From: Peter Collingbourne <pcc@xxxxxxxxxx> commit f446883d12b8bfa486f7c98d403054d61d38c989 upstream. 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@xxxxxxxxxx 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@xxxxxxxxxx> Reviewed-by: Andrey Konovalov <andreyknvl@xxxxxxxxx> Cc: Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx> Cc: Catalin Marinas <catalin.marinas@xxxxxxx> [arm64] Cc: Evgenii Stepanov <eugenis@xxxxxxxxxx> Cc: Vincenzo Frascino <vincenzo.frascino@xxxxxxx> Cc: Will Deacon <will@xxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> [6.1] Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- mm/page_alloc.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1402,6 +1402,7 @@ static __always_inline bool free_pages_p unsigned int order, bool check_free, fpi_t fpi_flags) { int bad = 0; + bool skip_kasan_poison = should_skip_kasan_poison(page, fpi_flags); bool init = want_init_on_free(); VM_BUG_ON_PAGE(PageTail(page), page); @@ -1476,7 +1477,7 @@ static __always_inline bool free_pages_p * With hardware tag-based KASAN, memory tags must be set before the * page becomes unavailable via debug_pagealloc or arch_free_page. */ - if (!should_skip_kasan_poison(page, fpi_flags)) { + if (!skip_kasan_poison) { kasan_poison_pages(page, order, init); /* Memory is already initialized if KASAN did it internally. */
