diff options
| author | Vitaly Kuznetsov <vkuznets@redhat.com> | 2018-01-25 16:37:07 +0100 |
|---|---|---|
| committer | Radim Krčmář <rkrcmar@redhat.com> | 2018-01-31 18:25:34 +0100 |
| commit | d391f1207067268261add0485f0f34503539c5b0 (patch) | |
| tree | b6fbb28c52ff362013c2ca10763369febb2db1e9 | |
| parent | kvm: embed vcpu id to dentry of vcpu anon inode (diff) | |
| download | linux-d391f1207067268261add0485f0f34503539c5b0.tar.xz linux-d391f1207067268261add0485f0f34503539c5b0.zip | |
x86/kvm/vmx: do not use vm-exit instruction length for fast MMIO when running nested
I was investigating an issue with seabios >= 1.10 which stopped working
for nested KVM on Hyper-V. The problem appears to be in
handle_ept_violation() function: when we do fast mmio we need to skip
the instruction so we do kvm_skip_emulated_instruction(). This, however,
depends on VM_EXIT_INSTRUCTION_LEN field being set correctly in VMCS.
However, this is not the case.
Intel's manual doesn't mandate VM_EXIT_INSTRUCTION_LEN to be set when
EPT MISCONFIG occurs. While on real hardware it was observed to be set,
some hypervisors follow the spec and don't set it; we end up advancing
IP with some random value.
I checked with Microsoft and they confirmed they don't fill
VM_EXIT_INSTRUCTION_LEN on EPT MISCONFIG.
Fix the issue by doing instruction skip through emulator when running
nested.
Fixes: 68c3b4d1676d870f0453c31d5a52e7e65c7448ae
Suggested-by: Radim Krčmář <rkrcmar@redhat.com>
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
| -rw-r--r-- | arch/x86/kvm/vmx.c | 16 | ||||
| -rw-r--r-- | arch/x86/kvm/x86.c | 3 |
2 files changed, 17 insertions, 2 deletions
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index 1e2ca9e8662f..438802d0b01d 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -6577,7 +6577,21 @@ static int handle_ept_misconfig(struct kvm_vcpu *vcpu) if (!is_guest_mode(vcpu) && !kvm_io_bus_write(vcpu, KVM_FAST_MMIO_BUS, gpa, 0, NULL)) { trace_kvm_fast_mmio(gpa); - return kvm_skip_emulated_instruction(vcpu); + /* + * Doing kvm_skip_emulated_instruction() depends on undefined + * behavior: Intel's manual doesn't mandate + * VM_EXIT_INSTRUCTION_LEN to be set in VMCS when EPT MISCONFIG + * occurs and while on real hardware it was observed to be set, + * other hypervisors (namely Hyper-V) don't set it, we end up + * advancing IP with some random value. Disable fast mmio when + * running nested and keep it for real hardware in hope that + * VM_EXIT_INSTRUCTION_LEN will always be set correctly. + */ + if (!static_cpu_has(X86_FEATURE_HYPERVISOR)) + return kvm_skip_emulated_instruction(vcpu); + else + return x86_emulate_instruction(vcpu, gpa, EMULTYPE_SKIP, + NULL, 0) == EMULATE_DONE; } ret = kvm_mmu_page_fault(vcpu, gpa, PFERR_RSVD_MASK, NULL, 0); diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 0204b2b8a293..01571102b50c 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -5773,7 +5773,8 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, * handle watchpoints yet, those would be handled in * the emulate_ops. */ - if (kvm_vcpu_check_breakpoint(vcpu, &r)) + if (!(emulation_type & EMULTYPE_SKIP) && + kvm_vcpu_check_breakpoint(vcpu, &r)) return r; ctxt->interruptibility = 0; |