From: Dongli Si <kvmx86@gmail.com>
To: peterz@infradead.org
Cc: acme@kernel.org, alexander.shishkin@linux.intel.com,
bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com,
jolsa@kernel.org, joro@8bytes.org, kim.phillips@amd.com,
kvmx86@gmail.com, liam.merwick@oracle.com,
linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org,
mark.rutland@arm.com, mingo@kernel.org, namhyung@kernel.org,
tglx@linutronix.de, x86@kernel.org
Subject: Re: [PATCH v4] perf/x86/amd: Don't touch the Host-only bit inside the guest hypervisor
Date: Mon, 11 Apr 2022 21:40:53 +0800 [thread overview]
Message-ID: <20220411134053.738799-1-sidongli1997@gmail.com> (raw)
In-Reply-To: <Ykb400opkmZFsnVN@hirez.programming.kicks-ass.net>
On Fri, 1 Apr 2022 15:06:27 +0200, Peter Zijlstra wrote:
> If SVM enter/exit don't twiddle with counter EN bits, how is all this
> supposed to work consistently then?
Since KVM currently does not support the "Host/Guest Only" bits (41:40),
CPU wide events created on L1 HV will always count L1 HV and L2, so no
twiddle counter EN bits are needed when {dis,en}abling SVM on L1 HV.
This #GP warning is because KVM does not allow guest to set HO/GO bit,
It has been fixed in this commit 9b026073db2f
("KVM: x86/svm: Clear reserved bits written to PerfEvtSeln MSRs")
and has been merged to 5.18-rc1.
Because the commit df51fe7ea1c1c
("perf/x86/amd: Don't touch the AMD64_EVENTSEL_HOSTONLY bit inside the guest")
is to fix a very similar problem caused by the same reason,
I think it should be revert now, it make things obscure.
And perf_ctr_virt_mask is used to mask Host-Only bit when SVM is disabled,
Using it on a guest doesn't make sense and make things obscure.
I wrote a patch to clarifies what perf_ctr_virt_mask does.
Regards,
Dongli
prev parent reply other threads:[~2022-04-11 13:41 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-20 0:21 [PATCH v4] perf/x86/amd: Don't touch the Host-only bit inside the guest hypervisor Dongli Si
2022-03-24 10:42 ` Peter Zijlstra
2022-03-27 10:56 ` Dongli Si
2022-03-28 14:03 ` Peter Zijlstra
2022-04-01 8:29 ` Dongli Si
2022-04-01 13:06 ` Peter Zijlstra
2022-04-11 13:40 ` Dongli Si [this message]
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