From nobody Tue Feb 10 04:23:51 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 35A7B1DF73C; Tue, 29 Apr 2025 17:10:10 +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=1745946610; cv=none; b=lwd568FxJQOTJ/YBZ9LIDYZ+zAscZnIylY4x/Maw+TW02mQrbXLpFK4h1vVPKyuxvUrdStO8u3cti1E2fQv9O4RORYZKsF4kGl/Vmz2DOHRakRIUfQ9+F7W3NL+zbxtisDKGvFMdlzL19B9T5S2/fBSbwOibY5AmuN7W1UJF5fM= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745946610; c=relaxed/simple; bh=lADPbhiKG0z3i47u2cGgCB0Xa+zoWFmODShud75S2zg=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=NGubbKUaCDP1I6ZsIG5aFjXJerYvn3jMhbnPQBlt1XPyEuHWechX/Yf4SjI2/M1vnc7eb2UQRaBk7nvkDuF51VJmHNRlhppS177/GXhQYQJIIcHLqbMYDIFeqxdNHqnCUw1fd/dr68Io6Ca//iSF78ZEbMEnOViUw06gEqYjKV0= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Kh7O59n7; 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="Kh7O59n7" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A909EC4CEE3; Tue, 29 Apr 2025 17:10:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1745946610; bh=lADPbhiKG0z3i47u2cGgCB0Xa+zoWFmODShud75S2zg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Kh7O59n7ztMuvMcvFGSY/DzhpEmkBJOfs8Ol101wAzzn5rztG+Y1GnzkRQSNSWIgK h9hjr1SZK+xQ8u/R3OPC2X1VcNa8whOLOBL1r+VRjT+78GaHV/aZ9rIJuSItw0+Dy3 Hh47wSIyCfYVx7ht9fE2ZjDuUHCq3fIP5NbniLoI= 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 5.10 012/286] 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 18:38:36 +0200 Message-ID: <20250429161108.358465874@linuxfoundation.org> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20250429161107.848008295@linuxfoundation.org> References: <20250429161107.848008295@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 5.10-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 c10f7dcaa7b7c..5f0bdb53b0067 100644 --- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -839,7 +839,7 @@ 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