Re: [Qemu-devel] [PATCH] WHPX fixes an issue with CPUID 1 not returning CPUID_EXT_HYPERVISOR

[Eduardo Habkost <ehabkost@redhat.com>]

On Mon, Mar 26, 2018 at 10:06:58AM -0700, Justin Terry (VM) wrote:
> Implements the CPUID trap for CPUID 1 to include the
> CPUID_EXT_HYPERVISOR flag in the ECX results. This was preventing some
> older linux kernels from booting when trying to access MSR's that dont
> make sense when virtualized.
> 
> Signed-off-by: Justin Terry (VM) <juterry@microsoft.com>
> ---
>  target/i386/whpx-all.c | 79 +++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 78 insertions(+), 1 deletion(-)
> 
> diff --git a/target/i386/whpx-all.c b/target/i386/whpx-all.c
> index bf33d320bf..58435178a4 100644
> --- a/target/i386/whpx-all.c
> +++ b/target/i386/whpx-all.c
> @@ -911,12 +911,62 @@ static int whpx_vcpu_run(CPUState *cpu)
>              ret = 1;
>              break;
>  
> +        case WHvRunVpExitReasonX64Cpuid: {
> +            WHV_REGISTER_VALUE reg_values[5] = {0};
> +            WHV_REGISTER_NAME reg_names[5];
> +            UINT32 reg_count = 5;
> +            UINT64 rip, rax, rcx, rdx, rbx;
> +
> +            rip = vcpu->exit_ctx.VpContext.Rip +
> +                  vcpu->exit_ctx.VpContext.InstructionLength;
> +            switch (vcpu->exit_ctx.CpuidAccess.Rax) {
> +            case 1:
> +                rax = vcpu->exit_ctx.CpuidAccess.DefaultResultRax;
> +                /* Advertise that we are running on a hypervisor */
> +                rcx =
> +                    vcpu->exit_ctx.CpuidAccess.DefaultResultRcx |
> +                    CPUID_EXT_HYPERVISOR;
> +
> +                rdx = vcpu->exit_ctx.CpuidAccess.DefaultResultRdx;
> +                rbx = vcpu->exit_ctx.CpuidAccess.DefaultResultRbx;
> +                break;
> +            default:
> +                rax = vcpu->exit_ctx.CpuidAccess.DefaultResultRax;
> +                rcx = vcpu->exit_ctx.CpuidAccess.DefaultResultRcx;
> +                rdx = vcpu->exit_ctx.CpuidAccess.DefaultResultRdx;
> +                rbx = vcpu->exit_ctx.CpuidAccess.DefaultResultRbx;

Interesting, so the WHPX API already tries to provide default
values for the CPUID leaves.  Would it make sense to try and use
the values returned by cpu_x86_cpuid() in the future?

Is there a way to get the default CPUID results from the WHPX API
without calling WHvRunVirtualProcessor(), so QEMU can be aware of
what exactly the guest is seeing on CPUID?


> +            }
> +
> +            reg_names[0] = WHvX64RegisterRip;
> +            reg_names[1] = WHvX64RegisterRax;
> +            reg_names[2] = WHvX64RegisterRcx;
> +            reg_names[3] = WHvX64RegisterRdx;
> +            reg_names[4] = WHvX64RegisterRbx;
> +
> +            reg_values[0].Reg64 = rip;
> +            reg_values[1].Reg64 = rax;
> +            reg_values[2].Reg64 = rcx;
> +            reg_values[3].Reg64 = rdx;
> +            reg_values[4].Reg64 = rbx;
> +
> +            hr = WHvSetVirtualProcessorRegisters(whpx->partition,
> +                                                 cpu->cpu_index,
> +                                                 reg_names,
> +                                                 reg_count,
> +                                                 reg_values);
> +
> +            if (FAILED(hr)) {
> +                error_report("WHPX: Failed to set CpuidAccess state registers,"
> +                             " hr=%08lx", hr);
> +            }
> +            ret = 0;
> +            break;
> +        }
>          case WHvRunVpExitReasonNone:
>          case WHvRunVpExitReasonUnrecoverableException:
>          case WHvRunVpExitReasonInvalidVpRegisterValue:
>          case WHvRunVpExitReasonUnsupportedFeature:
>          case WHvRunVpExitReasonX64MsrAccess:
> -        case WHvRunVpExitReasonX64Cpuid:
>          case WHvRunVpExitReasonException:
>          default:
>              error_report("WHPX: Unexpected VP exit code %d",
> @@ -1272,6 +1322,33 @@ static int whpx_accel_init(MachineState *ms)
>          goto error;
>      }
>  
> +    memset(&prop, 0, sizeof(WHV_PARTITION_PROPERTY));
> +    prop.ExtendedVmExits.X64CpuidExit = 1;
> +    hr = WHvSetPartitionProperty(whpx->partition,
> +                                 WHvPartitionPropertyCodeExtendedVmExits,
> +                                 &prop,
> +                                 sizeof(WHV_PARTITION_PROPERTY));
> +
> +    if (FAILED(hr)) {
> +        error_report("WHPX: Failed to enable partition extended X64CpuidExit"
> +                     " hr=%08lx", hr);
> +        ret = -EINVAL;
> +        goto error;
> +    }
> +
> +    UINT32 cpuidExitList[] = {1};
> +    hr = WHvSetPartitionProperty(whpx->partition,
> +                                 WHvPartitionPropertyCodeCpuidExitList,
> +                                 cpuidExitList,
> +                                 RTL_NUMBER_OF(cpuidExitList) * sizeof(UINT32));
> +
> +    if (FAILED(hr)) {
> +        error_report("WHPX: Failed to set partition CpuidExitList hr=%08lx",
> +                     hr);
> +        ret = -EINVAL;
> +        goto error;
> +    }
> +
>      hr = WHvSetupPartition(whpx->partition);
>      if (FAILED(hr)) {
>          error_report("WHPX: Failed to setup partition, hr=%08lx", hr);
> -- 
> 2.11.0
> 

-- 
Eduardo