This is a note to let you know that I've just added the patch titled

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

to the 4.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: kvm-x86-restart-the-guest-when-insn_len-is-zero-and-sev-is-enabled.patch and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From foo@baz Fri Mar 16 15:11:07 CET 2018

From: Brijesh Singh brijesh.singh@amd.com Date: Mon, 4 Dec 2017 10:57:40 -0600 Subject: KVM: X86: Restart the guest when insn_len is zero and SEV is enabled

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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kvm/mmu.c | 10 ++++++++++ arch/x86/kvm/svm.c | 6 ++++-- 2 files changed, 14 insertions(+), 2 deletions(-)

--- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -4951,6 +4951,16 @@ int kvm_mmu_page_fault(struct kvm_vcpu * 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) { --- a/arch/x86/kvm/svm.c +++ b/arch/x86/kvm/svm.c @@ -2178,7 +2178,8 @@ static int pf_interception(struct vcpu_s 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); }

@@ -2189,7 +2190,8 @@ static int npf_interception(struct vcpu_

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); }

Patches currently in stable-queue which might be from brijesh.singh@amd.com are

queue-4.15/kvm-x86-restart-the-guest-when-insn_len-is-zero-and-sev-is-enabled.patch