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[184.147.118.108]) by smtp.gmail.com with ESMTPSA id y1sm4320510qkp.21.2021.06.04.08.10.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 04 Jun 2021 08:10:32 -0700 (PDT) Date: Fri, 4 Jun 2021 11:10:31 -0400 From: Peter Xu To: Hugh Dickins Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Andrea Arcangeli Subject: Re: [PATCH] mm/swap: Fix pte_same_as_swp() not removing uffd-wp bit when compare Message-ID: References: <20210603180546.9083-1-peterx@redhat.com> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: EF6F020021C5 X-Stat-Signature: kqcrdzahyiftpehzfu84kaa4xm5kees9 Authentication-Results: imf11.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=NkNGqVuO; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf11.hostedemail.com: domain of peterx@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=peterx@redhat.com X-HE-Tag: 1622819417-339749 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 Thu, Jun 03, 2021 at 08:26:02PM -0700, Hugh Dickins wrote: > On Thu, 3 Jun 2021, Peter Xu wrote: > > > I found it by pure code review, that pte_same_as_swp() of unuse_vma() didn't > > Yes, that is an odd corner, easily missed. > > > take uffd-wp bit into account when comparing ptes. pte_same_as_swp() returning > > false negative could cause failure to swapoff swap ptes that was wr-protected > > by userfaultfd. > > > > Cc: Hugh Dickins > > Cc: Andrea Arcangeli > > Cc: Andrew Morton > > Signed-off-by: Peter Xu > > I expect you're right: swapoff used to hang forever (but interruptibly) > when this went wrong on powerpc originally. I don't know the uffd_wp > (nor the soft_dirty) end of it, but treating uffd_wp and soft_dirty > together looks a very good approach, so I'll venture an > > Acked-by: Hugh Dickins Thanks! > > But I think it should have a uffd_wp Fixes tag and be Cc stable. Yes, should be: Cc: stable@vger.kernel.org # v5.7+ Fixes: f45ec5ff16a7 ("userfaultfd: wp: support swap and page migration") -- Peter Xu