Re: [PATCH] KVM: x86: remove PMU FIXED_CTR3 from msrs_to_save_all

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On 1/18/22 06:04, Wang, Wei W wrote:
On Tuesday, January 18, 2022 11:54 AM, Jim Mattson wrote:
On Fri, Dec 17, 2021 at 6:05 AM Wei Wang <wei.w.wang@xxxxxxxxx> wrote:

The fixed counter 3 is used for the Topdown metrics, which hasn't been
enabled for KVM guests. Userspace accessing to it will fail as it's
not included in get_fixed_pmc(). This breaks KVM selftests on ICX+
machines, which have this counter.

To reproduce it on ICX+ machines, ./state_test reports:
==== Test Assertion Failure ====
lib/x86_64/processor.c:1078: r == nmsrs
pid=4564 tid=4564 - Argument list too long
1  0x000000000040b1b9: vcpu_save_state at processor.c:1077
2  0x0000000000402478: main at state_test.c:209 (discriminator 6)
3  0x00007fbe21ed5f92: ?? ??:0
4  0x000000000040264d: _start at ??:?
  Unexpected result from KVM_GET_MSRS, r: 17 (failed MSR was 0x30c)

With this patch, it works well.

Signed-off-by: Wei Wang <wei.w.wang@xxxxxxxxx>
Reviewed-and-tested-by: Jim Mattson <jmattson@xxxxxxxxxx>

I believe this fixes commit 2e8cd7a3b828 ("kvm: x86: limit the maximum
number of vPMU fixed counters to 3") from v5.9. Should this be cc'ed to
stable?

Sounds good to me.

Sent, thanks.

Paolo




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