Re: [PATCH v2 2/8] x86/svm: silently drop writes to SYSCFG and related MSRs

[Jan Beulich <jbeulich@xxxxxxxx>]

On 31.08.2020 16:45, Roger Pau Monné wrote:
> On Mon, Aug 31, 2020 at 04:37:47PM +0200, Roger Pau Monné wrote:
>> On Thu, Aug 27, 2020 at 05:03:50PM +0200, Jan Beulich wrote:
>>> On 20.08.2020 17:08, Roger Pau Monne wrote:
>>>> --- a/xen/arch/x86/hvm/svm/svm.c
>>>> +++ b/xen/arch/x86/hvm/svm/svm.c
>>>> @@ -1917,6 +1917,21 @@ static int svm_msr_read_intercept(unsigned int msr, 
>>>> uint64_t *msr_content)
>>>>              goto gpf;
>>>>          break;
>>>>  
>>>> +    case MSR_K8_TOP_MEM1:
>>>> +    case MSR_K8_TOP_MEM2:
>>>> +        *msr_content = 0;
>>>> +        break;
>>>
>>> Any reason you don't fold this with ...
>>>
>>>> +    case MSR_K8_SYSCFG:
>>>> +        /*
>>>> +         * Return MtrrFixDramEn: albeit the current emulated MTRR
>>>> +         * implementation doesn't support the Extended Type-Field Format 
>>>> having
>>>> +         * such bit set is common on AMD hardware and is harmless as long 
>>>> as
>>>> +         * MtrrFixDramModEn isn't set.
>>>> +         */
>>>> +        *msr_content = K8_MTRRFIXRANGE_DRAM_ENABLE;
> 
> On the previous version you commented that returning 0 here would be
> more correct, do you still think so?

I do, but I'm still hoping to either get Andrew to agree (iirc it was
him to suggest the value above), or for me to understand why he's
wanting it this way.

Jan