[PATCH v5 6/5] KVM: x86: clear write_fault_to_shadow_pgtable explicitly

Xiao Guangrong
2013-01-11T14:13:09Z

On 01/11/2013 09:15 PM, Marcelo Tosatti wrote:

>
> This is cryptic. Its not obvious at all for someone modifying the code,
> for example.
>
> Can you please clear it explicitly?

Sure, this is the patch to apply your idea, is it good to you? :)

============================================
Subject: [PATCH 6/6] KVM: x86: clear write_fault_to_shadow_pgtable explicitly

Clear it explicitly when exiting x86_emulate_instruction to clarify the code,
it is suggested by Marcelo

Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
---
arch/x86/kvm/x86.c | 16 ++++++++++++----
1 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 2957012..89d01a8 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4753,7 +4753,8 @@ 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;
@@ -4816,7 +4817,7 @@ static bool reexecute_instruction(struct kvm_vcpu *vcpu, gva_t cr2)
* be fixed by unprotecting shadow page and it should
* be reported to userspace.
*/
- return !vcpu->arch.write_fault_to_shadow_pgtable;
+ return !write_fault_to_shadow_pgtable;
}

static bool retry_instruction(struct x86_emulate_ctxt *ctxt,
@@ -4875,7 +4876,13 @@ 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)) {
@@ -4894,7 +4901,8 @@ 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;
@@ -4924,7 +4932,7 @@ 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);
--
1.7.7.6