From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta1.migadu.com (out-85.mta1.migadu.com [95.215.58.85]) (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 9D48538944E for ; Tue, 25 Aug 2026 16:42:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.85 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787676158; cv=none; b=Te405B13vhItl2gyYOV0rvJI3ThYu8i1Zre0+w4zif5N2U2zbWKiJTO/2s+mvYY5pqMkedMBLmGJSahGZxY+IiRpgnEpaAs2umDkFLpQPI4+NG58tMxZ6XyaLBRdvIelBdHVF1l0k75saueo0zjL29twjabzoA+tiAAF4SMCD48= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787676158; c=relaxed/simple; bh=CYocrFWmtpehijgOQcGCt0ml+hOpQBMXbSBN0pxWBYg=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=jfSJf7/Or+WEFWWo7dHAqCdt+g979oRd4xO4Ld2z7b4NBe/+QFItt/P5A0/Rvuvwqg1KkfIMwBHXhKO/jIrJSEVJygFwQgGsU6SozC+Mp14JRtwv/VTmxYF+47NATqv7FyV+AGo8luSbz55ghoZZ+1PLNBF4yzfVXBJgyRveL44= 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=h/3l8OqF; arc=none smtp.client-ip=95.215.58.85 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="h/3l8OqF" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=CYocrFWmtpehijgOQcGCt0ml+hOpQBMXbSBN0pxWBYg=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1787676154; v=1; x=1788280954; b=h/3l8OqFwZfY77u+/ur1hFq103jfMJ9kpESQwXqjQ/0w8oPXX1QGLKDk5FTdyLD9TqCe5bAI tLIiTIoov8PXdykCWf1yz36O4hJC0rCr+nWfx5nL4JqM0iwr4KKpnvYgHp48JDcHguREISdYIvb Yme+R6F35RrEtxLi2xfmi52o= X-Envelope-To: linux-kernel@vger.kernel.org Received: from claudy.local (2a01:4b00:ad36:1d00:3a05:25ff:fe33:35a9) by smtp.migadu.com with ESMTPS id 5c13a4e79d66ea44; Tue, 25 Aug 2026 16:42:34 +0000 X-Mizu-Trace-ID: 5c13a4e79d66ea44 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 v4 2/2] arm64: Don't read GMID_EL1 when MTE is disabled Date: Tue, 25 Aug 2026 17:42:19 +0100 Message-Id: <20260825164219.3347229-3-fuad.tabba@linux.dev> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20260825164219.3347229-1-fuad.tabba@linux.dev> References: <20260825164219.3347229-1-fuad.tabba@linux.dev> 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 __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 --- arch/arm64/include/asm/cpufeature.h | 9 +++++++++ arch/arm64/kernel/cpufeature.c | 6 ++---- arch/arm64/kernel/cpuinfo.c | 2 +- 3 files changed, 12 insertions(+), 5 deletions(-) diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h index a57870fa96db5..0b374e938f708 100644 --- a/arch/arm64/include/asm/cpufeature.h +++ b/arch/arm64/include/asm/cpufeature.h @@ -1085,6 +1085,15 @@ static inline bool cpu_has_lpa2(void) #endif } +/* No ID register reflects CONFIG_ARM64_MTE. */ +static inline bool gmid_el1_accessible(void) +{ + if (!IS_ENABLED(CONFIG_ARM64_MTE)) + return false; + + return id_aa64pfr1_mte(__read_sysreg_by_encoding(SYS_ID_AA64PFR1_EL1)); +} + #endif /* __ASSEMBLER__ */ #endif diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c index 88b15b5ef2f7f..23f174b3c4e26 100644 --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -1228,7 +1228,7 @@ 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()) init_cpu_ftr_reg(SYS_GMID_EL1, info->reg_gmid); } @@ -1523,11 +1523,9 @@ 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()) 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..389fca84f106b 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->reg_gmid = read_cpuid(GMID_EL1); if (id_aa64pfr0_32bit_el0(info->reg_id_aa64pfr0)) -- 2.39.5