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authorPeter Collingbourne <pcc@google.com>2023-03-09 20:29:13 -0800
committerAndrew Morton <akpm@linux-foundation.org>2023-03-23 17:18:34 -0700
commitf446883d12b8bfa486f7c98d403054d61d38c989 (patch)
tree6307da53bae2e30cb0378287015cf244884823ee /.mailmap
parentcc2a978d28422ca957d14cb25caa72e25c45be1d (diff)
Revert "kasan: drop skip_kasan_poison variable in free_pages_prepare"
This reverts commit 487a32ec24be819e747af8c2ab0d5c515508086a. 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/20230310042914.3805818-2-pcc@google.com Fixes: 487a32ec24be ("kasan: drop skip_kasan_poison variable in free_pages_prepare") Link: https://linux-review.googlesource.com/id/Ic4f13affeebd20548758438bb9ed9ca40e312b79 Signed-off-by: Peter Collingbourne <pcc@google.com> Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com> Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com> Cc: Catalin Marinas <catalin.marinas@arm.com> [arm64] Cc: Evgenii Stepanov <eugenis@google.com> Cc: Vincenzo Frascino <vincenzo.frascino@arm.com> Cc: Will Deacon <will@kernel.org> Cc: <stable@vger.kernel.org> [6.1] Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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