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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49fbf415058sm34707795e9.0.2026.09.17.02.14.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 17 Sep 2026 02:14:56 -0700 (PDT) Date: Thu, 17 Sep 2026 10:14:55 +0100 From: David Laight To: "Chang S. Bae" Cc: linux-kernel@vger.kernel.org, x86@kernel.org, tglx@kernel.org, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, andrew.cooper3@citrix.com, arjan.van.de.ven@intel.com, sohil.mehta@intel.com, stable@vger.kernel.org Subject: Re: [PATCH v3] x86/microcode/intel: Reject problematic loading on Granite Rapids systems Message-ID: <20260917101455.3e1ac9a5@pumpkin> In-Reply-To: <20260916225939.1144524-1-chang.seok.bae@intel.com> References: <20260908223209.916758-1-chang.seok.bae@intel.com> <20260916225939.1144524-1-chang.seok.bae@intel.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) 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=US-ASCII Content-Transfer-Encoding: 7bit On Wed, 16 Sep 2026 22:59:39 +0000 "Chang S. Bae" wrote: > Microcode updates can usually jump revisions. However, there is an > erratum on Granite Rapids systems. If they "jump over" revision > 0x1000405, they result in #MC. Avoid it. A probably silly question. Is it valid to downgrade microcode? David > > Signed-off-by: Chang S. Bae > Reviewed-by: Dave Hansen > Cc: > --- > V2 -> V3: > * Shorten the changelog and rename the function (Boris) > * Reduce the code comment (Dave) > * Allow 0x1000405 loading. Thanks to Andrew, this fix got attention. > * Collect Dave review tag. Thanks, Dave! > > Note: > * GNR98 currently describes loading 0x1000405 itself is unsafe, but it > will be updated to say okay with that. I will watch out the GNR98 > changes. > * Jumping from < 0x1000380 to 0x1000405 was identified as an issue, but > 0x1000380 is the first revision as GNR products. So loading 0x1000405 > in production systems should be okay. > --- > arch/x86/kernel/cpu/microcode/intel.c | 26 ++++++++++++++++++++++++++ > 1 file changed, 26 insertions(+) > > diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c > index 1142183c950c..30a22388d4b1 100644 > --- a/arch/x86/kernel/cpu/microcode/intel.c > +++ b/arch/x86/kernel/cpu/microcode/intel.c > @@ -309,6 +309,26 @@ static void save_microcode_patch(struct microcode_intel *patch) > pr_err("Unable to allocate microcode memory size: %u\n", size); > } > > +static bool revision_is_safe(struct cpu_signature *sig, u32 rev) > +{ > + u32 vfm = IFM(x86_family(sig->sig), x86_model(sig->sig)); > + > + /* > + * Erratum GNR98 can cause #MC's if "jumping over" revision 0x1000405. > + * Avoid the jumps. > + */ > + if (vfm == INTEL_GRANITERAPIDS_X && > + x86_stepping(sig->sig) == 1 && > + sig->pf & 0x95 && > + sig->rev < 0x1000405 && > + rev > 0x1000405) { > + pr_err_once("Erratum GNR98: skipping revision 0x%x.\n", rev); > + return false; > + } > + > + return true; > +} > + > /* Scan blob for microcode matching the boot CPUs family, model, stepping */ > static __init struct microcode_intel *scan_microcode(void *data, size_t size, > struct ucode_cpu_info *uci, > @@ -330,6 +350,9 @@ static __init struct microcode_intel *scan_microcode(void *data, size_t size, > if (!intel_find_matching_signature(data, &uci->cpu_sig)) > continue; > > + if (!revision_is_safe(&uci->cpu_sig, mc_header->rev)) > + continue; > + > /* > * For saving the early microcode, find the matching revision which > * was loaded on the BSP. > @@ -878,6 +901,9 @@ static enum ucode_state parse_microcode_blobs(int cpu, struct iov_iter *iter) > if (!intel_find_matching_signature(mc, &uci->cpu_sig)) > continue; > > + if (!revision_is_safe(&uci->cpu_sig, mc_header.rev)) > + continue; > + > is_safe = ucode_validate_minrev(&mc_header); > if (force_minrev && !is_safe) > continue;