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Revert "kasan: drop skip_kasan_poison variable in free_pages_prepare"
This reverts commit 487a32e. should_skip_kasan_poison() reads the PG_skip_kasan_poison flag from page->flags. However, this line of code in free_pages_prepare(): page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP; clears most of page->flags, including PG_skip_kasan_poison, before calling should_skip_kasan_poison(), which meant that it would never return true as a result of the page flag being set. Therefore, fix the code to call should_skip_kasan_poison() before clearing the flags, as we were doing before the reverted patch. This fixes a measurable performance regression introduced in the reverted commit, where munmap() takes longer than intended if HW tags KASAN is supported and enabled at runtime. Without this patch, we see a single-digit percentage performance regression in a particular mmap()-heavy benchmark when enabling HW tags KASAN, and with the patch, there is no statistically significant performance impact when enabling HW tags KASAN. Link: https://lkml.kernel.org/r/[email protected] Fixes: 487a32e ("kasan: drop skip_kasan_poison variable in free_pages_prepare") Link: https://linux-review.googlesource.com/id/Ic4f13affeebd20548758438bb9ed9ca40e312b79 Signed-off-by: Peter Collingbourne <[email protected]> Reviewed-by: Andrey Konovalov <[email protected]> Cc: Andrey Ryabinin <[email protected]> Cc: Catalin Marinas <[email protected]> [arm64] Cc: Evgenii Stepanov <[email protected]> Cc: Vincenzo Frascino <[email protected]> Cc: Will Deacon <[email protected]> Cc: <[email protected]> [6.1] Signed-off-by: Andrew Morton <[email protected]>
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