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Re: [PATCH 3/3] x86: Use CpuidUserDis if an AMD HVM guest toggles CPUID faulting
- To: Jan Beulich <jbeulich@xxxxxxxx>, Alejandro Vallejo <alejandro.vallejo@xxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Tue, 9 May 2023 11:05:33 +0100
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 09 May 2023 10:06:01 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 08/05/2023 2:18 pm, Jan Beulich wrote:
> On 05.05.2023 19:57, Alejandro Vallejo wrote:
>> This is in order to aid guests of AMD hardware that we have exposed
>> CPUID faulting to. If they try to modify the Intel MSR that enables
>> the feature, trigger levelling so AMD's version of it (CpuidUserDis)
>> is used instead.
>>
>> Signed-off-by: Alejandro Vallejo <alejandro.vallejo@xxxxxxxxx>
>> ---
>> xen/arch/x86/msr.c | 9 ++++++++-
>> 1 file changed, 8 insertions(+), 1 deletion(-)
> Don't you also need to update cpu-policy.c:calculate_host_policy()
> for the guest to actually know it can use the functionality? Which
> in turn would appear to require some form of adjustment to
> lib/x86/policy.c:x86_cpu_policies_are_compatible().
I asked Alejandro to do it like this.
Advertising this to guests requires plumbing another MSR into the
infrastructure which isn't quite set up properly let, and is in flux
from my work.
For now, this just lets Xen enforce the policy over PV guests, which is
an improvement in and of itself.
~Andrew
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