linux-kernel - Re: [Xen-devel] [RFC PATCH 02/16] x86/xen: cpuid support in xenhost

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Message-ID: <2f5188ae-e542-57b5-ed12-83dd3cbbafbd@citrix.com>
Date:   Wed, 12 Jun 2019 22:09:20 +0100
From:   Andrew Cooper <andrew.cooper3@...rix.com>
To:     Ankur Arora <ankur.a.arora@...cle.com>,
        <linux-kernel@...r.kernel.org>, <xen-devel@...ts.xenproject.org>
CC:     <jgross@...e.com>, <sstabellini@...nel.org>,
        <konrad.wilk@...cle.com>, <pbonzini@...hat.com>,
        <boris.ostrovsky@...cle.com>, <joao.m.martins@...cle.com>
Subject: Re: [Xen-devel] [RFC PATCH 02/16] x86/xen: cpuid support in xenhost_t

On 09/05/2019 18:25, Ankur Arora wrote:
> xen_cpuid_base() is used to probe and setup features early in a
> guest's lifetime.
>
> We want this to behave differently depending on xenhost->type: for
> instance, local xenhosts cannot intercept the cpuid instruction at all.
>
> Add op (*cpuid_base)() in xenhost_ops_t.
>
> Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>

What is the real layout of hypervisor nesting here?

When Xen is at L0, all HVM guests get working CPUID faulting to combat
this problem, because CPUID faulting can be fully emulated even on older
Intel hardware, and AMD hardware.

It is a far cleaner way of fixing the problem.

~Andrew