Re: [PATCH v1 0/2] KVM: arm64: PMU: Correct the handling of PMUSERENR_EL0

From: Marc Zyngier <maz@kernel.org>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Reiji Watanabe <reijiw@google.com>,
	Oliver Upton <oliver.upton@linux.dev>,
	kvmarm@lists.linux.dev, kvm@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	James Morse <james.morse@arm.com>,
	Alexandru Elisei <alexandru.elisei@arm.com>,
	Zenghui Yu <yuzenghui@huawei.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Ricardo Koller <ricarkol@google.com>,
	Jing Zhang <jingzhangos@google.com>,
	Raghavendra Rao Anata <rananta@google.com>,
	Will Deacon <will@kernel.org>
Subject: Re: [PATCH v1 0/2] KVM: arm64: PMU: Correct the handling of PMUSERENR_EL0
Date: Tue, 04 Apr 2023 11:05:11 +0100	[thread overview]
Message-ID: <86ttxwufmw.wl-maz@kernel.org> (raw)
In-Reply-To: <20230329002136.2463442-1-reijiw@google.com>

+ Mark, as we just discussed this.

On Wed, 29 Mar 2023 01:21:34 +0100,
Reiji Watanabe <reijiw@google.com> wrote:
> 
> This series will fix bugs in KVM's handling of PMUSERENR_EL0.
> 
> With PMU access support from EL0 [1], the perf subsystem would
> set CR and ER bits of PMUSERENR_EL0 as needed to allow EL0 to have
> a direct access to PMU counters.  However, KVM appears to assume
> that the register value is always zero for the host EL0, and has
> the following two problems in handling the register.
> 
> [A] The host EL0 might lose the direct access to PMU counters, as
>     KVM always clears PMUSERENR_EL0 before returning to userspace.
> 
> [B] With VHE, the guest EL0 access to PMU counters might be trapped
>     to EL1 instead of to EL2 (even when PMUSERENR_EL0 for the guest
>     indicates that the guest EL0 has an access to the counters).
>     This is because, with VHE, KVM sets ER, CR, SW and EN bits of
>     PMUSERENR_EL0 to 1 on vcpu_load() to ensure to trap PMU access
>     from the guset EL0 to EL2, but those bits might be cleared by
>     the perf subsystem after vcpu_load() (when PMU counters are
>     programmed for the vPMU emulation).
> 
> Patch-1 will fix [A], and Patch-2 will fix [B] respectively.
> The series is based on v6.3-rc4.
> 
> [1] https://github.com/torvalds/linux/commit/83a7a4d643d33a8b74a42229346b7ed7139fcef9
> 
> Reiji Watanabe (2):
>   KVM: arm64: PMU: Restore the host's PMUSERENR_EL0
>   KVM: arm64: PMU: Ensure to trap PMU access from EL0 to EL2
> 
>  arch/arm64/include/asm/kvm_host.h       |  3 +++
>  arch/arm64/kvm/hyp/include/hyp/switch.h | 28 +++++++++++++------------
>  2 files changed, 18 insertions(+), 13 deletions(-)
> 
> 
> base-commit: 197b6b60ae7bc51dd0814953c562833143b292aa
> -- 
> 2.40.0.348.gf938b09366-goog
> 
> 

-- 
Without deviation from the norm, progress is not possible.

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