From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E0B36244686; Tue, 29 Apr 2025 17:40:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745948456; cv=none; b=LfTuT3wifO6Ad9TBPPE92eZBD4d/72a0BVaDL4febpSrJNIcYSGKn+wNrjYI9IIpDzb9uKGoNoXz059ZBUm/DFlxawd9e79YlXd2vOxqA+CPrpfAs2UxdSORU4eEOrdpvvZCVGyD/2NOZ9CJ8tgv2rLydAfxKjH5k2kOpppctQ8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745948456; c=relaxed/simple; bh=cHJ7dwYQ7n23rgXBlMOzmLnoczSe1Q7ISQAaHC2jCCI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=sn8fm0HDxRqunmA7FXl3kFD3b/ib2Wi5J1gELu5PZ6y+ht79xVfwbbj7nSr99/GnCrWoj2NeG3cue/kr+2j2zlob8YZniu7H5q2/YxJrASN4E+VFos8Jm/Z4Nn2uKM+kxS7F0Fgzm9HhFswXx984HxGS7M1OERjhhlxo7OhHg0s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=J2J9hjcv; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="J2J9hjcv" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 73649C4CEE3; Tue, 29 Apr 2025 17:40:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1745948455; bh=cHJ7dwYQ7n23rgXBlMOzmLnoczSe1Q7ISQAaHC2jCCI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=J2J9hjcvpUFBzmvMxW7EkSiUfZMM/qvlqoO4SIWeeA+so4MCN1KfzHo9IA0T04zut 05H2M2dXbTXIZV0bhUIen3jC4RcNks5KmUkderrcbG3wxfcqGxdnOZOoTPtjy/X/tw Nfiai9XAmLUQHjJz7uuCX33PTeOtB9NUhK/q3HjI= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Max Grobecker , Ingo Molnar , linux-kernel@vger.kernel.org, Borislav Petkov , Sasha Levin Subject: [PATCH 5.15 013/373] x86/cpu: Dont clear X86_FEATURE_LAHF_LM flag in init_amd_k8() on AMD when running in a virtual machine Date: Tue, 29 Apr 2025 18:38:10 +0200 Message-ID: <20250429161123.680833280@linuxfoundation.org> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250429161123.119104857@linuxfoundation.org> References: <20250429161123.119104857@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 5.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Max Grobecker [ Upstream commit a4248ee16f411ac1ea7dfab228a6659b111e3d65 ] When running in a virtual machine, we might see the original hardware CPU vendor string (i.e. "AuthenticAMD"), but a model and family ID set by the hypervisor. In case we run on AMD hardware and the hypervisor sets a model ID < 0x14, the LAHF cpu feature is eliminated from the the list of CPU capabilities present to circumvent a bug with some BIOSes in conjunction with AMD K8 processors. Parsing the flags list from /proc/cpuinfo seems to be happening mostly in bash scripts and prebuilt Docker containers, as it does not need to have additionals tools present – even though more reliable ways like using "kcpuid", which calls the CPUID instruction instead of parsing a list, should be preferred. Scripts, that use /proc/cpuinfo to determine if the current CPU is "compliant" with defined microarchitecture levels like x86-64-v2 will falsely claim the CPU is incapable of modern CPU instructions when "lahf_lm" is missing in that flags list. This can prevent some docker containers from starting or build scripts to create unoptimized binaries. Admittably, this is more a small inconvenience than a severe bug in the kernel and the shoddy scripts that rely on parsing /proc/cpuinfo should be fixed instead. This patch adds an additional check to see if we're running inside a virtual machine (X86_FEATURE_HYPERVISOR is present), which, to my understanding, can't be present on a real K8 processor as it was introduced only with the later/other Athlon64 models. Example output with the "lahf_lm" flag missing in the flags list (should be shown between "hypervisor" and "abm"): $ cat /proc/cpuinfo processor : 0 vendor_id : AuthenticAMD cpu family : 15 model : 6 model name : Common KVM processor stepping : 1 microcode : 0x1000065 cpu MHz : 2599.998 cache size : 512 KB physical id : 0 siblings : 1 core id : 0 cpu cores : 1 apicid : 0 initial apicid : 0 fpu : yes fpu_exception : yes cpuid level : 13 wp : yes flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 syscall nx rdtscp lm rep_good nopl cpuid extd_apicid tsc_known_freq pni pclmulqdq ssse3 fma cx16 sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c hypervisor abm 3dnowprefetch vmmcall bmi1 avx2 bmi2 xsaveopt ... while kcpuid shows the feature to be present in the CPU: # kcpuid -d | grep lahf lahf_lm - LAHF/SAHF available in 64-bit mode [ mingo: Updated the comment a bit, incorporated Boris's review feedback. ] Signed-off-by: Max Grobecker Signed-off-by: Ingo Molnar Cc: linux-kernel@vger.kernel.org Cc: Borislav Petkov Signed-off-by: Sasha Levin --- arch/x86/kernel/cpu/amd.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c index ce5b27db65e10..a8dc7fe5f1003 100644 --- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -811,7 +811,7 @@ static void init_amd_k8(struct cpuinfo_x86 *c) * (model = 0x14) and later actually support it. * (AMD Erratum #110, docId: 25759). */ - if (c->x86_model < 0x14 && cpu_has(c, X86_FEATURE_LAHF_LM)) { + if (c->x86_model < 0x14 && cpu_has(c, X86_FEATURE_LAHF_LM) && !cpu_has(c, X86_FEATURE_HYPERVISOR)) { clear_cpu_cap(c, X86_FEATURE_LAHF_LM); if (!rdmsrl_amd_safe(0xc001100d, &value)) { value &= ~BIT_64(32); -- 2.39.5