From: Brijesh Singh brijesh.singh@amd.com
[ Upstream commit 00b10fe1046c4b2232097a7ffaa9238c7e479388 ]
On AMD platforms, under certain conditions insn_len may be zero on #NPF. This can happen if a guest gets a page-fault on data access but the HW table walker is not able to read the instruction page (e.g instruction page is not present in memory).
Typically, when insn_len is zero, x86_emulate_instruction() walks the guest page table and fetches the instruction bytes from guest memory. When SEV is enabled, the guest memory is encrypted with guest-specific key hence hypervisor will not able to fetch the instruction bytes. In those cases we simply restart the guest.
I have encountered this issue when running kernbench inside the guest.
Cc: Thomas Gleixner tglx@linutronix.de Cc: Ingo Molnar mingo@redhat.com Cc: "H. Peter Anvin" hpa@zytor.com Cc: Paolo Bonzini pbonzini@redhat.com Cc: "Radim Krčmář" rkrcmar@redhat.com Cc: Joerg Roedel joro@8bytes.org Cc: Borislav Petkov bp@suse.de Cc: Tom Lendacky thomas.lendacky@amd.com Cc: x86@kernel.org Cc: kvm@vger.kernel.org Cc: linux-kernel@vger.kernel.org Signed-off-by: Brijesh Singh brijesh.singh@amd.com Signed-off-by: Sasha Levin alexander.levin@microsoft.com --- arch/x86/kvm/mmu.c | 10 ++++++++++ arch/x86/kvm/svm.c | 6 ++++-- 2 files changed, 14 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index cc83bdcb65d1..d9773e38b537 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -4951,6 +4951,16 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gva_t cr2, u64 error_code, if (mmio_info_in_cache(vcpu, cr2, direct)) emulation_type = 0; emulate: + /* + * On AMD platforms, under certain conditions insn_len may be zero on #NPF. + * This can happen if a guest gets a page-fault on data access but the HW + * table walker is not able to read the instruction page (e.g instruction + * page is not present in memory). In those cases we simply restart the + * guest. + */ + if (unlikely(insn && !insn_len)) + return 1; + er = x86_emulate_instruction(vcpu, cr2, emulation_type, insn, insn_len);
switch (er) { diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c index 4e3c79530526..1dbcb889e24f 100644 --- a/arch/x86/kvm/svm.c +++ b/arch/x86/kvm/svm.c @@ -2177,7 +2177,8 @@ static int pf_interception(struct vcpu_svm *svm) u64 error_code = svm->vmcb->control.exit_info_1;
return kvm_handle_page_fault(&svm->vcpu, error_code, fault_address, - svm->vmcb->control.insn_bytes, + static_cpu_has(X86_FEATURE_DECODEASSISTS) ? + svm->vmcb->control.insn_bytes : NULL, svm->vmcb->control.insn_len); }
@@ -2188,7 +2189,8 @@ static int npf_interception(struct vcpu_svm *svm)
trace_kvm_page_fault(fault_address, error_code); return kvm_mmu_page_fault(&svm->vcpu, fault_address, error_code, - svm->vmcb->control.insn_bytes, + static_cpu_has(X86_FEATURE_DECODEASSISTS) ? + svm->vmcb->control.insn_bytes : NULL, svm->vmcb->control.insn_len); }