Re: [PATCH 4.9] x86/kvm/vmx: do not use vm-exit instruction length for fast MMIO when running nested

[Greg KH <gregkh@linuxfoundation.org>]

On Sun, Jan 06, 2019 at 01:57:24PM -0500, Mike Haboustak wrote:
> [ Backport of upstream commit d391f1207067268261add0485f0f34503539c5b0 ]
> 
> 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>
> Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
> [mhaboustak: backport to 4.9.y]
> Signed-off-by: Mike Haboustak <haboustak@gmail.com>
> ---
>  arch/x86/kvm/vmx.c | 19 +++++++++++++++++--
>  arch/x86/kvm/x86.c |  3 ++-
>  2 files changed, 19 insertions(+), 3 deletions(-)

Now queued up, thanks.

greg k-h