Re: [Xen-devel] [PATCH v2] x86/vmx: correctly gather gs_shadow value for current vCPU

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

On 5/2/19 2:52 AM, Tamas K Lengyel wrote:
> Currently the gs_shadow value is only cached when the vCPU is being scheduled
> out by Xen. Reporting this (usually) stale value through vm_event is 
> incorrect,
> since it doesn't represent the actual state of the vCPU at the time the event
> was recorded. This prevents vm_event subscribers from correctly finding kernel
> structures in the guest when it is trapped while in ring3.
> 
> Refresh shadow_gs value when the context being saved is for the current vCPU.
> 
> Signed-off-by: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>
> Cc: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
> Cc: Jun Nakajima <jun.nakajima@xxxxxxxxx>
> Cc: Kevin Tian <kevin.tian@xxxxxxxxx>
> Cc: Jan Beulich <jbeulich@xxxxxxxx>
> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Cc: Wei Liu <wei.liu2@xxxxxxxxxx>
> Cc: Roger Pau Monne <roger.pau@xxxxxxxxxx>
> ---
> v2: move fix to hvm so vm_event doesn't have to know specifics
> ---
>  xen/arch/x86/hvm/vmx/vmx.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
> index 283eb7b34d..5154ecc2a8 100644
> --- a/xen/arch/x86/hvm/vmx/vmx.c
> +++ b/xen/arch/x86/hvm/vmx/vmx.c
> @@ -779,12 +779,17 @@ static void vmx_load_cpu_state(struct vcpu *v, struct 
> hvm_hw_cpu *data)
>  
>  static void vmx_save_vmcs_ctxt(struct vcpu *v, struct hvm_hw_cpu *ctxt)
>  {
> +    if ( v == current )
> +        vmx_save_guest_msrs(v);

vmx_save_guest_msrs() is simple enough that the if is probably not
necessary here (we can just call the function directly, regardless of
what v holds).

But that's not technically an issue, so if nobody else minds:

Acked-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>


Thanks,
Razvan

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