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Re: [PATCH v2 2/2] x86/cpuid: Detect null segment behaviour on Zen2 CPUs
- To: Jan Beulich <jbeulich@xxxxxxxx>, Jane Malalane <jane.malalane@xxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Wed, 8 Sep 2021 13:28:35 +0100
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- Cc: Wei Liu <wl@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Pu Wen <puwen@xxxxxxxx>, Andy Lutomirski <luto@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Wed, 08 Sep 2021 12:28:50 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 08/09/2021 13:08, Jan Beulich wrote:
> On 08.09.2021 10:19, Jane Malalane wrote:
>> Zen2 CPUs actually have this behaviour, but the CPUID bit couldn't be
>> introduced into Zen2 due to a lack of leaves. So, it was added in a
>> new leaf in Zen3. Nonetheless, hypervisors can synthesize the CPUID
>> bit in software.
> Considering the prior model checks, I understand this isn't all Zen2s?
> No matter what the answer, I'd like to ask that the first sentence
> start with either "All" or "Some" (or something along these lines).
> Which is of course fine to insert while committing, so not need to
> send a v3.
All Zen2's have this behaviour.
The model checks were trying to avoid running the probe on Zen1, but
"model >= 0x30 && mode != 0x50" is error prone.
There are no faults in the probe, and its fast, so running on all Zen1/2
is better than hoping that we got the model list correct.
~Andrew
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