Re: [RFC PATCH v6 75/92] kvm: x86: disable gpa_available optimization in emulator_read_write_onepage()
From: Paolo Bonzini <pbonzini@redhat.com>
Date: 2019-08-13 08:47:40
Also in:
kvm, linux-mm
Subsystem:
kernel virtual machine for x86 (kvm/x86), the rest, x86 architecture (32-bit and 64-bit) · Maintainers:
Sean Christopherson, Paolo Bonzini, Linus Torvalds, Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen
On 09/08/19 18:00, Adalbert Lazăr wrote:
If the EPT violation was caused by an execute restriction imposed by the introspection tool, gpa_available will point to the instruction pointer, not the to the read/write location that has to be used to emulate the current instruction. This optimization should be disabled only when the VM is introspected, not just because the introspection subsystem is present. Signed-off-by: Adalbert Lazăr <redacted>
The right thing to do is to not set gpa_available for fetch failures in kvm_mmu_page_fault instead:
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 24843cf49579..1bdca40fa831 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c@@ -5364,8 +5364,12 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gva_t cr2, u64 error_code, enum emulation_result er; bool direct = vcpu->arch.mmu->direct_map; - /* With shadow page tables, fault_address contains a GVA or nGPA. */ - if (vcpu->arch.mmu->direct_map) { + /* + * With shadow page tables, fault_address contains a GVA or nGPA. + * On a fetch fault, fault_address contains the instruction pointer. + */ + if (vcpu->arch.mmu->direct_map && + likely(!(error_code & PFERR_FETCH_MASK)) { vcpu->arch.gpa_available = true; vcpu->arch.gpa_val = cr2; }
Paolo
quoted hunk ↗ jump to hunk
--- arch/x86/kvm/x86.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 965c4f0108eb..3975331230b9 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c@@ -5532,7 +5532,7 @@ static int emulator_read_write_onepage(unsigned long addr, void *val, * operation using rep will only have the initial GPA from the NPF * occurred. */ - if (vcpu->arch.gpa_available && + if (vcpu->arch.gpa_available && !kvmi_is_present() && emulator_can_use_gpa(ctxt) && (addr & ~PAGE_MASK) == (vcpu->arch.gpa_val & ~PAGE_MASK)) { gpa = vcpu->arch.gpa_val;
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