KVM: X86: Restart the guest when insn_len is zero and SEV is enabled (00b10fe1) · Commits · 戴 / test

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>

arch/x86/kvm/mmu.c

+10 −0

Original line number	Diff line number	Diff line
		@@ -4950,6 +4950,16 @@ 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) {

arch/x86/kvm/svm.c

+4 −2

Original line number	Diff line number	Diff line
		@@ -2436,7 +2436,8 @@ 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);
		}

		@@ -2447,7 +2448,8 @@ 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);
		}

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