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b=CksvXvxhab9U4JbykfOUrtCcbLOZdQ/5tE0zMsXnKVWD9ybEiMXEZXhkcIdTMpcRB4ArewzD11+EC7nRPCnaU2sWLWnp/JJjCmyknZOdV+RAQ9/VBtyT/vIu1AV+9vnWZgM/TTHGibuX4U0C13w8jgHfkqevWOGHYKaHkvvVKUs= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=citrix.com; Message-ID: <6a54806f-061b-4b76-b42d-6fa5b54581e4@citrix.com> Date: Tue, 8 Sep 2026 11:08:26 +0100 User-Agent: Mozilla Thunderbird Cc: Andrew Cooper , =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= , Teddy Astie , Xen-devel Subject: Re: [PATCH v2] x86/ucode: Work around Granite Rapids erraturm GNR98 To: Jan Beulich References: <20260907213231.3159241-1-andrew.cooper3@citrix.com> Content-Language: en-GB From: Andrew Cooper Autocrypt: addr=andrew.cooper3@citrix.com; keydata= xsFNBFLhNn8BEADVhE+Hb8i0GV6mihnnr/uiQQdPF8kUoFzCOPXkf7jQ5sLYeJa0cQi6Penp VtiFYznTairnVsN5J+ujSTIb+OlMSJUWV4opS7WVNnxHbFTPYZVQ3erv7NKc2iVizCRZ2Kxn srM1oPXWRic8BIAdYOKOloF2300SL/bIpeD+x7h3w9B/qez7nOin5NzkxgFoaUeIal12pXSR Q354FKFoy6Vh96gc4VRqte3jw8mPuJQpfws+Pb+swvSf/i1q1+1I4jsRQQh2m6OTADHIqg2E ofTYAEh7R5HfPx0EXoEDMdRjOeKn8+vvkAwhviWXTHlG3R1QkbE5M/oywnZ83udJmi+lxjJ5 YhQ5IzomvJ16H0Bq+TLyVLO/VRksp1VR9HxCzItLNCS8PdpYYz5TC204ViycobYU65WMpzWe LFAGn8jSS25XIpqv0Y9k87dLbctKKA14Ifw2kq5OIVu2FuX+3i446JOa2vpCI9GcjCzi3oHV e00bzYiHMIl0FICrNJU0Kjho8pdo0m2uxkn6SYEpogAy9pnatUlO+erL4LqFUO7GXSdBRbw5 gNt25XTLdSFuZtMxkY3tq8MFss5QnjhehCVPEpE6y9ZjI4XB8ad1G4oBHVGK5LMsvg22PfMJ ISWFSHoF/B5+lHkCKWkFxZ0gZn33ju5n6/FOdEx4B8cMJt+cWwARAQABzSlBbmRyZXcgQ29v cGVyIDxhbmRyZXcuY29vcGVyM0BjaXRyaXguY29tPsLBegQTAQgAJAIbAwULCQgHAwUVCgkI CwUWAgMBAAIeAQIXgAUCWKD95wIZAQAKCRBlw/kGpdefoHbdD/9AIoR3k6fKl+RFiFpyAhvO 59ttDFI7nIAnlYngev2XUR3acFElJATHSDO0ju+hqWqAb8kVijXLops0gOfqt3VPZq9cuHlh IMDquatGLzAadfFx2eQYIYT+FYuMoPZy/aTUazmJIDVxP7L383grjIkn+7tAv+qeDfE+txL4 SAm1UHNvmdfgL2/lcmL3xRh7sub3nJilM93RWX1Pe5LBSDXO45uzCGEdst6uSlzYR/MEr+5Z JQQ32JV64zwvf/aKaagSQSQMYNX9JFgfZ3TKWC1KJQbX5ssoX/5hNLqxMcZV3TN7kU8I3kjK mPec9+1nECOjjJSO/h4P0sBZyIUGfguwzhEeGf4sMCuSEM4xjCnwiBwftR17sr0spYcOpqET ZGcAmyYcNjy6CYadNCnfR40vhhWuCfNCBzWnUW0lFoo12wb0YnzoOLjvfD6OL3JjIUJNOmJy RCsJ5IA/Iz33RhSVRmROu+TztwuThClw63g7+hoyewv7BemKyuU6FTVhjjW+XUWmS/FzknSi dAG+insr0746cTPpSkGl3KAXeWDGJzve7/SBBfyznWCMGaf8E2P1oOdIZRxHgWj0zNr1+ooF /PzgLPiCI4OMUttTlEKChgbUTQ+5o0P080JojqfXwbPAyumbaYcQNiH1/xYbJdOFSiBv9rpt TQTBLzDKXok86M7BTQRS4TZ/ARAAkgqudHsp+hd82UVkvgnlqZjzz2vyrYfz7bkPtXaGb9H4 Rfo7mQsEQavEBdWWjbga6eMnDqtu+FC+qeTGYebToxEyp2lKDSoAsvt8w82tIlP/EbmRbDVn 7bhjBlfRcFjVYw8uVDPptT0TV47vpoCVkTwcyb6OltJrvg/QzV9f07DJswuda1JH3/qvYu0p vjPnYvCq4NsqY2XSdAJ02HrdYPFtNyPEntu1n1KK+gJrstjtw7KsZ4ygXYrsm/oCBiVW/OgU g/XIlGErkrxe4vQvJyVwg6YH653YTX5hLLUEL1NS4TCo47RP+wi6y+TnuAL36UtK/uFyEuPy wwrDVcC4cIFhYSfsO0BumEI65yu7a8aHbGfq2lW251UcoU48Z27ZUUZd2Dr6O/n8poQHbaTd 6bJJSjzGGHZVbRP9UQ3lkmkmc0+XCHmj5WhwNNYjgbbmML7y0fsJT5RgvefAIFfHBg7fTY/i kBEimoUsTEQz+N4hbKwo1hULfVxDJStE4sbPhjbsPCrlXf6W9CxSyQ0qmZ2bXsLQYRj2xqd1 bpA+1o1j2N4/au1R/uSiUFjewJdT/LX1EklKDcQwpk06Af/N7VZtSfEJeRV04unbsKVXWZAk uAJyDDKN99ziC0Wz5kcPyVD1HNf8bgaqGDzrv3TfYjwqayRFcMf7xJaL9xXedMcAEQEAAcLB XwQYAQgACQUCUuE2fwIbDAAKCRBlw/kGpdefoG4XEACD1Qf/er8EA7g23HMxYWd3FXHThrVQ HgiGdk5Yh632vjOm9L4sd/GCEACVQKjsu98e8o3ysitFlznEns5EAAXEbITrgKWXDDUWGYxd pnjj2u+GkVdsOAGk0kxczX6s+VRBhpbBI2PWnOsRJgU2n10PZ3mZD4Xu9kU2IXYmuW+e5KCA vTArRUdCrAtIa1k01sPipPPw6dfxx2e5asy21YOytzxuWFfJTGnVxZZSCyLUO83sh6OZhJkk