From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 9667316EB42 for ; Wed, 30 Apr 2025 05:44:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745991873; cv=none; b=b9B3H2nQTqXFBzLGLOz19aZIb9G0onWSBbH7HoI09giCIbgRjoO2vT93ASFj1hGj7BEeZqcjUwl59+ii7hh5jPHXhGL4iPsxXs8JEnVWHtWJwfC4cgXz6T4vPAxA/DWeZeqvAONC+zPCJGhJ4cD6xj1RO2qqD8RqSmJLcVQJIhM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745991873; c=relaxed/simple; bh=X2wAr44kyEa1wXomBZkP0S30pU+20A2JzbIbMT1DTAY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=T5CKq0HHwrrqleQsPjjoIYk8vDRbx2747ld4lJhr4jYcheOrOGpX5AeiWGfvwGrIa8jyRr2w53voYs+Ueyv0pLDVdQfvLlcctRUo0SklinrHYqR6xePi0SqWOwAP7RLMg0LUGD2TKhqa7QfORmLJCJmQywLfXt0jX7I3lqMVPi4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A4F4D106F; Tue, 29 Apr 2025 22:44:23 -0700 (PDT) Received: from [10.163.79.251] (unknown [10.163.79.251]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 4FC553F5A1; Tue, 29 Apr 2025 22:44:22 -0700 (PDT) Message-ID: Date: Wed, 30 Apr 2025 11:14:18 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 6/7] mm: Batch around can_change_pte_writable() To: Lorenzo Stoakes , David Hildenbrand Cc: akpm@linux-foundation.org, ryan.roberts@arm.com, willy@infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, catalin.marinas@arm.com, will@kernel.org, Liam.Howlett@oracle.com, vbabka@suse.cz, jannh@google.com, anshuman.khandual@arm.com, peterx@redhat.com, joey.gouly@arm.com, ioworker0@gmail.com, baohua@kernel.org, kevin.brodsky@arm.com, quic_zhenhuah@quicinc.com, christophe.leroy@csgroup.eu, yangyicong@hisilicon.com, linux-arm-kernel@lists.infradead.org, hughd@google.com, yang@os.amperecomputing.com, ziy@nvidia.com References: <20250429052336.18912-1-dev.jain@arm.com> <20250429052336.18912-7-dev.jain@arm.com> <25dcf969-e479-4d4a-a95c-0e83706af99e@redhat.com> <9a770aec-a020-4199-a53e-eddda657999d@redhat.com> <7cf8235e-21f7-4643-82c4-82ad57d99b98@lucifer.local> Content-Language: en-US From: Dev Jain In-Reply-To: <7cf8235e-21f7-4643-82c4-82ad57d99b98@lucifer.local> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 29/04/25 7:27 pm, Lorenzo Stoakes wrote: > On Tue, Apr 29, 2025 at 11:27:43AM +0200, David Hildenbrand wrote: >> On 29.04.25 11:19, David Hildenbrand wrote: >>> >>>> #include "internal.h" >>>> -bool can_change_pte_writable(struct vm_area_struct *vma, unsigned long addr, >>>> - pte_t pte) >>>> +bool can_change_ptes_writable(struct vm_area_struct *vma, unsigned long addr, >>>> + pte_t pte, struct folio *folio, unsigned int nr) >>>> { >>>> struct page *page; >>>> @@ -67,8 +67,9 @@ bool can_change_pte_writable(struct vm_area_struct *vma, unsigned long addr, >>>> * write-fault handler similarly would map them writable without >>>> * any additional checks while holding the PT lock. >>>> */ >>>> - page = vm_normal_page(vma, addr, pte); >>>> - return page && PageAnon(page) && PageAnonExclusive(page); >>>> + if (!folio) >>>> + folio = vm_normal_folio(vma, addr, pte); >>>> + return folio_test_anon(folio) && !folio_maybe_mapped_shared(folio); >>> >>> Oh no, now I spot it. That is horribly wrong. >>> >>> Please understand first what you are doing. >> >> Also, would expect that the cow.c selftest would catch that: >> >> "vmsplice() + unmap in child with mprotect() optimization" >> >> After fork() we have a R/O PTE in the parent. Our child then uses vmsplice() >> and unmaps the R/O PTE, meaning it is only left mapped by the parent. >> >> ret = mprotect(mem, size, PROT_READ); >> ret |= mprotect(mem, size, PROT_READ|PROT_WRITE); >> >> should turn the PTE writable, although it shouldn't. > > This makes me concerned about the stability of this series as a whole... > >> >> If that test case does not detect the issue you're introducing, we should >> look into adding a test case that detects it. > > There are 25 tests that fail for the cow self-test with this series > applied: > > # [RUN] vmsplice() + unmap in child with mprotect() optimization ... with base page > # [RUN] vmsplice() + unmap in child with mprotect() optimization ... with PTE-mapped THP (16 kB) > # [RUN] vmsplice() + unmap in child with mprotect() optimization ... with single PTE of THP (16 kB) > # [RUN] vmsplice() + unmap in child with mprotect() optimization ... with partially shared THP (16 kB) > # [RUN] vmsplice() + unmap in child with mprotect() optimization ... with PTE-mapped THP (32 kB) > # [RUN] vmsplice() + unmap in child with mprotect() optimization ... with single PTE of THP (32 kB) > # [RUN] vmsplice() + unmap in child with mprotect() optimization ... with partially shared THP (32 kB) > # [RUN] vmsplice() + unmap in child with mprotect() optimization ... with PTE-mapped THP (64 kB) > # [RUN] vmsplice() + unmap in child with mprotect() optimization ... with single PTE of THP (64 kB) > # [RUN] vmsplice() + unmap in child with mprotect() optimization ... with partially shared THP (64 kB) > # [RUN] vmsplice() + unmap in child with mprotect() optimization ... with PTE-mapped THP (128 kB) > # [RUN] vmsplice() + unmap in child with mprotect() optimization ... with single PTE of THP (128 kB) > # [RUN] vmsplice() + unmap in child with mprotect() optimization ... with partially shared THP (128 kB) > # [RUN] vmsplice() + unmap in child with mprotect() optimization ... with PTE-mapped THP (256 kB) > # [RUN] vmsplice() + unmap in child with mprotect() optimization ... with single PTE of THP (256 kB) > # [RUN] vmsplice() + unmap in child with mprotect() optimization ... with partially shared THP (256 kB) > # [RUN] vmsplice() + unmap in child with mprotect() optimization ... with PTE-mapped THP (512 kB) > # [RUN] vmsplice() + unmap in child with mprotect() optimization ... with single PTE of THP (512 kB) > # [RUN] vmsplice() + unmap in child with mprotect() optimization ... with partially shared THP (512 kB) > # [RUN] vmsplice() + unmap in child with mprotect() optimization ... with PTE-mapped THP (1024 kB) > # [RUN] vmsplice() + unmap in child with mprotect() optimization ... with single PTE of THP (1024 kB) > # [RUN] vmsplice() + unmap in child with mprotect() optimization ... with partially shared THP (1024 kB) > # [RUN] vmsplice() + unmap in child with mprotect() optimization ... with PTE-mapped THP (2048 kB) > # [RUN] vmsplice() + unmap in child with mprotect() optimization ... with single PTE of THP (2048 kB) > # [RUN] vmsplice() + unmap in child with mprotect() optimization ... with partially shared THP (2048 kB) > > > Dev, please take a little more time to test your series :) the current > patch set doesn't compile and needs fixes applied to do so, and we're at > v2, and you've clearly not run self-tests as these also fail. > > Please ensure you do a smoke test and check compilation before sending out, > as well as running self tests also. Apologies, I over-confidently skipped over selftests, and didn't build for x86 :( Shall take care. > > Thanks, Lorenzo > >> >> -- >> Cheers, >> >> David / dhildenb >>