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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1783124485; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Udq3/2zgh/qo/G71V2iT9d+CQ5RvaKNE12ZPGhXw2jY=; b=w9EOB3lTthCQPBsNqGF0bkCe84OTmUAadNbqCqOqT6Tf04IVwAjVDBq6bEf04vFnKX2nT8 yMb88Y1+zhV7rAqQXWZTAykCx9MzYm33aVeoJrIrbDf+C0z2gjstdeJkxBmc4aZBleuH5n +EJ4Ga97YxepfCd5rdwfTSQGuPRqDtA= From: Ihor Solodrai To: Borislav Petkov , Dave Hansen , Ingo Molnar , Thomas Gleixner Cc: Alexei Starovoitov , Andrii Nakryiko , Andrey Ryabinin , Andrew Morton , "H . Peter Anvin" , Andrey Konovalov , bpf@vger.kernel.org, kernel-team@meta.com, kasan-dev@googlegroups.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH v1 5/5] x86/cpu: Don't reset boot CPU cpuinfo in identify_cpu() Date: Fri, 3 Jul 2026 17:20:46 -0700 Message-ID: <20260704002046.3859585-6-ihor.solodrai@linux.dev> In-Reply-To: <20260704002046.3859585-1-ihor.solodrai@linux.dev> References: <20260704002046.3859585-1-ihor.solodrai@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 X-Migadu-Flow: FLOW_OUT identify_cpu() used to rebuild c->x86_capability from scratch: init_cpu_info() memsets the capability array to zero and identify_cpu() then re-reads CPUID. On the boot CPU identify_cpu() runs after local_irq_enable() and before alternatives are patched. An interrupt delivered in the window between the memset() and get_cpu_cap() therefore will observe cleared x86_capability [1]. However the boot CPU's capabilities have already been scanned, with interrupts off, by early_identify_cpu(). So move the init_cpu_info() call out of identify_cpu() into its callers, and skip it for the boot CPU on 64-bit. Secondary CPUs call init_cpu_info() then identify_cpu() from identify_secondary_cpu(), with interrupts off, exactly as before. 32-bit still resets in identify_boot_cpu(): it relies on the reset for the no-CPUID cpuid_level default. [1] https://lore.kernel.org/bpf/20260610175651.647515-1-ihor.solodrai@linux.dev/ Signed-off-by: Ihor Solodrai --- arch/x86/kernel/cpu/common.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 8f093c6c7ccc..cd3d7c37c174 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -1986,8 +1986,6 @@ static void identify_cpu(struct cpuinfo_x86 *c) c->loops_per_jiffy = loops_per_jiffy; - init_cpu_info(c); - if (!cpuid_feature()) identify_cpu_without_cpuid(c); @@ -2156,6 +2154,13 @@ static void identify_cpu_32(struct cpuinfo_x86 *c) static __init void identify_boot_cpu(void) { + /* + * The boot CPU's capabilities were already scanned in early_identify_cpu(). + * However 32-bit still needs to init_cpu_info() here for the no-CPUID + * cpuid_level default. + */ + if (IS_ENABLED(CONFIG_X86_32)) + init_cpu_info(&boot_cpu_data); identify_cpu(&boot_cpu_data); if (HAS_KERNEL_IBT && cpu_feature_enabled(X86_FEATURE_IBT)) pr_info("CET detected: Indirect Branch Tracking enabled\n"); @@ -2178,6 +2183,7 @@ void identify_secondary_cpu(unsigned int cpu) *c = boot_cpu_data; c->cpu_index = cpu; + init_cpu_info(c); identify_cpu(c); identify_cpu_32(c); x86_spec_ctrl_setup_ap(); -- 2.54.0