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Re: [PATCH for-4.20] x86/intel: Fix PERF_GLOBAL fixup when virtualised
- To: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Mon, 27 Jan 2025 12:42:29 +0000
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- Cc: Jonathan Katz <jonathan.katz@xxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Mon, 27 Jan 2025 12:42:40 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 21/01/2025 4:57 pm, Oleksii Kurochko wrote:
>
> On 1/21/25 3:25 PM, Andrew Cooper wrote:
>> Logic using performance counters needs to look at
>> MSR_MISC_ENABLE.PERF_AVAILABLE before touching any other resources.
>>
>> When virtualised under ESX, Xen dies with a #GP fault trying to read
>> MSR_CORE_PERF_GLOBAL_CTRL.
>>
>> Factor this logic out into a separate function (it's already too
>> squashed to
>> the RHS), and insert a check of MSR_MISC_ENABLE.PERF_AVAILABLE.
>>
>> This also limits setting X86_FEATURE_ARCH_PERFMON, although oprofile
>> (the only
>> consumer of this flag) cross-checks too.
>>
>> Reported-by: Jonathan Katz <jonathan.katz@xxxxxxxxx>
>> Link: https://xcp-ng.org/forum/topic/10286/nesting-xcp-ng-on-esx-8
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>> ---
>> CC: Jan Beulich <JBeulich@xxxxxxxx>
>> CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>> CC: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
>>
>> Untested, but this is the same pattern used by oprofile and watchdog
>> setup.
>
> Probably it will make sense to wait for a response on the forum (you
> mentioned in the Link:) that the current one patch works?
It's been a week. At this point it needs to go in for the release. As
I said, this is exactly the same pattern as used elsewhere in Xen, so
I'm confident it's a good fix, and Roger agrees too.
~Andrew
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