From nobody Sun Feb 8 18:24:26 2026 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (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 016C28BEC; Thu, 27 Feb 2025 21:24:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740691497; cv=none; b=HmQTi9tQNl+6WdrNI5CV9N5O6BkSttZM0Pq3u47UVYfcXPxhCW/vURa5BXB0d2xDA/kaUUa5GgCRT9U4lAvqsdh6FPNv6BYIPnpH/0lcC7pwMOZQZvn/c8/Lzn05n37IZIAQ/+tIh0hlIvTNphEmAvSY5z2JjqF+lWgaymnh2x8= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740691497; c=relaxed/simple; bh=I7Gw+VOrI81yKKKEn1hv//pEIL9LNwWod+qYpXQUf9Q=; h=Date:From:To:Subject:Cc:MIME-Version:Message-ID:Content-Type; b=H9Y0zEcH51nE1W4gJv4o0DitRzOdNd3bOIWhLY+iv/D6bXmjbZgKSGNfzJ3o1CQ1M0qL1vxyUOsi8/8zdmEfTda1jDLakXHkNxC8m+W5MI/rAWwNtutrz8c7LvW93l/Mk8+igtIM9bl9KV0FSZ6TUJNKu0I528eqG5LGQwl1X4Y= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=KfLOkzEc; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=h6j0FYMj; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="KfLOkzEc"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="h6j0FYMj" Date: Thu, 27 Feb 2025 21:24:40 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1740691492; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=9pP9b9kojON7jgAl1zqDNk5ddQhlUEqyQo91wqw5eHo=; b=KfLOkzEci080xPMVcz3Jh91nB78XZJHH/sL9C9FHW+LoX6YmmShcv0xoWSKkS/Ar2AI3EW 8G/3d0WxpwrrsNy2LPKobYYZBRyayvw1CZk2aFp35Q5OHYRNoE93w9MXd04LJmDt8Ga93R FWE3Jv3GOiIKsA4CpwfafqiNhXp0e5Rf5thn5Zz6wUzmwkyr0EnheSklSp/E5jAHvF4mbc KdmjoVPNSWUE+IZJQVX8/7nNT1GvYLPoQJttfnjGatJMQBqXZ5dc6fcvBfLaHraqeOaeoU H2JZqYENAosy8u7NVSoB2IHCPFfJldPPy17Rgxm3lW+Bz1rzbnm21DA7kvrhVw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1740691492; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=9pP9b9kojON7jgAl1zqDNk5ddQhlUEqyQo91wqw5eHo=; b=h6j0FYMjcD8vCIU91p5qvwqYgTKv9gdOSIeiQgC9jKnRpXfmfVe/Q0Gpn3SODUbFKDOTkJ SmHi5G5Syv7i6lBQ== From: "tip-bot2 for Max Grobecker" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: x86/cpu] x86/cpu: Don't clear X86_FEATURE_LAHF_LM flag in init_amd_k8() on AMD when running in a virtual machine Cc: Max Grobecker , Ingo Molnar , linux-kernel@vger.kernel.org, Borislav Petkov , x86@kernel.org Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-ID: <174069148027.10177.17527893236219214276.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Precedence: bulk Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable The following commit has been merged into the x86/cpu branch of tip: Commit-ID: 1ec6ddc0d9857b56f1cb3d014395eee6a86923d6 Gitweb: https://git.kernel.org/tip/1ec6ddc0d9857b56f1cb3d014395eee6a= 86923d6 Author: Max Grobecker AuthorDate: Thu, 27 Feb 2025 21:45:05 +01:00 Committer: Ingo Molnar CommitterDate: Thu, 27 Feb 2025 22:07:28 +01:00 x86/cpu: Don't clear X86_FEATURE_LAHF_LM flag in init_amd_k8() on AMD when = running in a virtual machine 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. ] Signed-off-by: Max Grobecker Signed-off-by: Ingo Molnar Cc: linux-kernel@vger.kernel.org Cc: Borislav Petkov --- arch/x86/kernel/cpu/amd.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c index 54194f5..c1f0a5f 100644 --- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -631,8 +631,11 @@ static void init_amd_k8(struct cpuinfo_x86 *c) * Some BIOSes incorrectly force this feature, but only K8 revision D * (model =3D 0x14) and later actually support it. * (AMD Erratum #110, docId: 25759). + * Only clear capability flag if we're running on baremetal, + * as we might see a wrong model ID as a guest kernel. In such a case, + * we can safely assume we're not affected by this erratum. */ - 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);