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[2003:cb:c704:8c00:eee4:63f0:cef2:5ac0]) by smtp.gmail.com with ESMTPSA id q12-20020adff50c000000b0021e5757fb4csm11192877wro.88.2022.07.25.07.11.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 25 Jul 2022 07:11:20 -0700 (PDT) Message-ID: <1b574e20-26f3-fb3e-69d2-21f35c9e4730@redhat.com> Date: Mon, 25 Jul 2022 16:11:19 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [PATCH v3 1/3] mm/mprotect: Fix soft-dirty check in can_change_pte_writable() To: Peter Xu , Nadav Amit Cc: LKML , Linux MM , Andrew Morton , Andrea Arcangeli References: <20220721183338.27871-1-peterx@redhat.com> <20220721183338.27871-2-peterx@redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1658758284; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=/iwb85TjmRaVZHGqzyek+VGRdYMNOqw3oLLy+2G9Arc=; b=SBTAwhHorhrMH2101ad1uZ6ORy12C1k9Pt3AVRSAPNhqAU1+v5ld4cteNExg8MMLfpJwqP UHGprwDQHqyLJXir2zymwb4FcZ1gT7xsnRed/Bxk102ZekW+m9wsMpAyp6jzxyBPJDdzGu vX5PgGncZAXbPRVSGIsd9LCb+MZZGEQ= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1658758284; a=rsa-sha256; cv=none; b=2iiNatWPISBqoKz8vDGwg0KDtxXsaKdyYamcTorHhs5n+NMBaarSrsqxIGLMrDBtCet7av x26VsHX5m5m42VWfFiXmglBGvmNKVvYkIYNQzzFl3o2FMh/NKrElTsd2PHPVfsEeStlkzI EPWK6ms9uIeZBZCA2km8lqWL2QtSAoQ= ARC-Authentication-Results: i=1; imf18.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=i1Im8tq5; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf18.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=david@redhat.com Authentication-Results: imf18.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=i1Im8tq5; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf18.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=david@redhat.com X-Stat-Signature: dgqia3qnpd386wgk44mseoiso8xi4qfu X-Rspamd-Queue-Id: CAD921C00AC X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1658758284-788543 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 25.07.22 15:59, Peter Xu wrote: > On Fri, Jul 22, 2022 at 10:21:00AM -0700, Nadav Amit wrote: >> On Jul 22, 2022, at 12:08 AM, David Hildenbrand wrote: >> >>>> +static inline bool vma_soft_dirty_enabled(struct vm_area_struct *vma) >>>> +{ >>>> + /* >>>> + * NOTE: we must check this before VM_SOFTDIRTY on soft-dirty >>>> + * enablements, because when without soft-dirty being compiled in, >>>> + * VM_SOFTDIRTY is defined as 0x0, then !(vm_flags & VM_SOFTDIRTY) >>>> + * will be constantly true. >>>> + */ >>>> + if (!IS_ENABLED(CONFIG_MEM_SOFT_DIRTY)) >>>> + return false; >>>> + >>>> + /* >>>> + * Soft-dirty is kind of special: its tracking is enabled when the >>>> + * vma flags not set. >>>> + */ >>>> + return !(vma->vm_flags & VM_SOFTDIRTY); >>>> +} >>> >>> That will come in handy in other patches I'm cooking. >> >> clear_refs_write() also comes to mind as well (for consistency; I see no >> correctness or performance issue). > > I explicitly didn't touch that because current code is better.. > > mas_for_each(&mas, vma, ULONG_MAX) { > if (!(vma->vm_flags & VM_SOFTDIRTY)) > continue; > vma->vm_flags &= ~VM_SOFTDIRTY; > vma_set_page_prot(vma); > } > > It means when !CONFIG_MEM_SOFT_DIRTY the "if" will always be true and all > vma will be jumped. > > If replaced with vma_soft_dirty_enabled() it'll be instead constantly false > returned. We'll redo vma_set_page_prot() even if unnecessary. > > Here if we want to add the "CONFIG_MEM_SOFT_DIRTY" into equation it can be: > > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c > index f8cd58846a28..ab6f2913b5a5 100644 > --- a/fs/proc/task_mmu.c > +++ b/fs/proc/task_mmu.c > @@ -1290,6 +1290,8 @@ static ssize_t clear_refs_write(struct file *file, const char __user *buf, > } > > if (type == CLEAR_REFS_SOFT_DIRTY) { > + if (!IS_ENABLED(CONFIG_MEM_SOFT_DIRTY)) > + goto out_unlock; > mas_for_each(&mas, vma, ULONG_MAX) { > if (!(vma->vm_flags & VM_SOFTDIRTY)) > continue; > > Or even at the entrance to not take the mm sem. But it's not anything > important IMHO, so if no one asking for that I'll just leave it be. Yeah, I don't think we particularly care about that. -- Thanks, David / dhildenb