On 1/03/2024 11:52 am, Sean Christopherson wrote:
On Fri, Mar 01, 2024, Kai Huang wrote:
On 28/02/2024 3:41 pm, Sean Christopherson wrote:
Move the sanity check that hardware never sets bits that collide with KVM-
define synthetic bits from kvm_mmu_page_fault() to npf_interception(),
i.e. make the sanity check #NPF specific. The legacy #PF path already
WARNs if _any_ of bits 63:32 are set, and the error code that comes from
VMX's EPT Violatation and Misconfig is 100% synthesized (KVM morphs VMX's
EXIT_QUALIFICATION into error code flags).
Add a compile-time assert in the legacy #PF handler to make sure that KVM-
define flags are covered by its existing sanity check on the upper bits.
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
arch/x86/kvm/mmu/mmu.c | 12 +++---------
arch/x86/kvm/svm/svm.c | 9 +++++++++
2 files changed, 12 insertions(+), 9 deletions(-)
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 5d892bd59c97..bd342ebd0809 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4561,6 +4561,9 @@ int kvm_handle_page_fault(struct kvm_vcpu *vcpu, u64 error_code,
if (WARN_ON_ONCE(error_code >> 32))
error_code = lower_32_bits(error_code);
+ /* Ensure the above sanity check also covers KVM-defined flags. */
+ BUILD_BUG_ON(lower_32_bits(PFERR_SYNTHETIC_MASK));
+
Could you explain why adding this BUILD_BUG_ON() here, but not ...
vcpu->arch.l1tf_flush_l1d = true;
if (!flags) {
trace_kvm_page_fault(vcpu, fault_address, error_code);
@@ -5845,15 +5848,6 @@ int noinline kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 err
int r, emulation_type = EMULTYPE_PF;
bool direct = vcpu->arch.mmu->root_role.direct;
- /*
- * WARN if hardware generates a fault with an error code that collides
- * with KVM-defined sythentic flags. Clear the flags and continue on,
- * i.e. don't terminate the VM, as KVM can't possibly be relying on a
- * flag that KVM doesn't know about.
- */
- if (WARN_ON_ONCE(error_code & PFERR_SYNTHETIC_MASK))
- error_code &= ~PFERR_SYNTHETIC_MASK;
-
if (WARN_ON_ONCE(!VALID_PAGE(vcpu->arch.mmu->root.hpa)))
return RET_PF_RETRY;
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index e90b429c84f1..199c4dd8d214 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -2055,6 +2055,15 @@ static int npf_interception(struct kvm_vcpu *vcpu)
u64 fault_address = svm->vmcb->control.exit_info_2;
u64 error_code = svm->vmcb->control.exit_info_1;
+ /*
+ * WARN if hardware generates a fault with an error code that collides
+ * with KVM-defined sythentic flags. Clear the flags and continue on,
+ * i.e. don't terminate the VM, as KVM can't possibly be relying on a
+ * flag that KVM doesn't know about.
+ */
+ if (WARN_ON_ONCE(error_code & PFERR_SYNTHETIC_MASK))
+ error_code &= ~PFERR_SYNTHETIC_MASK;
+
trace_kvm_page_fault(vcpu, fault_address, error_code);
return kvm_mmu_page_fault(vcpu, fault_address, error_code,
static_cpu_has(X86_FEATURE_DECODEASSISTS) ?
... in npf_interception() or
The intent of the BUILD_BUG_ON() is to ensure that kvm_handle_page_fault()'s
sanity check that bits 63:32 also serves as a sanity check that hardware doesn't
generate an error code that collides with any of KVM's synthetic flags.
E.g. if we were to add a KVM-defined flag in the lower 32 bits, then the #NPF
path would Just Work, because it already sanity checks all synthetic bits. But
the #PF path would need new code, thus the BUILD_BUG_ON() to scream that new code
is needed.
Ah, right. Thanks for explaining :-)
Reviewed-by: Kai Huang <kai.huang@xxxxxxxxx>
