From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 99C9B8476 for ; Tue, 28 Mar 2023 14:54:50 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1F6FBC433D2; Tue, 28 Mar 2023 14:54:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1680015290; bh=stprJ4Ok6iOxRao5KYE4oaQuciwWQTRlYZK94PRhwNI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=M9WxxO8lbzeRu4T7vPeJjoTl0jWdywHgz9gzx36yuV4ylRkIr/ojBwSVg0hY2fO/K 1bz4i+AJYqVWpjdiFh+VXKnvuzc8sgFRuSVY+9TZt+v3oSz3+dqbn6BaedF+gBQ9n/ vJVklK85Tbp73Bjv1Mqo5A/NtF/8Jlr0Bnxb1u/g= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Peter Collingbourne , Andrey Konovalov , Andrey Ryabinin , Evgenii Stepanov , Vincenzo Frascino , Will Deacon , Andrew Morton , Catalin Marinas Subject: [PATCH 6.2 205/240] Revert "kasan: drop skip_kasan_poison variable in free_pages_prepare" Date: Tue, 28 Mar 2023 16:42:48 +0200 Message-Id: <20230328142628.223011878@linuxfoundation.org> X-Mailer: git-send-email 2.40.0 In-Reply-To: <20230328142619.643313678@linuxfoundation.org> References: <20230328142619.643313678@linuxfoundation.org> User-Agent: quilt/0.67 Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Peter Collingbourne 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@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 Reviewed-by: Andrey Konovalov Cc: Andrey Ryabinin Cc: Catalin Marinas [arm64] Cc: Evgenii Stepanov Cc: Vincenzo Frascino Cc: Will Deacon Cc: [6.1] Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- mm/page_alloc.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1391,6 +1391,7 @@ 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); @@ -1463,7 +1464,7 @@ 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. */