From: Marc Zyngier <maz@kernel.org>
To: Karl Mehltretter <kmehltretter@gmail.com>
Cc: Oliver Upton <oupton@kernel.org>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Andre Przywara <andre.przywara@arm.com>,
linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] KVM: arm64: Preserve GPRs for AArch32 CP64 reads generating an UNDEF
Date: Mon, 10 Aug 2026 09:41:00 +0100 [thread overview]
Message-ID: <86se4m9xlv.wl-maz@kernel.org> (raw)
In-Reply-To: <20260802182222.2239-1-kmehltretter@gmail.com>
On Sun, 02 Aug 2026 19:22:22 +0100,
Karl Mehltretter <kmehltretter@gmail.com> wrote:
>
> kvm_handle_cp_64() only seeds params.regval for writes. If a CP64 read is
> decoded but UNDEFs, emulate_cp() still returns handled and the caller
> writes params.regval back to Rt/Rt2.
>
> This can happen for PMU counter read accesses generating an UNDEF. KVM
> injects the exception into the guest, so the MRRC GPRs must remain
> unchanged.
>
> Instead, the uninitialised regval is copied into the guest GPRs. With stack
> auto-initialisation this is a deterministic zero or pattern value. With
> CONFIG_INIT_STACK_NONE it may be stale host stack data.
>
> Match kvm_handle_cp_32() and kvm_handle_sys_reg() by seeding regval from
> the GPRs before emulation.
>
> Fixes: 62a89c44954f0 ("arm64: KVM: 32bit handling of coprocessor traps")
> Assisted-by: Claude:claude-opus-5
> Signed-off-by: Karl Mehltretter <kmehltretter@gmail.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
M.
--
Without deviation from the norm, progress is not possible.
prev parent reply other threads:[~2026-08-10 8:41 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-08-02 18:22 [PATCH v2] KVM: arm64: Preserve GPRs for AArch32 CP64 reads generating an UNDEF Karl Mehltretter
2026-08-03 6:32 ` Marc Zyngier
2026-08-10 8:41 ` Marc Zyngier [this message]
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