From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from madrid.collaboradmins.com (madrid.collaboradmins.com [46.235.227.194]) (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 2BE3A56768; Mon, 29 Apr 2024 13:27:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=46.235.227.194 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1714397276; cv=none; b=Fjd6+4FczwdbuP0piPczTrTyMjFRaIjOSxOmLk38h6jrexHcQWXW8iGVALnOoFZHrvGG+7FjvrM4SsmHguRTylYs+9xI8uL9SeIEsZe5dQmTPISS0qwGi2wOv/xwrhhSLqIatiJ7RACOO/pKt5wcJTsnec2iMtNaYjBsigC1c/c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1714397276; c=relaxed/simple; bh=uu+beZKI3o95LC0DBDGmU+b7eBp2cD9rZyXroXh6L0Y=; h=Message-ID:Date:MIME-Version:Cc:Subject:To:References:From: In-Reply-To:Content-Type; b=owqfQiOddXpaxg/gPycMKQANUJP7H59UdIMJ3m/AIUi80BegGvUJ71E0ViJBYPz0huBe/1lOLdfCGya5v6C9ii878coQh4OBZWPPaXKvuPtmPT7tY0DJVO7IZmIAaDhPrAo1hCMaISXFr3SefYQO56oyOo4SLF7mK3mS94bUYUE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=collabora.com; spf=pass smtp.mailfrom=collabora.com; dkim=pass (2048-bit key) header.d=collabora.com header.i=@collabora.com header.b=Gjh+jVlS; arc=none smtp.client-ip=46.235.227.194 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=collabora.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=collabora.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=collabora.com header.i=@collabora.com header.b="Gjh+jVlS" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1714397273; bh=uu+beZKI3o95LC0DBDGmU+b7eBp2cD9rZyXroXh6L0Y=; h=Date:Cc:Subject:To:References:From:In-Reply-To:From; b=Gjh+jVlSPSai+JANWfpL6b2N4ly11fetxM6hx+ZDtsVQn+yrw8y7tDYNDvvSJ7nkf PcTe/2BBdENnU8q4wsJS8VpIaOs2AVGiUEgZGp/qr1pjqqDCNljRYYRR3nxOHRvmQJ QlqwiLxJgd4RfYjnrwandAcui3TlV4gjhaMk/Lghva32zDQt6TAg3IYjJAGpVzcnQs FPuTxUgC2o1NQLYp3o0zeSlo1fIq/thKXduGYYLjrf4+pXpPwR9YWRfcWlIaZW5ztY eCLm/Rs/dTFCa3mjMf2Rrr2RR0hRZylvmSmMAQfugxw3o7eIiNCoQ/hMqaiDgMvg5D ecyr7i8gzrCEQ== Received: from [10.193.1.1] (broslavsky.collaboradmins.com [68.183.210.73]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: usama.anjum) by madrid.collaboradmins.com (Postfix) with ESMTPSA id 2F3C53780C22; Mon, 29 Apr 2024 13:27:50 +0000 (UTC) Message-ID: <256aa75f-abaa-45b5-8615-537e50a5077a@collabora.com> Date: Mon, 29 Apr 2024 18:28:20 +0500 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Cc: Muhammad Usama Anjum , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH v1] fs/proc/task_mmu: Fix uffd-wp confusion in pagemap_scan_pmd_entry() To: Ryan Roberts , Andrew Morton , David Hildenbrand , Peter Xu References: <20240429114104.182890-1-ryan.roberts@arm.com> Content-Language: en-US From: Muhammad Usama Anjum In-Reply-To: <20240429114104.182890-1-ryan.roberts@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Thanks for finding and fixing Ryan! On 4/29/24 4:41 PM, Ryan Roberts wrote: > pagemap_scan_pmd_entry() checks if uffd-wp is set on each pte to avoid > unnecessary if set. However it was previously checking with > `pte_uffd_wp(ptep_get(pte))` without first confirming that the pte was > present. It is only valid to call pte_uffd_wp() for present ptes. For > swap ptes, pte_swp_uffd_wp() must be called because the uffd-wp bit may > be kept in a different position, depending on the arch. > > This was leading to test failures in the pagemap_ioctl mm selftest, when > bringing