From nobody Sat Feb 7 14:19:33 2026 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 2CFA0143736; Wed, 23 Apr 2025 14:55:42 +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=1745420142; cv=none; b=T3npLzqxz4LjA3GQwh6SBzz3MzbfADArhBLPq3YB8XUzcZXswVQEGmtJU094daYuFx0RZogVwMFubWwBrV6253v/sSjTS+5M00Mb0BPS/M0Iw5aCOb4x2Q4TDUJmMKRZPD89727zmWhX3r9qF4w2fk+qmN5gejOTAuYJNXxSW4E= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745420142; c=relaxed/simple; bh=oDo3UZgN2f0i5SU10aU0wh8oxr5T89ZFV8R4Orckq3g=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=O9UFEKDrd1Xly85tRsKUhbqoqfhPVdNDELBsgTOstpA50sA2bnL8GqaPltmLw/xQwK0OFINhQWOjJOy7+FfAgt0w1Aqal+uvC7u0kl2NuBSSmOJY8DNjkRE5sxF+h+PJ3QmU/tGJunmLczTzpc+nMe+C8jAIv8EKqI3WV454OT8= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=tEKOF5AJ; 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="tEKOF5AJ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9FE3FC4CEE2; Wed, 23 Apr 2025 14:55:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1745420142; bh=oDo3UZgN2f0i5SU10aU0wh8oxr5T89ZFV8R4Orckq3g=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=tEKOF5AJdI6dvv1qWrqGB9O8/fu8TuTK7z8o0nvkbT3IgYq+BIvI0JlJdfopstZZX tOlSn3IOykmT3EolEmSTqHL1BxxlwnlS95sE8uMPqHT4K6kio1mqijC7Yzu4/Ui6rm aeHuTkp8eqRrJUJe8oOwOqCm2KI3JT34bqbpFFkc= 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 6.6 042/393] x86/cpu: Dont clear X86_FEATURE_LAHF_LM flag in init_amd_k8() on AMD when running in a virtual machine Date: Wed, 23 Apr 2025 16:38:58 +0200 Message-ID: <20250423142645.029766418@linuxfoundation.org> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250423142643.246005366@linuxfoundation.org> References: <20250423142643.246005366@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable 6.6-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 wi= th 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 =E2=80=93 even though more reliable ways like usi= ng "kcpuid", which calls the CPUID instruction instead of parsing a list, should be pref= erred. Scripts, that use /proc/cpuinfo to determine if the current CPU is "compliant" with defined microarchitecture levels like x86-64-v2 will false= ly claim the CPU is incapable of modern CPU instructions when "lahf_lm" is mis= sing in that flags list. This can prevent some docker containers from starting or build scripts to c= reate unoptimized binaries. Admittably, this is more a small inconvenience than a severe bug in the ker= nel 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 r= dtscp lm rep_good nopl cpuid extd_apicid tsc_known_freq pni pclmulqdq ssse3 fma cx16 sse4_1 sse4_2 x2apic movbe p= opcnt 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 9413fb767c6a7..be378b44ca35f 100644 --- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -825,7 +825,7 @@ static void init_amd_k8(struct cpuinfo_x86 *c) * (model =3D 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 &=3D ~BIT_64(32); --=20 2.39.5