !gfn;
}
return self_changed;
}
/*
@ -544,7 +552,7 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr, u32 error_code,
int level = PT_PAGE_TABLE_LEVEL;
int force_pt_level;
unsigned long mmu_seq;
bool map_writable;
bool map_writable, is_self_change_mapping;
pgprintk("%s: addr %lx err %x\n", __func__, addr, error_code);
@ -572,9 +580,14 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr, u32 error_code,
return 0;
}
vcpu->arch.write_fault_to_shadow_pgtable = false;
is_self_change_mapping = FNAME(is_self_change_mapping)(vcpu,
&walker, user_fault, &vcpu->arch.write_fault_to_shadow_pgtable);
if (walker.level >= PT_DIRECTORY_LEVEL)
force_pt_level = mapping_level_dirty_bitmap(vcpu, walker.gfn)
|| FNAME(is_self_change_mapping)(vcpu, &walker, user_fault);
|| is_self_change_mapping;
else
force_pt_level = 1;
if (!force_pt_level) {

22
arch/x86/kvm/x86.c
View File

@ -4751,7 +4751,8 @@ static int handle_emulation_failure(struct kvm_vcpu *vcpu)
return r;
}
static bool reexecute_instruction(struct kvm_vcpu *vcpu, gva_t cr2)
static bool reexecute_instruction(struct kvm_vcpu *vcpu, gva_t cr2,
bool write_fault_to_shadow_pgtable)
{
gpa_t gpa = cr2;
pfn_t pfn;
@ -4808,7 +4809,13 @@ static bool reexecute_instruction(struct kvm_vcpu *vcpu, gva_t cr2)
* guest to let CPU execute the instruction.
*/
kvm_mmu_unprotect_page(vcpu->kvm, gpa_to_gfn(gpa));
return true;
/*
* If the access faults on its page table, it can not
* be fixed by unprotecting shadow page and it should
* be reported to userspace.
*/
return !write_fault_to_shadow_pgtable;
}
static bool retry_instruction(struct x86_emulate_ctxt *ctxt,
@ -4867,7 +4874,13 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu,
int r;
struct x86_emulate_ctxt *ctxt = &vcpu->arch.emulate_ctxt;
bool writeback = true;
bool write_fault_to_spt = vcpu->arch.write_fault_to_shadow_pgtable;
/*
* Clear write_fault_to_shadow_pgtable here to ensure it is
* never reused.
*/
vcpu->arch.write_fault_to_shadow_pgtable = false;
kvm_clear_exception_queue(vcpu);
if (!(emulation_type & EMULTYPE_NO_DECODE)) {
@ -4886,7 +4899,8 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu,
if (r != EMULATION_OK) {
if (emulation_type & EMULTYPE_TRAP_UD)
return EMULATE_FAIL;
if (reexecute_instruction(vcpu, cr2))
if (reexecute_instruction(vcpu, cr2,
write_fault_to_spt))
return EMULATE_DONE;
if (emulation_type & EMULTYPE_SKIP)
return EMULATE_FAIL;
@ -4916,7 +4930,7 @@ restart:
return EMULATE_DONE;
if (r == EMULATION_FAILED) {
if (reexecute_instruction(vcpu, cr2))
if (reexecute_instruction(vcpu, cr2, write_fault_to_spt))
return EMULATE_DONE;
return handle_emulation_failure(vcpu);