Re: [Xen-devel] [PATCH] x86/HVM: hide features dependent on XSAVE when booted with "no-xsave"

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 27/11/15 11:07, Jan Beulich wrote:
> ... or when the guest has the XSAVE feature hidden by CPUID policy.
> Not doing so is at best confusing to guests.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> One question is whether we shouldn't switch leaf 7 to white listing,
> just like done for PV guests.

The general comments from my PV side review apply here as well.

My levelling series has also moved all cpuid information to
whitelist-based.  It is the only safe way of doing things.

I chose to defer AVX512 work from my levelling series, because it is
rather more complicated than this, and there was insufficient details in
the Extention reference.  In particular, there is an suggestion that one
of the feature bits indicates support for non-EVEX encoded instructions
with k$N opmasks, which is not dependent on AVX512F.

It is also odd to see it added to HVM guests but not PV.  I would be
tempted to leave all the AVX512 bits until the groundwork from my series
is in.  It is destined for Skylake-EP which is still a year off.

~Andrew

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