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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@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>
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@ -4950,6 +4950,16 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gva_t cr2, u64 error_code,
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if (mmio_info_in_cache(vcpu, cr2, direct))
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emulation_type = 0;
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emulate:
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/*
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* On AMD platforms, under certain conditions insn_len may be zero on #NPF.
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* This can happen if a guest gets a page-fault on data access but the HW
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* table walker is not able to read the instruction page (e.g instruction
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* page is not present in memory). In those cases we simply restart the
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* guest.
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*/
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if (unlikely(insn && !insn_len))
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return 1;
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er = x86_emulate_instruction(vcpu, cr2, emulation_type, insn, insn_len);
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switch (er) {
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@ -2436,7 +2436,8 @@ static int pf_interception(struct vcpu_svm *svm)
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u64 error_code = svm->vmcb->control.exit_info_1;
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return kvm_handle_page_fault(&svm->vcpu, error_code, fault_address,
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svm->vmcb->control.insn_bytes,
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static_cpu_has(X86_FEATURE_DECODEASSISTS) ?
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svm->vmcb->control.insn_bytes : NULL,
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svm->vmcb->control.insn_len);
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}
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@ -2447,7 +2448,8 @@ static int npf_interception(struct vcpu_svm *svm)
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trace_kvm_page_fault(fault_address, error_code);
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return kvm_mmu_page_fault(&svm->vcpu, fault_address, error_code,
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svm->vmcb->control.insn_bytes,
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static_cpu_has(X86_FEATURE_DECODEASSISTS) ?
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svm->vmcb->control.insn_bytes : NULL,
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svm->vmcb->control.insn_len);
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}
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