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[96.255.20.138]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-87cf51fcd39sm9355186d6.6.2025.10.17.19.40.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 17 Oct 2025 19:40:18 -0700 (PDT) From: Gregory Price To: x86@kernel.org Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, peterz@infradead.org, mario.limonciello@amd.com, riel@surriel.com, yazen.ghannam@amd.com, me@mixaill.net, kai.huang@intel.com, sandipan.das@amd.com, darwi@linutronix.de, stable@vger.kernel.org Subject: [PATCH v2] x86/amd: Disable RDSEED on AMD Zen5 because of an error. Date: Fri, 17 Oct 2025 22:40:10 -0400 Message-ID: <20251018024010.4112396-1-gourry@gourry.net> X-Mailer: git-send-email 2.51.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Under unknown conditions, Zen5 chips running rdseed can produce (val=3D0,CF=3D1) over 10% of the time (when rdseed is successful). CF=3D1 indicates success, while val=3D0 is typically only produced when rdseed fails (CF=3D0). This suggests there is a bug which causes rdseed to silently fail. This was reproduced reliably by launching 2-threads per available core, 1-thread per for hamming on RDSEED, and 1-thread per core collectively eating and hammering on ~90% of memory. This was observed on more than 1 Zen5 model, so it should be disabled for all of Zen5 until/unless a comprehensive blacklist can be built. Cc: stable@vger.kernel.org Signed-off-by: Gregory Price --- arch/x86/kernel/cpu/amd.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c index 5398db4dedb4..1af30518d3e7 100644 --- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -1037,6 +1037,10 @@ static void init_amd_zen4(struct cpuinfo_x86 *c) =20 static void init_amd_zen5(struct cpuinfo_x86 *c) { + /* Disable RDSEED on AMD Turin because of an error. */ + clear_cpu_cap(c, X86_FEATURE_RDSEED); + msr_clear_bit(MSR_AMD64_CPUID_FN_7, 18); + pr_emerg("RDSEED is not reliable on this platform; disabling.\n"); } =20 static void init_amd(struct cpuinfo_x86 *c) --=20 2.51.0