Re: [PATCH 3/8] x86/pv: handle writes to the EFER MSR

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 17/08/2020 16:57, Roger Pau Monne wrote:
> @@ -1005,6 +1013,13 @@ static int write_msr(unsigned int reg, uint64_t val,
>          curr->arch.pv.gs_base_user = val;
>          return X86EMUL_OKAY;
>  
> +    case MSR_EFER:
> +        /* Silently drop writes that don't change the reported value. */
> +        temp = guest_efer(currd);
> +        if ( val != temp )
> +            goto invalid;

break.

The invalid label does write-discard, rather than injecting #GP.

The comment would be clearer as "Reject writes which change the value,
but tolerate no-op writes", seeing as that is the compatibility
behaviour we're adding.

~Andrew