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[209.132.183.28]) by mx.google.com with ESMTPS id w18si3080625qka.41.2019.02.25.23.54.57 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 25 Feb 2019 23:54:57 -0800 (PST) Received-SPF: pass (google.com: domain of peterx@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of peterx@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=peterx@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id ABD7D3082B21; Tue, 26 Feb 2019 07:54:56 +0000 (UTC) Received: from xz-x1 (dhcp-14-116.nay.redhat.com [10.66.14.116]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 7D2A21001DE2; Tue, 26 Feb 2019 07:54:46 +0000 (UTC) Date: Tue, 26 Feb 2019 15:54:44 +0800 From: Peter Xu To: Mike Rapoport Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, David Hildenbrand , Hugh Dickins , Maya Gokhale , Jerome Glisse , Pavel Emelyanov , Johannes Weiner , Martin Cracauer , Shaohua Li , Marty McFadden , Andrea Arcangeli , Mike Kravetz , Denis Plotnikov , Mike Rapoport , Mel Gorman , "Kirill A . Shutemov" , "Dr . David Alan Gilbert" , Rik van Riel Subject: Re: [PATCH v2 20/26] userfaultfd: wp: support write protection for userfault vma range Message-ID: <20190226075444.GO13653@xz-x1> References: <20190212025632.28946-1-peterx@redhat.com> <20190212025632.28946-21-peterx@redhat.com> <20190225205233.GC10454@rapoport-lnx> <20190226060627.GG13653@xz-x1> <20190226064347.GB5873@rapoport-lnx> <20190226072027.GK13653@xz-x1> <20190226074612.GG5873@rapoport-lnx> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190226074612.GG5873@rapoport-lnx> User-Agent: Mutt/1.10.1 (2018-07-13) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.45]); Tue, 26 Feb 2019 07:54:56 +0000 (UTC) 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, Feb 26, 2019 at 09:46:12AM +0200, Mike Rapoport wrote: [...] > > > > > > +int mwriteprotect_range(struct mm_struct *dst_mm, unsigned long start, > > > > > > + unsigned long len, bool enable_wp, bool *mmap_changing) > > > > > > +{ > > > > > > + struct vm_area_struct *dst_vma; > > > > > > + pgprot_t newprot; > > > > > > + int err; > > > > > > + > > > > > > + /* > > > > > > + * Sanitize the command parameters: > > > > > > + */ > > > > > > + BUG_ON(start & ~PAGE_MASK); > > > > > > + BUG_ON(len & ~PAGE_MASK); > > > > > > + > > > > > > + /* Does the address range wrap, or is the span zero-sized? */ > > > > > > + BUG_ON(start + len <= start); > > > > > > > > > > I'd replace these BUG_ON()s with > > > > > > > > > > if (WARN_ON()) > > > > > return -EINVAL; > > > > > > > > I believe BUG_ON() is used because these parameters should have been > > > > checked in userfaultfd_writeprotect() already by the common > > > > validate_range() even before calling mwriteprotect_range(). So I'm > > > > fine with the WARN_ON() approach but I'd slightly prefer to simply > > > > keep the patch as is to keep Jerome's r-b if you won't disagree. :) > > > > > > Right, userfaultfd_writeprotect() should check these parameters and if it > > > didn't it was a bug indeed. But still, it's not severe enough to crash the > > > kernel. > > > > > > I hope Jerome wouldn't mind to keep his r-b with s/BUG_ON/WARN_ON ;-) > > > > > > With this change you can also add > > > > > > Reviewed-by: Mike Rapoport > > > > Thanks! Though before I change anything... please note that the > > BUG_ON()s are really what we've done in existing MISSING code. One > > example is userfaultfd_copy() which did validate_range() first, then > > in __mcopy_atomic() we've used BUG_ON()s. They make sense to me > > becauase userspace should never be able to trigger it. And if we > > really want to change the BUG_ON()s in this patch, IMHO we probably > > want to change the other BUG_ON()s as well, then that can be a > > standalone patch or patchset to address another issue... > > Yeah, we have quite a lot of them, so doing the replacement in a separate > patch makes perfect sense. > > > (and if we really want to use WARN_ON, I would prefer WARN_ON_ONCE, or > > directly return the errors to avoid DOS). > > Agree. > > > I'll see how you'd prefer to see how I should move on with this patch. > > Let's keep this patch as is and make the replacement on top of the WP > series. Feel free to add r-b. Great! I'll do. Thanks, -- Peter Xu