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Wysocki" , Len Brown , Ard Biesheuvel , Jeremy Linton , Catalin Marinas , "linux-acpi@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] ACPI/PPTT: fix off-by-one error Thread-Topic: [PATCH] ACPI/PPTT: fix off-by-one error Thread-Index: AQHbv1xqHHdPuyThMkGwcKsDIcT/2Q== Date: Wed, 7 May 2025 14:29:17 +0000 Message-ID: <20250507-petit-capri-debaa30d@mheyne-amazon> References: <20250506-draco-taped-15f475cd@mheyne-amazon> <20250506-shapeless-merciful-inchworm-7bfdb4@sudeepholla> <20250506-dialog-57th-c4e70064@mheyne-amazon> <20250507-mysterious-emu-of-fertility-951c69@sudeepholla> <20250507-blend-revel-3d94099b@mheyne-amazon> <20250507-quantum-solid-ibex-218f1b@sudeepholla> <20250507-autumn-phrase-4a1eddef@mheyne-amazon> <20250507-divergent-lori-from-pluto-71daee@sudeepholla> In-Reply-To: <20250507-divergent-lori-from-pluto-71daee@sudeepholla> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: Content-Type: text/plain; charset="us-ascii" Content-ID: <4F4607C6B6FDBE46A5D43E61104AA72E@amazon.com> Precedence: bulk X-Mailing-List: linux-acpi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable On Wed, May 07, 2025 at 01:56:53PM +0100, Sudeep Holla wrote: > On Wed, May 07, 2025 at 12:42:14PM +0000, Heyne, Maximilian wrote: > > On Wed, May 07, 2025 at 01:30:53PM +0100, Sudeep Holla wrote: > > > On Wed, May 07, 2025 at 11:56:48AM +0000, Heyne, Maximilian wrote: > > > > On Wed, May 07, 2025 at 12:52:18PM +0100, Sudeep Holla wrote: > > > > > = > > > > > Just to understand, this node is absolutely processor node with no > > > > > private resources ? I find it hard to trust this as most of the C= PUs > > > > > do have L1 I&D caches. If they were present the table can't abrup= tly end > > > > > like this. > > > > = > > > > Yes looks like it. In our case the ACPI subtable has length 0x14 wh= ich is > > > > exactly sizeof(acpi_pptt_processor). > > > > = > > > = > > > OK, this seem like it is emulated platform with no private resources = as > > > it is specified in the other similar patch clearly(QEMU/VM). So this > > > doesn't match real platforms. Your PPTT is wrong if it is real hardwa= re > > > platform as you must have private resources. > > > = > > > Anyways if we allow emulation to present CPUs without private resourc= es > > > we may have to consider allowing this as the computed pointer will ma= tch > > > the table end. > > = > > Is there a need by the ACPI specification that the Cache information > > must come after the processor information? Because on our platform there > > is Cache and it's described but at a different location seemingly. It > > looks like caches are described first and then the CPUs. > > > = > That is fine but you must have reference to those caches in the processor > node and the length of the node won't be 0x14 in that case and you should= n't > hit this issue. So if this is real platform, then yes I am must say you > PPTT is wrong especially if there are caches in the table as you say just > that processor nodes are not pointing to them correctly then ? The ACPI tables in our case describe a core first which references the cache as private resource and then a thread whose parent is the core but this doesn't have a private resource. This is how it looks like: [C8Eh 3214 1] Subtable Type : 00 [Processor Hierarchy Node] [C8Fh 3215 1] Length : 1C [C90h 3216 2] Reserved : 0000 [C92h 3218 4] Flags (decoded below) : 00000002 Physical package : 0 ACPI Processor ID valid : 1 Processor is a thread : 0 Node is a leaf : 0 Identical Implementation : 0 [C96h 3222 4] Parent : 000000A2 [C9Ah 3226 4] ACPI Processor ID : 0000003F [C9Eh 3230 4] Private Resource Number : 00000002 [CA2h 3234 4] Private Resource : 00000072 [CA6h 3238 4] Private Resource : 0000008A [CAAh 3242 1] Subtable Type : 00 [Processor Hierarchy Node] [CABh 3243 1] Length : 14 [CACh 3244 2] Reserved : 0000 [CAEh 3246 4] Flags (decoded below) : 0000000E Physical package : 0 ACPI Processor ID valid : 1 Processor is a thread : 1 Node is a leaf : 1 Identical Implementation : 0 [CB2h 3250 4] Parent : 00000C8E [CB6h 3254 4] ACPI Processor ID : 0000003F [CBAh 3258 4] Private Resource Number : 00000000 > = > > I can try to drill even deeper here if you insist. As said I'm no > > subject matter expert here. But is there something obviously wrong with > > my patch or would it be ok to just take it? > > > = > Yes you much check your PPTT if it is real hardware platform. I am OK > with the change in terms of QEMU or VM. You may need to reword commit > message a bit. I will respond separately. > = > -- = > Regards, > Sudeep Amazon Web Services Development Center Germany GmbH Tamara-Danz-Str. 13 10243 Berlin Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss Eingetragen am Amtsgericht Charlottenburg unter HRB 257764 B Sitz: Berlin Ust-ID: DE 365 538 597