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>

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index e5e66e5c664057bb5cc5ad2660008ccbf19b69e5..d5e5dbd0e5ad9d2a22a5eeb9455f4108e9375e9c 100644 (file)
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -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) {

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 3e848f952b4fde6692f5ebe970dde8c17603fe49..ec5df575299525fe6ce587e42daae714248e3fd7 100644 (file)
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -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);
 }