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[70.27.3.10]) by smtp.gmail.com with ESMTPSA id t8-20020a92cc48000000b002e157453a74sm2813487ilq.28.2022.08.11.06.59.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 11 Aug 2022 06:59:28 -0700 (PDT) Date: Thu, 11 Aug 2022 09:59:27 -0400 From: Peter Xu To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org Subject: Re: [PATCH v2 2/2] mm/hugetlb: support write-faults in shared mappings Message-ID: References: <20220811103435.188481-1-david@redhat.com> <20220811103435.188481-3-david@redhat.com> MIME-Version: 1.0 In-Reply-To: <20220811103435.188481-3-david@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1660226373; 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: in-reply-to:in-reply-to:references:references:dkim-signature; bh=rYsvZrJERSFCTDNNMPCNpBJ2PLMPF48eso2jkLERrqI=; b=PJe4foD7vIjygrLqHf9mtYobvJVNBSCwo+IfrPazce/n/BA7BNRVDxLEHDxytTjRdGPtEl jkk9c4OWNcVOczYCzRnbnwalvbqOj+gnROYuuBWE0z3dGy1mvVR2jnSP7Wt8lG7bBsP6h3 kUnnlhHB9gtuXO1aZAOSq6lqbtcCiCc= ARC-Authentication-Results: i=1; imf03.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=WB6ihcyr; spf=pass (imf03.hostedemail.com: domain of peterx@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=peterx@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1660226373; a=rsa-sha256; cv=none; b=j97M3Ntd0ewUNwnmc3tdarHubXOSf7T7ddt183xH/9V/LUvYkYcbchH25IlRdFFk0vkrzd bJrbX4bPg+mXh3/C0F62y20iohyI0j6wMh2LGiK+QJlLR245P6ulh5LqK1Q84QadIBo21a KFEPo0ooows1n8EN0f+sLAQjEqesVcE= X-Stat-Signature: zadc64wf959wwispi1dzeep946dqbwbr X-Rspamd-Queue-Id: 39B5A20030 Authentication-Results: imf03.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=WB6ihcyr; spf=pass (imf03.hostedemail.com: domain of peterx@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=peterx@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1660226371-864100 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, Aug 11, 2022 at 12:34:35PM +0200, David Hildenbrand wrote: > Reason is that uffd-wp doesn't clear the uffd-wp PTE bit when > unregistering and consequently keeps the PTE writeprotected. Reason for > this is to avoid the additional overhead when unregistering. Note > that this is the case also for !hugetlb and that we will end up with > writable PTEs that still have the uffd-wp PTE bit set once we return > from hugetlb_wp(). I'm not touching the uffd-wp PTE bit for now, because it > seems to be a generic thing -- wp_page_reuse() also doesn't clear it. This may justify that lazy reset of ptes may not really be a good idea, including anonymous. I'm indeed not aware of any app that do frequent reg/unreg at least. I'll prepare a patch to change it from uffd side too. Thanks again for finding this problem. -- Peter Xu