From: Catalin Marinas <catalin.marinas@arm.com>
To: Fuad Tabba <fuad.tabba@linux.dev>
Cc: Will Deacon <will@kernel.org>,
linux-arm-kernel@lists.infradead.org,
Marc Zyngier <maz@kernel.org>, Oliver Upton <oupton@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Mark Brown <broonie@kernel.org>,
kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org,
Fuad Tabba <tabba@google.com>
Subject: Re: [PATCH v4 2/2] arm64: Don't read GMID_EL1 when MTE is disabled
Date: Wed, 26 Aug 2026 14:48:01 +0100 [thread overview]
Message-ID: <ao7ukb2xewCp92uc@arm.com> (raw)
In-Reply-To: <20260825164219.3347229-3-fuad.tabba@linux.dev>
On Tue, Aug 25, 2026 at 05:42:19PM +0100, Fuad Tabba wrote:
> __cpuinfo_store_cpu() gates the GMID_EL1 read on the raw
> ID_AA64PFR1_EL1, so it reads the register even when the kernel has
> disabled MTE (CONFIG_ARM64_MTE=n or arm64.nomte). KVM sets HCR_EL2.TID5
> in that case, and pKVM injects an UNDEF the host cannot handle:
>
> Internal error: Oops - Undefined instruction: 0000000002000000 [#1] SMP
> pc : __cpuinfo_store_cpu+0xf4/0x264
> Kernel panic - not syncing: Attempted to kill the idle task!
>
> Only pKVM reaches it, and only after a CPU is offlined and brought back
> online: its CPU_ON relay sets the host HCR before the CPU enters EL1,
> while plain nVHE sets it at CPUHP_AP_KVM_ONLINE.
>
> Gate the read on __read_sysreg_by_encoding(), which applies the cmdline
> override, and on CONFIG_ARM64_MTE, which no register reflects.
>
> Fixes: f35abcbb8a084 ("KVM: arm64: Trap MTE access and discovery when MTE is disabled")
> Cc: stable@vger.kernel.org # needs "arm64: Apply overrides to CPU local capabilities"
> Signed-off-by: Fuad Tabba <fuad.tabba@linux.dev>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
next prev parent reply other threads:[~2026-08-26 13:48 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-08-25 16:42 [PATCH v4 0/2] arm64: Clamp ID overrides and gate the GMID_EL1 read Fuad Tabba
2026-08-25 16:42 ` [PATCH v4 1/2] arm64: Apply overrides to CPU local capabilities Fuad Tabba
2026-08-26 13:47 ` Catalin Marinas
2026-08-27 8:58 ` Fuad Tabba
2026-08-25 16:42 ` [PATCH v4 2/2] arm64: Don't read GMID_EL1 when MTE is disabled Fuad Tabba
2026-08-26 13:48 ` Catalin Marinas [this message]
2026-08-27 12:56 ` Will Deacon
2026-08-27 13:19 ` Will Deacon
2026-08-28 10:50 ` Catalin Marinas
2026-08-28 13:53 ` Will Deacon
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