b9rxL9wPmpN/t2IPaEKoAc0FTQZS36wAMOXkBh24PQ9gaLJvfPKpNzGD8XWR5HHF0NLIJhgg 4ZlEXQ2fVp3XrtocHqhu4UZR4koCijgB8sB7Tb0GCpwK+C4UePdFLfhKyRdSXuvY3AHJd4CP 4JzW0Bzq/WXY3XMOzUTYApGQpnUpdOmuQSfpV9MQO+/jo7r6yPbxT7CwRS5dcQPzUiuHLK9i nvjREdh84qycnx0/6dDroYhp0DFv4udxuAvt1h4wGwTPRQZerSm4xaYegEFusyhbZrI0U9tJ B8WrhBLXDiYlyJT6zOV2yZFuW47VrLsjYnHwn27hmxTC/7tvG3euCklmkn9Sl9IAKFu29RSo d5bD8kMSCYsTqtTfT6W4A3qHGvIDta3ptLYpIAOD2sY3GYq2nf3Bbzx81wZK14JdDDHUX2Rs 6+ahAA== In-Reply-To: Content-Type: text/plain; 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>> } >> >> +static bool microcode_safe_to_load(const struct microcode_patch *mc) >> +{ >> + struct cpu_signature *cpu_sig = &this_cpu(cpu_sig); >> + >> + /* >> + * Treat pre-production as always safe - anyone using pre-production >> + * microcode knows what they are doing, and can keep any resulting pieces. >> + */ >> + if ( (int)cpu_sig->rev < 0 || mc->rev < 0 ) >> + return true; >> + >> + /* >> + * GNR98 states that Granite Rapids systems hang when loading new ucode on >> + * sufficiently old firmware. GNR101 retroactively declares that one >> + * ucode had incorrect min_rev fields, in light of discovering GNR98. > We still have no min_rev field, so imo a reference to it wants some > clarification. No, I don't think so.  The fact Xen has no min_rev field (yet) has no baring on the wording of GNR101. This patch stops Xen hanging with the real ucode which has existed in the world for 6 months. I am still waiting on Intel to publish new blobs (including corrected min_rev fields) before the multi-hop update can be made to work.  I have no ETA on this. > Really I first meant to ask why there's no use of that field, > to merely make that one exception. > >> + * Both are incomplete statements of the problem. >> + * >> + * At the time of writing (August 2026), the believed safe sequence is: >> + * 0x01000370 -> [0x01000380...0x010003f3] -> 0x01000405 -> any later >> + * >> + * Disallow known-unsafe loads while permitting believed-safe loads. For >> + * GNR, this allows multi-hop loading to get up to the latest. >> + */ >> + if ( boot_cpu_data.vfm == INTEL_GRANITERAPIDS_X && >> + boot_cpu_data.stepping == 1 && (cpu_sig->pf & 0x95) && >> + ((cpu_sig->rev < 0x01000380 && mc->rev >= 0x01000405) || > This is odd: The lhs of && uses the lower bound of the inner permitted > range, while the rhs of the && doesn't use the upper one. If it's intended > that way, I think this also needs clarifying in the comment. Otherwise imo > lhs and rhs better would be consistent in this regard. It is intentional.  Furthermore, it is the only coherent way of expressing the sequence as given. I'm not writing a comment explaining why it's a good idea to use the same boundary numerals between the comment and the code.  It goes without saying. I'm also not interested about pureness concerns about inner vs outer bounds.  I can't see a change here that won't make it worse. > >> + (cpu_sig->rev < 0x01000405 && mc->rev > 0x01000405)) ) > This one, otoh, fully matches the comment. > >> + { >> + printk_once(XENLOG_WARNING >> + "microcode: Granite Rapids erratum GNR98 detected. Skipping ucode 0x%08x\n" >> + "microcode: Firmware update recommended\n", mc->rev); > I think a 2nd XENLOG_WARNING is wanted after the inner \n (or none at all, > to use the default for both). Fine, fixed up locally. ~Andrew