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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: Rekj76aeBwb4Kh0aUf577OuIKgi61ZWLEGTwoCmPopwP0chj5MlJlDhzK58YGIkBqW7eCWubNfWldUlj14dc5V4DG9GEx+2t5VA9A/Y6/66vVKMEAgzhA97+koRoVub5YVmtbrEGME+ZI1rmJGiPLA+4Y+PkZ82zQ/G5NdvblFGC2sSyF40YWdbnxNkOSq9rGOHLoEDyw0osTiDIxbUS9zosLfk4Q9CocR7UIOf7Schh8uPBAABOoCCHMgWCmRYxdssbG3p03pqwpJj9OQNUwtZo/krDWrtZKeLqPdM6x45oHE03jwAze7CdTZAq4yBtzRkR/YCwftTAH4bkVkdESEwJmsDC9wXAoHKJrktBjkxaDL/XrfF+1pEHkDYczwgVmFyATmDxTLCsm7CwBLd0rT8DRl1ovTRk0M3CuEPPEHmezsFnPpl4vkUtb9TlIgpg X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 29 Sep 2026 12:29:40.1239 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: a82a13c5-29d2-4fe7-0127-08df1e25554b X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[4.158.2.129];Helo=[outbound-uk1.az.dlp.m.darktrace.com] X-MS-Exchange-CrossTenant-AuthSource: AMS0EPF0000056A.eurprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: GV2PR08MB763876 Hi, On 2026. 09. 23. 19:31, Jonathan Cameron wrote: > On Wed, 23 Sep 2026 10:21:15 +0200 > Bence Csókás wrote: > >> Hi, >> >> On 2026. 09. 23. 4:18, Andrew Morton wrote: >>> On Tue, 22 Sep 2026 09:29:31 +0200 Bence Csokas wrote: >>> >>>> Currently, if there are no registered handlers, >>>> cpu_cache_invalidate_memregion() returns 0. Callers are expected to check >>>> cpu_cache_has_invalidate_memregion() and return -ENXIO themselves, instead >>>> of calling this function. If a caller forgets to do this, they may >>>> erroneously think the operation succeeded. This is in contrast to x86, >>>> where cpu_cache_invalidate_memregion() itself checks if the operation is >>>> supported, and returns -ENXIO if it is not. >>> >>> Do you expect any callers to be altered as a result of this change? >>> >>> If so, full details would be helpful. >> >> Current callers, not necessarily. Future callers, maybe. > > There is a race condition if someone unbinds the handlers that might > expose an error after this (correctly) when it didn't before. > > In general that race exists in the setup path as well because we don't have > any way to know 'how many' devices to expect with assumption being > they have all turned up if any have. Not great, but short of adding > something to the firmware specification there wasn't a solution and > that process would be slow. We can revisit that if it becomes a problem > in practice. > > >> >> Presently, as far as I see, there are 2 consumers: CXL and NVDIMM, with >> 3 call sites in total. >> >> 2 of these call sites [1] [2] are in the form of: >> >> if (!has_invalidate()) { >> if (TEST) >> return 0; >> return -ENXIO; >> } >> invalidate(); >> >> These types of call sites can stay as-is. >> >> The remaining one [3] is in a void function, and in the form: >> >> if (has_invalidate()) >> invalidate(); >> >> Lastly, while not a consumer, here's what x86 [4] does. It's possible a >> future caller will want to replicate this: >> >> if (!has_invalidate()) >> return -ENXIO; >> invalidate(); >> >> These types of call sites can do away with calling has_invalidate() >> going forward. > > I'd be against any callers doing that as would rely on future implementations > of the interface. No support vs got an error tend to need different handling > and relying on particular error codes is likely to bite us eventually. Yes, if the callers need to handle these separate cases (as in call sites [1] and [2]), then for sure keep the existing logic. But some call sites may not need to handle these cases differently, and will simply return -ENXIO if they find no support. In those cases, they may simply do return cpu_cache_invalidate_memregion(); (I now realize that I forgot the `return` in my previous post, sorry for the confusion.) But at the end of the day, I don't have any strong opinion on this. For now, current callers can stay as-is, and for future callers, we'll decide in that thread. > Jonathan > >> >> [1] >> https://elixir.bootlin.com/linux/v7.3-rc3/source/drivers/cxl/core/region.c#L242 >> [2] >> https://elixir.bootlin.com/linux/v7.3-rc3/source/drivers/nvdimm/region_devs.c#L93 >> [3] >> https://elixir.bootlin.com/linux/v7.3-rc3/source/drivers/nvdimm/region.c#L113 >> [4] >> https://elixir.bootlin.com/linux/v7.3-rc3/source/arch/x86/mm/pat/set_memory.c#L372 >> >> Bence > So the consensus is that my hunch was correct, and this is something to address? Should I resubmit this patch as non-RFC then? Bence