From: Marc Zyngier <maz@kernel.org>
To: linux-arm-kernel@lists.infradead.org,
kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org
Cc: Andrew Murray <andrew.murray@arm.com>,
James Morse <james.morse@arm.com>,
Julien Thierry Julien Thierry <julien.thierry.kdev@gmail.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>
Subject: [PATCH] KVM: arm64: pmu: Fix cycle counter truncation on counter stop
Date: Thu, 3 Oct 2019 18:24:00 +0100 [thread overview]
Message-ID: <20191003172400.21157-1-maz@kernel.org> (raw)
When a counter is disabled, its value is sampled before the event
is being disabled, and the value written back in the shadow register.
In that process, the value gets truncated to 32bit, which is adequate
for any counter but the cycle counter, which can be configured to
hold a 64bit value. This obviously results in a corrupted counter,
and things like "perf record -e cycles" not working at all when
run in a guest...
Make the truncation conditional on the counter not being 64bit.
Fixes: 80f393a23be6 ("KVM: arm/arm64: Support chained PMU counters")
Cc: Andrew Murray <andrew.murray@arm.com>
Reported-by: Julien Thierry Julien Thierry <julien.thierry.kdev@gmail.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
virt/kvm/arm/pmu.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/virt/kvm/arm/pmu.c b/virt/kvm/arm/pmu.c
index 362a01886bab..d716aef2bae9 100644
--- a/virt/kvm/arm/pmu.c
+++ b/virt/kvm/arm/pmu.c
@@ -206,9 +206,11 @@ static void kvm_pmu_stop_counter(struct kvm_vcpu *vcpu, struct kvm_pmc *pmc)
__vcpu_sys_reg(vcpu, reg) = lower_32_bits(counter);
__vcpu_sys_reg(vcpu, reg + 1) = upper_32_bits(counter);
} else {
+ if (!kvm_pmu_idx_is_64bit(vcpu, pmc->idx))
+ counter = lower_32_bits(counter);
reg = (pmc->idx == ARMV8_PMU_CYCLE_IDX)
? PMCCNTR_EL0 : PMEVCNTR0_EL0 + pmc->idx;
- __vcpu_sys_reg(vcpu, reg) = lower_32_bits(counter);
+ __vcpu_sys_reg(vcpu, reg) = counter;
}
kvm_pmu_release_perf_event(pmc);
--
2.20.1
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next reply other threads:[~2019-10-03 17:24 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-03 17:24 Marc Zyngier [this message]
2019-10-04 8:55 ` [PATCH] KVM: arm64: pmu: Fix cycle counter truncation on counter stop Andrew Murray
2019-10-04 10:08 ` Marc Zyngier
2019-10-04 14:10 ` Andrew Murray
2019-10-04 14:42 ` Marc Zyngier
2019-10-04 15:06 ` Andrew Murray
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20191003172400.21157-1-maz@kernel.org \
--to=maz@kernel.org \
--cc=andrew.murray@arm.com \
--cc=james.morse@arm.com \
--cc=julien.thierry.kdev@gmail.com \
--cc=kvm@vger.kernel.org \
--cc=kvmarm@lists.cs.columbia.edu \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=suzuki.poulose@arm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).