Re: [Xen-devel] [PATCH v4 11/26] xen/x86: Improvements to in-hypervisor cpuid sanity checks

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 24/03/16 16:47, Jan Beulich wrote:
>>>> On 23.03.16 at 17:36, <andrew.cooper3@xxxxxxxxxx> wrote:
>> +        if ( !is_pvh_domain(currd) )
>>          {
>> -            __clear_bit(X86_FEATURE_XSAVE % 32, &c);
>> -            __clear_bit(X86_FEATURE_AVX % 32, &c);
>> +            /*
>> +             * Delete the PVH condition when HVMLite formally replaces PVH,
>> +             * and HVM guests no longer enter a PV codepath.
>> +             */
>> +
>> +            /* OSXSAVE cleared by pv_featureset.  Fast-forward CR4 back in. 
>> */
>> +            if ( (is_pv_domain(currd) && guest_kernel_mode(curr, regs) &&
>> +                  (read_cr4() & X86_CR4_OSXSAVE)) ||
>> +                 (curr->arch.pv_vcpu.ctrlreg[4] & X86_CR4_OSXSAVE) )
>> +                c |= cpufeat_mask(X86_FEATURE_OSXSAVE);
>>          }
> The is_pv_domain() is now redundant with the is_pvh_domain()
> earlier on, and it would likely end up confusing the reader if on
> the right side of the || then ->arch.pv_vcpu is being referenced.

I specifically chose to order the code like this to make it easier to
remove the is_pvh_domain() conditional in the future, without having to
re-edit the PV path.

This layout matches the OSPKE version, and I would prefer to keep it
this way unless you really insist on changing it.

~Andrew

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