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a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:x-gm-message-state:from:to:cc :subject:date; bh=KtLw4C6VhVX+NvaGxIgELiy/zqMzxZXxqnnlbY2OKmo=; b=qtPzfN7nvYr2pvkdDLbN/2X9UNrX3Jh/d91/VII1YUkwGRWJKgNiv3LAsT1rflGR4l dE9RlkEWMAHL36vpPJfB1TtHZtHEvWCxKb9VzhaynfmSy43+S4/WMTRDOqO48UyS32Jd PzDw5h4dBFVkiVUhyDgirqGfuwfHDQFMChDtDzifGPE3E8IIOBoeYnZwk5QegGAxCDtQ bueTXBWy6Y2eFz6LW8K2uqBV5U08d7rV9CH5VN4Qjlu+trX8p6bfjbvCBr69tBxfTxf1 0MwzMLRzswCLyTX0WOEE566AWvhvQtEXtLQfFpyTs93c7Cq0R+4VDZcsO9fkqIURgAli ESfQ== X-Gm-Message-State: ACgBeo2JPj5Gd+FUKfR1HVSp27JtWkfZJxIdAif+PJhGCwuoz8wOLHyl qsur3Twyayc16DPo01BMEAAfOHHuduFlD4vGyvtyZA== X-Google-Smtp-Source: AA6agR6FKEIXt4Le+vLLG6frjvQmxHhi7IpkWph1Sqqg5DDpP37KZzCFD7SHe2MzUi799BfLdccL/mK6LPn2rgcWHb8= X-Received: by 2002:a05:6902:2d0:b0:694:d257:4c4b with SMTP id w16-20020a05690202d000b00694d2574c4bmr9751150ybh.316.1662683237776; Thu, 08 Sep 2022 17:27:17 -0700 (PDT) MIME-Version: 1.0 References: <20220901173516.702122-1-surenb@google.com> <20220901173516.702122-10-surenb@google.com> <98d5f462-c4dc-a967-0ab0-f24dd3e37dff@linux.ibm.com> In-Reply-To: <98d5f462-c4dc-a967-0ab0-f24dd3e37dff@linux.ibm.com> From: Suren Baghdasaryan Date: Thu, 8 Sep 2022 17:27:06 -0700 Message-ID: Subject: Re: [RFC PATCH RESEND 09/28] mm/mempolicy: mark VMA as locked when changing protection policy To: Laurent Dufour Cc: akpm@linux-foundation.org, michel@lespinasse.org, jglisse@google.com, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, mgorman@suse.de, dave@stgolabs.net, willy@infradead.org, liam.howlett@oracle.com, peterz@infradead.org, laurent.dufour@fr.ibm.com, paulmck@kernel.org, luto@kernel.org, songliubraving@fb.com, peterx@redhat.com, david@redhat.com, dhowells@redhat.com, hughd@google.com, bigeasy@linutronix.de, kent.overstreet@linux.dev, rientjes@google.com, axelrasmussen@google.com, joelaf@google.com, minchan@google.com, kernel-team@android.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, x86@kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1662683238; a=rsa-sha256; cv=none; b=w2t6BNvjtEkN0yB2+vlNzrZsJqUkPbGViL+jJ/z9n3gr1+9ZCagLm7LXu8+zPOGDhabB0l 7SXJGPxsYvymLCRhSVeUglsXPvBP8mOkSKAoO5DKY7RKcmccQnBdx770WpQeIpQPuVAKX1 GXlLcs/Fv8GpFXnffFdnKGHb3D8Qeiw= ARC-Authentication-Results: i=1; imf13.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=crQ36UMH; spf=pass (imf13.hostedemail.com: domain of surenb@google.com designates 209.85.219.180 as permitted sender) smtp.mailfrom=surenb@google.com; dmarc=pass (policy=reject) header.from=google.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1662683238; 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=KtLw4C6VhVX+NvaGxIgELiy/zqMzxZXxqnnlbY2OKmo=; b=yo+XtWOTYHS288djSGQKwtalB8Ra/PhW3hsIpmcCIOjDwF5B0Bk6lyeIFqXfnkaP36rKMY HcwVkDY7FUunp7ATItNVA8W7X4k8yrJxbcLc3vTVNURrGne6uj9zVGqwi6zaG0hZv5967I WU/I3rwkuWteioQjrVHiBcr47srwZR0= X-Stat-Signature: 9gicxx7qump4xnsq779c41py685dk933 X-Rspam-User: X-Rspamd-Queue-Id: ADD2F20078 X-Rspamd-Server: rspam07 Authentication-Results: imf13.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=crQ36UMH; spf=pass (imf13.hostedemail.com: domain of surenb@google.com designates 209.85.219.180 as permitted sender) smtp.mailfrom=surenb@google.com; dmarc=pass (policy=reject) header.from=google.com X-HE-Tag: 1662683238-556731 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 Tue, Sep 6, 2022 at 7:48 AM Laurent Dufour wrote= : > > Le 01/09/2022 =C3=A0 19:34, Suren Baghdasaryan a =C3=A9crit : > > Protect VMA from concurrent page fault handler while performing VMA > > protection policy changes. > > > > Signed-off-by: Suren Baghdasaryan > > --- > > mm/mempolicy.c | 6 +++++- > > 1 file changed, 5 insertions(+), 1 deletion(-) > > > > diff --git a/mm/mempolicy.c b/mm/mempolicy.c > > index b73d3248d976..6be1e5c75556 100644 > > --- a/mm/mempolicy.c > > +++ b/mm/mempolicy.c > > @@ -383,8 +383,10 @@ void mpol_rebind_mm(struct mm_struct *mm, nodemask= _t *new) > > struct vm_area_struct *vma; > > > > mmap_write_lock(mm); > > - for (vma =3D mm->mmap; vma; vma =3D vma->vm_next) > > + for (vma =3D mm->mmap; vma; vma =3D vma->vm_next) { > > + vma_mark_locked(vma); > > mpol_rebind_policy(vma->vm_policy, new); > > + } > > mmap_write_unlock(mm); > > } > > > > @@ -632,6 +634,7 @@ unsigned long change_prot_numa(struct vm_area_struc= t *vma, > > struct mmu_gather tlb; > > int nr_updated; > > > > + vma_mark_locked(vma); > > If I understand that corretly, the VMA itself is not impacted, only the > PMDs/PTEs, and they are protected using the page table locks. > > Am I missing something? I thought we would not want pages faulting in the VMA for which we are changing the protection. However I think what you are saying is that page table locks would already provide a more granular synchronization with page fault handlers, which makes sense to me. Sounds like we can skip locking the VMA here as well. Nice! > > > tlb_gather_mmu(&tlb, vma->vm_mm); > > > > nr_updated =3D change_protection(&tlb, vma, addr, end, PAGE_NONE, > > @@ -765,6 +768,7 @@ static int vma_replace_policy(struct vm_area_struct= *vma, > > if (IS_ERR(new)) > > return PTR_ERR(new); > > > > + vma_mark_locked(vma); > > if (vma->vm_ops && vma->vm_ops->set_policy) { > > err =3D vma->vm_ops->set_policy(vma, new); > > if (err) >