Re: [PATCH v3 4/8] x86/svm: handle BU_CFG and BU_CFG2 with cases

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 01/09/2020 11:54, Roger Pau Monne wrote:
> @@ -1942,19 +1966,6 @@ static int svm_msr_read_intercept(unsigned int msr, 
> uint64_t *msr_content)
>      default:
>          if ( rdmsr_safe(msr, *msr_content) == 0 )
>              break;
> -
> -        if ( boot_cpu_data.x86 == 0xf && msr == MSR_F10_BU_CFG )
> -        {
> -            /* Win2k8 x64 reads this MSR on revF chips, where it
> -             * wasn't publically available; it uses a magic constant
> -             * in %rdi as a password, which we don't have in
> -             * rdmsr_safe().  Since we'll ignore the later writes,
> -             * just use a plausible value here (the reset value from
> -             * rev10h chips) if the real CPU didn't provide one. */
> -            *msr_content = 0x0000000010200020ull;
> -            break;
> -        }
> -
>          goto gpf;
>      }
>  
> @@ -2110,6 +2121,12 @@ static int svm_msr_write_intercept(unsigned int msr, 
> uint64_t msr_content)
>          nsvm->ns_msr_hsavepa = msr_content;
>          break;
>  
> +    case MSR_F10_BU_CFG:
> +    case MSR_F10_BU_CFG2:
> +        if ( rdmsr_safe(msr, msr_content) )
> +            goto gpf;

The comment you've moved depends on this not having this behaviour, as
you'll now hand #GP back to Win2k8 on its write.

Honestly, given that how obsolete both Win2k8 and K10's are, I'm
seriously tempted to suggest dropping this workaround entirely.

~Andrew

> +        break;
> +
>      case MSR_AMD64_TSC_RATIO:
>          if ( msr_content & TSC_RATIO_RSVD_BITS )
>              goto gpf;