Reword the BUILD_BUG_ON() comment in the legacy #PF handler to explicitly describe how asserting that synthetic PFERR flags are limited to bits 31:0 protects KVM against inadvertently passing a synthetic flag to the common page fault handler. No functional change intended. Suggested-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx> --- arch/x86/kvm/mmu/mmu.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 8d7115230739..2421d971ce1b 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -4599,7 +4599,10 @@ 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. */ + /* + * Restrict KVM-defined flags to bits 63:32 so that it's impossible for + * them to conflict with #PF error codes, which are limited to 32 bits. + */ BUILD_BUG_ON(lower_32_bits(PFERR_SYNTHETIC_MASK)); vcpu->arch.l1tf_flush_l1d = true; base-commit: b9adc10edd4e14e66db4f7289a88fdbfa45ae7a8 -- 2.45.2.505.gda0bf45e8d-goog
