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charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/10/26 12:26, Yuanhe Shu wrote: While the file touches highmem.h, this really isn't about highmem at all, right? This really affects any architecture except the ones that define copy_mc_to_kernel (x86+powerpc). Or am I missing something? Would be good to clarify that. > The !copy_mc fallbacks of copy_mc_user_highpage() and > copy_mc_highpage() return 0 after a plain copy. With PG_hwpoison > set while the data stays readable, there is no fault to recover > from: the copy completes, the destination folio carries no poison > marker, and the poison is consumed silently. > > Check the source page with is_page_hwpoison() in both fallbacks, > before the copy, and return PAGE_SIZE, the not-copied-bytes > convention of the real copy_mc paths, so the callers take their > existing error paths. On archs with copy_mc this code does not > compile. > > Measured on arm64, where the fallback code compiles: a > kernel-space microbenchmark measures 90.00 ns per copy before the > patch and 90.71 ns after, 0.8% of the copy itself. CCing Catalin. I'm surprised that arm64 cannot recover from a copy from a hwpoisoned page. -- Cheers, David