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. Thanks, Roger.
