Re: [PATCH] KVM: arm64: Fix TRFCR_EL1/PMSCR_EL1 access in hVHE mode

From: Oliver Upton <oliver.upton@linux.dev>
To: Marc Zyngier <maz@kernel.org>
Cc: kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org,
	kvm@vger.kernel.org, James Morse <james.morse@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Zenghui Yu <yuzenghui@huawei.com>,
	James Clark <james.clark@arm.com>,
	Anshuman Khandual <anshuman.khandual@arm.com>
Subject: Re: [PATCH] KVM: arm64: Fix TRFCR_EL1/PMSCR_EL1 access in hVHE mode
Date: Thu, 29 Feb 2024 17:37:08 +0000	[thread overview]
Message-ID: <ZeDAxL9nr_qmYGS9@linux.dev> (raw)
In-Reply-To: <20240229145417.3606279-1-maz@kernel.org>

Hey,

On Thu, Feb 29, 2024 at 02:54:17PM +0000, Marc Zyngier wrote:
> When running in hVHE mode, EL1 accesses are performed with the EL12
> accessor, as we run with HCR_EL2.E2H=1.
> 
> Unfortunately, both PMSCR_EL1 and TRFCR_EL1 are used with the
> EL1 accessor, meaning that we actually affect the EL2 state. Duh.
> 
> Switch to using the {read,write}_sysreg_el1() helpers that will do
> the right thing in all circumstances.

I was wondering if there was a way to surface these screw-ups at compile
time, but there's nothing elegant that comes to mind. Guess we need to
be very careful reviewing "nVHE" changes going forward.

> Note that the 'Fixes:' tag doesn't represent the point where the bug
> was introduced (there is no such point), but the first practical point
> where the hVHE feature is usable.
> 
> Cc: James Clark <james.clark@arm.com>
> Cc: Anshuman Khandual <anshuman.khandual@arm.com>
> Fixes: 38cba55008e5 ("KVM: arm64: Force HCR_E2H in guest context when ARM64_KVM_HVHE is set")
> Signed-off-by: Marc Zyngier <maz@kernel.org>

Reviewed-by: Oliver Upton <oliver.upton@linux.dev>

-- 
Thanks,
Oliver