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Date: Wed, 1 Nov 2017 16:17:23 -0500 From: Brijesh Singh <brijesh.singh@....com> To: kvm@...r.kernel.org, linux-kernel@...r.kernel.org Cc: bp@...en8.de, Brijesh Singh <brijesh.singh@....com>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, Paolo Bonzini <pbonzini@...hat.com>, Radim Krčmář <rkrcmar@...hat.com>, Joerg Roedel <joro@...tes.org>, Borislav Petkov <bp@...e.de>, Tom Lendacky <thomas.lendacky@....com>, x86@...nel.org Subject: [Part2 PATCH v7 38/38] KVM: X86: Restart the guest when insn_len is zero and SEV is enabled 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@...utronix.de> Cc: Ingo Molnar <mingo@...hat.com> Cc: "H. Peter Anvin" <hpa@...or.com> Cc: Paolo Bonzini <pbonzini@...hat.com> Cc: "Radim Krčmář" <rkrcmar@...hat.com> Cc: Joerg Roedel <joro@...tes.org> Cc: Borislav Petkov <bp@...e.de> Cc: Tom Lendacky <thomas.lendacky@....com> Cc: x86@...nel.org Cc: kvm@...r.kernel.org Cc: linux-kernel@...r.kernel.org Signed-off-by: Brijesh Singh <brijesh.singh@....com> --- arch/x86/kvm/mmu.c | 10 ++++++++++ arch/x86/kvm/svm.c | 3 ++- 2 files changed, 12 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index 7a69cf053711..0d4776b855bb 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -4954,6 +4954,16 @@ 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 29c30ecde780..3299d0d2ee1d 100644 --- a/arch/x86/kvm/svm.c +++ b/arch/x86/kvm/svm.c @@ -2410,7 +2410,8 @@ 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, !npt_enabled); } -- 2.9.5
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