up uffd-wp support on arm64 due to incorrectly interpretting > the uffd-wp status of migration entries. > > Let's fix this by using the correct check based on pte_present(). While > we are at it, let's pass the pte to make_uffd_wp_pte() to avoid the > pointless extra ptep_get() which can't be optimized out due to > READ_ONCE() on many arches. > > Closes: https://lore.kernel.org/linux-arm-kernel/ZiuyGXt0XWwRgFh9@x1n/ > Fixes: 12f6b01a0bcb ("fs/proc/task_mmu: add fast paths to get/clear PAGE_IS_WRITTEN flag") > Signed-off-by: Ryan Roberts Reviewed-by: Muhammad Usama Anjum Tested-by: Muhammad Usama Anjum > --- > fs/proc/task_mmu.c | 22 +++++++++++++--------- > 1 file changed, 13 insertions(+), 9 deletions(-) > > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c > index af4bc1da0c01..102f48668c35 100644 > --- a/fs/proc/task_mmu.c > +++ b/fs/proc/task_mmu.c > @@ -1817,10 +1817,8 @@ static unsigned long pagemap_page_category(struct pagemap_scan_private *p, > } > > static void make_uffd_wp_pte(struct vm_area_struct *vma, > - unsigned long addr, pte_t *pte) > + unsigned long addr, pte_t *pte, pte_t ptent) > { > - pte_t ptent = ptep_get(pte); > - > if (pte_present(ptent)) { > pte_t old_pte; > > @@ -2175,9 +2173,12 @@ static int pagemap_scan_pmd_entry(pmd_t *pmd, unsigned long start, > if ((p->arg.flags & PM_SCAN_WP_MATCHING) && !p->vec_out) { > /* Fast path for performing exclusive WP */ > for (addr = start; addr != end; pte++, addr += PAGE_SIZE) { > - if (pte_uffd_wp(ptep_get(pte))) > + pte_t ptent = ptep_get(pte); > + > + if ((pte_present(ptent) && pte_uffd_wp(ptent)) || > + pte_swp_uffd_wp_any(ptent)) > continue; > - make_uffd_wp_pte(vma, addr, pte); > + make_uffd_wp_pte(vma, addr, pte, ptent); > if (!flush_end) > start = addr; > flush_end = addr + PAGE_SIZE; > @@ -2190,8 +2191,10 @@ static int pagemap_scan_pmd_entry(pmd_t *pmd, unsigned long start, > p->arg.return_mask == PAGE_IS_WRITTEN) { > for (addr = start; addr < end; pte++, addr += PAGE_SIZE) { > unsigned long next = addr + PAGE_SIZE; > + pte_t ptent = ptep_get(pte); > > - if (pte_uffd_wp(ptep_get(pte))) > + if ((pte_present(ptent) && pte_uffd_wp(ptent)) || > + pte_swp_uffd_wp_any(ptent)) > continue; > ret = pagemap_scan_output(p->cur_vma_category | PAGE_IS_WRITTEN, > p, addr, &next); > @@ -2199,7 +2202,7 @@ static int pagemap_scan_pmd_entry(pmd_t *pmd, unsigned long start, > break; > if (~p->arg.flags & PM_SCAN_WP_MATCHING) > continue; > - make_uffd_wp_pte(vma, addr, pte); > + make_uffd_wp_pte(vma, addr, pte, ptent); > if (!flush_end) > start = addr; > flush_end = next; > @@ -2208,8 +2211,9 @@ static int pagemap_scan_pmd_entry(pmd_t *pmd, unsigned long start, > } > > for (addr = start; addr != end; pte++, addr += PAGE_SIZE) { > + pte_t ptent = ptep_get(pte); > unsigned long categories = p->cur_vma_category | > - pagemap_page_category(p, vma, addr, ptep_get(pte)); > + pagemap_page_category(p, vma, addr, ptent); > unsigned long next = addr + PAGE_SIZE; > > if (!pagemap_scan_is_interesting_page(categories, p)) > @@ -2224,7 +2228,7 @@ static int pagemap_scan_pmd_entry(pmd_t *pmd, unsigned long start, > if (~categories & PAGE_IS_WRITTEN) > continue; > > - make_uffd_wp_pte(vma, addr, pte); > + make_uffd_wp_pte(vma, addr, pte, ptent); > if (!flush_end) > start = addr; > flush_end = next; > -- > 2.25.1 > -- BR, Muhammad Usama Anjum