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[99.254.144.39]) by smtp.gmail.com with ESMTPSA id o11-20020ac872cb000000b004055106ee80sm195044qtp.44.2023.07.28.12.50.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 28 Jul 2023 12:50:30 -0700 (PDT) Date: Fri, 28 Jul 2023 15:50:29 -0400 From: Peter Xu To: David Hildenbrand Cc: Linus Torvalds , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Andrew Morton , liubo , Matthew Wilcox , Hugh Dickins , Jason Gunthorpe , John Hubbard , Mel Gorman Subject: Re: [PATCH v1 0/4] smaps / mm/gup: fix gup_can_follow_protnone fallout Message-ID: References: <20230727212845.135673-1-david@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-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 9B22EC000D X-Stat-Signature: 7abks9xn9y5nuq8h6668gjm18r7yh1z9 X-HE-Tag: 1690573834-817655 X-HE-Meta: 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 5ThPGkNO DoVtkV080eAxw2aLMVcbDRKG+YTkx7WwjmQ/sDhf93yOzM/bjC1xH0b+A8+SoiloU7Q/SBkAFUnk9Z4tl7rsCPCor7UpyIePBHeIIbQvbjQhIYtJz/iJgtl4LlfbVJAxf3gd0oCUDULY8TcUU1upUIimUsj5u3pfDwjL+4W/R8ni8fcss+369wjmGreaTKBADNVA/2HRdkWYuHi8atvnkj7kW4RgXRs0Fo8FAGGiuDlaklYlsciyMp6jW94Q+DGKyJurAcTsNyLDFRERORC8Q2lmKyhJuwXzpuGlVzcLnLXcN8rofZ7P4ukz14zz42Ota25zS6JKhPAgVwZhFa/nNeObPsdFFOppgvVyLy+W+i7OQV7uTnCEdkUubu8xKPLOqex/EjsmTGrhHJzin6u7V8tr8wR0lFoTy2mTo 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 Fri, Jul 28, 2023 at 09:40:54PM +0200, David Hildenbrand wrote: > Hmm. So three alternatives I see: > > 1) Use FOLL_FORCE in follow_page() to unconditionally disable protnone > checks. Alternatively, have an internal FOLL_NO_PROTNONE flag if we > don't like that. > > 2) Revert the commit and reintroduce unconditional FOLL_NUMA without > FOLL_FORCE. > > 3) Have a FOLL_NUMA that callers like KVM can pass. I'm afraid 3) means changing numa balancing to opt-in, probably no-go for any non-kvm gup users as that could start to break there, even if making smaps/follow_page happy again. I keep worrying 1) on FOLL_FORCE abuse. So I keep my vote on 2). Thanks, -- Peter Xu