On 02/13/2018 12:49 PM, Roman Kagan wrote:
> From: Vitaly Kuznetsov <vkuzn...@redhat.com>
>
> 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 <rkrc...@redhat.com>
> Suggested-by: Paolo Bonzini <pbonz...@redhat.com>
> Signed-off-by: Vitaly Kuznetsov <vkuzn...@redhat.com>
> Acked-by: Michael S. Tsirkin <m...@redhat.com>
> Signed-off-by: Radim Krčmář <rkrc...@redhat.com>
> [rkagan: the problem pertains to ESXi as well]
> (cherry picked from commit d391f1207067268261add0485f0f34503539c5b0)
> [rkagan: adjusted for vz7.7]
> VZ-Bug: #PSBM-81462
> Signed-off-by: Roman Kagan <rka...@virtuozzo.com>
> ---
>  arch/x86/kvm/vmx.c | 18 ++++++++++++++++--
>  arch/x86/kvm/x86.c |  3 ++-
>  2 files changed, 18 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index d94946a07de6..8ab2b3d42adc 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -5934,9 +5934,23 @@ static int handle_ept_misconfig(struct kvm_vcpu *vcpu)
>  
>       gpa = vmcs_read64(GUEST_PHYSICAL_ADDRESS);
>       if (!kvm_io_bus_write(vcpu->kvm, KVM_FAST_MMIO_BUS, gpa, 0, NULL)) {
> -             skip_emulated_instruction(vcpu);
>               trace_kvm_fast_mmio(gpa);
> -             return 1;
> +             /*
> +              * 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)) {
> +                     skip_emulated_instruction(vcpu);
> +                     return 1;
> +             } else
> +                     return x86_emulate_instruction(vcpu, gpa, EMULTYPE_SKIP,
> +                                                    NULL, 0) == EMULATE_DONE;
>       }
>  
>       ret = handle_mmio_page_fault(vcpu, gpa, true);
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index c3103bdd2d37..ddb3c2529ca8 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5503,7 +5503,8 @@ 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;
7.7 depends whether we will build new kernel or now.
Mandatory to have this in HCI branch.

Den
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