From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta0.migadu.com (out-88.mta0.migadu.com [91.218.175.88]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B72CC3914F0 for ; Thu, 27 Aug 2026 18:59:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.88 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787857193; cv=none; b=pIkXaBSc/japc3D3ymD7V/r7jpnhmeydRZ8Ny8b3ot8CTiypdOaZH+/ln1INpAcgoSdqwnjfgKl8id6QdkjbxtNPQAeZF0BbF2JaT9YBCikK489Za2NL+eKuUIQH8GvxzBnyQhNJuIjz424xrfbDxNludh+/8mxRFmwc3NmA6EY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787857193; c=relaxed/simple; bh=uKyFPMySg+ZdcSjFgmGmteIutliy7r49MnJ4aFTwets=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=PixC/w6M7BDkpnWBBAsNRgUlp2Ngr9KXmuAIqCiolhH5HbvvRj/bMpXzcIZ46rU7AyTJf0uUYhv8bTC+CHK3z0c7qfk8zzA1tw5NPal+wRHPhlOGBbUhps9Q8RjpkQcGVYLLp5kJFqlaxYjmg+mTYrE+qjOnYvxEZcGt2VKhLis= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=lL7+11+0; arc=none smtp.client-ip=91.218.175.88 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="lL7+11+0" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=uKyFPMySg+ZdcSjFgmGmteIutliy7r49MnJ4aFTwets=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1787857187; v=1; x=1788461987; b=lL7+11+0a2Un64Yzv2/4QoUirmZXacYdwmh2Qa6RY4dzevcdWx4NGxQwbk13rZB3oIWjqN/4 +Vy8T+4FHqYXiuFZIuFDg3EEs3Ww3e1C2+FzVdK4OJ8HD9QHEkJXvlumgPk2xpfCA8XD+3lxToh F6msYL5mX6A727KiS14Ll/3o= X-Envelope-To: linux-kernel@vger.kernel.org Received: by smtp.migadu.com with ESMTPS id f547417c01070e20; Thu, 27 Aug 2026 18:59:37 +0000 X-Mizu-Trace-ID: f547417c01070e20 X-Migadu-Flow: FLOW_OUT From: Fuad Tabba To: Catalin Marinas , Will Deacon , linux-arm-kernel@lists.infradead.org Cc: Marc Zyngier , Oliver Upton , Mark Rutland , Suzuki K Poulose , Mark Brown , kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, Fuad Tabba Subject: [PATCH v5] arm64: Don't read GMID_EL1 when MTE is disabled Date: Thu, 27 Aug 2026 19:59:37 +0100 Message-Id: <20260827185937.1369099-1-fuad.tabba@linux.dev> X-Mailer: git-send-email 2.39.5 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit __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 the CPU's own ID_AA64PFR1_EL1 with the command-line override applied, and on CONFIG_ARM64_MTE, which no register reflects. The boot CPU stores its registers before init_cpu_features() strips an unsafe override, so clamp against the hardware value here too. Fixes: f35abcbb8a084 ("KVM: arm64: Trap MTE access and discovery when MTE is disabled") Cc: stable@vger.kernel.org Signed-off-by: Fuad Tabba --- Notes: Changes since v4: - Gate on the ID_AA64PFR1_EL1 that __cpuinfo_store_cpu() has already read, clamping the override against it in cpufeature.c, rather than adding a __read_sysreg_by_encoding() caller in the header (Will). The register is not read a second time. - Dropped Suzuki's override clamp, which this no longer needs. It is worth having on its own, so I'll post it separately with the Fixes: tag and without the update_cpu_ftr_reg() hunk (Catalin). Tested on QEMU under pKVM, with -machine virt,mte=on. Offline/online CPU1 with arm64.nomte: unpatched panics in __cpuinfo_store_cpu(), patched does not. Same with CONFIG_ARM64_MTE=n and no override on the command line. And with id_aa64pfr1.mte=2 on a CPU without FEAT_MTE2, where the clamp keeps the gate false and init_cpu_ftr_reg() drops the override afterwards. arch/arm64/include/asm/cpu.h | 1 + arch/arm64/include/asm/cpufeature.h | 7 ------ arch/arm64/kernel/cpufeature.c | 33 +++++++++++++++++++++++++---- arch/arm64/kernel/cpuinfo.c | 2 +- 4 files changed, 31 insertions(+), 12 deletions(-) diff --git a/arch/arm64/include/asm/cpu.h b/arch/arm64/include/asm/cpu.h index 71493b760b839..3c008821219c2 100644 --- a/arch/arm64/include/asm/cpu.h +++ b/arch/arm64/include/asm/cpu.h @@ -78,5 +78,6 @@ void __init cpuinfo_store_boot_cpu(void); void __init init_cpu_features(struct cpuinfo_arm64 *info); void update_cpu_features(int cpu, struct cpuinfo_arm64 *info, struct cpuinfo_arm64 *boot); +bool gmid_el1_accessible(const struct cpuinfo_arm64 *info); #endif /* __ASM_CPU_H */ diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h index a57870fa96db5..f6a7200700ccf 100644 --- a/arch/arm64/include/asm/cpufeature.h +++ b/arch/arm64/include/asm/cpufeature.h @@ -627,13 +627,6 @@ static inline bool id_aa64pfr1_mpamfrac(u64 pfr1) return val > 0; } -static inline bool id_aa64pfr1_mte(u64 pfr1) -{ - u32 val = cpuid_feature_extract_unsigned_field(pfr1, ID_AA64PFR1_EL1_MTE_SHIFT); - - return val >= ID_AA64PFR1_EL1_MTE_MTE2; -} - void __init setup_boot_cpu_features(void); void __init setup_system_features(void); void __init setup_user_features(void); diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c index 9a22df0c5120f..103e70d683ca2 100644 --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -1176,6 +1176,33 @@ static bool detect_ftr_has_mpam(void) return id_aa64pfr0_mpam(pfr0) || id_aa64pfr1_mpamfrac(pfr1); } +bool gmid_el1_accessible(const struct cpuinfo_arm64 *info) +{ + const struct arm64_ftr_bits *ftrp; + s64 mte, ovr; + u64 ftr_mask; + + /* No ID register reflects CONFIG_ARM64_MTE. */ + if (!IS_ENABLED(CONFIG_ARM64_MTE)) + return false; + + for (ftrp = ftr_id_aa64pfr1; ftrp->width; ftrp++) { + if (ftrp->shift == ID_AA64PFR1_EL1_MTE_SHIFT) + break; + } + + ftr_mask = arm64_ftr_mask(ftrp); + mte = arm64_ftr_value(ftrp, info->reg_id_aa64pfr1); + + /* The boot CPU runs before init_cpu_ftr_reg() strips unsafe overrides. */ + if ((id_aa64pfr1_override.mask & ftr_mask) == ftr_mask) { + ovr = arm64_ftr_value(ftrp, id_aa64pfr1_override.val); + mte = arm64_ftr_safe_value(ftrp, ovr, mte); + } + + return mte >= ID_AA64PFR1_EL1_MTE_MTE2; +} + void __init init_cpu_features(struct cpuinfo_arm64 *info) { /* Before we start using the tables, make sure it is sorted */ @@ -1228,7 +1255,7 @@ void __init init_cpu_features(struct cpuinfo_arm64 *info) init_cpu_ftr_reg(SYS_MPAMIDR_EL1, info->reg_mpamidr); } - if (id_aa64pfr1_mte(info->reg_id_aa64pfr1)) + if (gmid_el1_accessible(info)) init_cpu_ftr_reg(SYS_GMID_EL1, info->reg_gmid); } @@ -1490,11 +1517,9 @@ void update_cpu_features(int cpu, * they read/write depends on the GMID_EL1.BS field. Check that the * value is the same on all CPUs. */ - if (IS_ENABLED(CONFIG_ARM64_MTE) && - id_aa64pfr1_mte(info->reg_id_aa64pfr1)) { + if (gmid_el1_accessible(info)) taint |= check_update_ftr_reg(SYS_GMID_EL1, cpu, info->reg_gmid, boot->reg_gmid); - } /* * If we don't have AArch32 at all then skip the checks entirely diff --git a/arch/arm64/kernel/cpuinfo.c b/arch/arm64/kernel/cpuinfo.c index d50e2a9b066b3..45c63f3d75c53 100644 --- a/arch/arm64/kernel/cpuinfo.c +++ b/arch/arm64/kernel/cpuinfo.c @@ -502,7 +502,7 @@ static void __cpuinfo_store_cpu(struct cpuinfo_arm64 *info) info->reg_id_aa64smfr0 = read_cpuid(ID_AA64SMFR0_EL1); info->reg_id_aa64fpfr0 = read_cpuid(ID_AA64FPFR0_EL1); - if (id_aa64pfr1_mte(info->reg_id_aa64pfr1)) + if (gmid_el1_accessible(info)) info->reg_gmid = read_cpuid(GMID_EL1); if (id_aa64pfr0_32bit_el0(info->reg_id_aa64pfr0)) -- 2.39.5