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KVM: X86: Restart the guest when insn_len is zero and SEV is enabled

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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>
This commit is contained in:
Brijesh Singh 2017-12-04 10:57:40 -06:00
parent 35c6f649bb
commit 00b10fe104
2 changed files with 14 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
arch/x86/kvm/mmu.c
View File

@ -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) {

6
arch/x86/kvm/svm.c
View File

@ -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);
}