[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH for-4.16] x86/cpuid: prevent shrinking migrated policies max leaves
On 11/11/2021 14:04, Roger Pau Monné wrote: > On Thu, Nov 11, 2021 at 10:26:29AM +0100, Jan Beulich wrote: >> On 10.11.2021 19:17, Andrew Cooper wrote: >>> On 10/11/2021 17:40, Roger Pau Monne wrote: >>>> diff --git a/tools/libs/guest/xg_cpuid_x86.c >>>> b/tools/libs/guest/xg_cpuid_x86.c >>>> index 198892ebdf..3ffd5f683b 100644 >>>> --- a/tools/libs/guest/xg_cpuid_x86.c >>>> +++ b/tools/libs/guest/xg_cpuid_x86.c >>>> @@ -638,6 +638,13 @@ int xc_cpuid_apply_policy(xc_interface *xch, uint32_t >>>> domid, bool restore, >>>> } >>>> } >>>> >>>> + /* >>>> + * Do not try to shrink the policy if restoring, as that could cause >>>> + * guest visible changes in the maximum leaf fields. >>>> + */ >>>> + if ( !restore ) >>>> + x86_cpuid_policy_shrink_max_leaves(p); >>> Nothing in xc_cpuid_apply_policy() changes any of the max leaves, so >>> this is dead logic. >> I guess you mean nothing there does anything which would result in >> shrinking of the max leaves by calling this function? Yet even if >> so, isn't the call here to take care of any earlier changes which >> might have resulted in fully blank tail leaves? > AFAICT the featureset (optionally) passed in as a parameter could > result in certain leaves being zeroed and thus allow for the max leaf > to shrink. > > So while xc_cpuid_apply_policy doesn't change the max leaves fields, > it can potentially zero certain leaves allowing to shrink the reported > max leaf. Hmm true, although I don't anticipate this having an effect in practice. Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
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