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Tue, 05 Sep 2023 16:56:32 -0700 (PDT) Date: Tue, 5 Sep 2023 16:56:31 -0700 In-Reply-To: <20230901082025.20548-2-vbabka@suse.cz> Mime-Version: 1.0 References: <20230901082025.20548-2-vbabka@suse.cz> Message-ID: Subject: Re: [PATCH gmem FIXUP] mm, compaction: make testing mapping_unmovable() safe From: Sean Christopherson To: Vlastimil Babka Cc: ackerleytng@google.com, akpm@linux-foundation.org, anup@brainfault.org, aou@eecs.berkeley.edu, chao.p.peng@linux.intel.com, chenhuacai@kernel.org, david@redhat.com, isaku.yamahata@gmail.com, jarkko@kernel.org, jmorris@namei.org, kirill.shutemov@linux.intel.com, kvm-riscv@lists.infradead.org, kvm@vger.kernel.org, kvmarm@lists.linux.dev, liam.merwick@oracle.com, linux-arm-kernel@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org, linux-mm@kvack.org, linux-riscv@lists.infradead.org, linux-security-module@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, mail@maciej.szmigiero.name, maz@kernel.org, michael.roth@amd.com, mpe@ellerman.id.au, oliver.upton@linux.dev, palmer@dabbelt.com, paul.walmsley@sifive.com, paul@paul-moore.com, pbonzini@redhat.com, qperret@google.com, serge@hallyn.com, tabba@google.com, vannapurve@google.com, wei.w.wang@intel.com, willy@infradead.org, yu.c.zhang@linux.intel.com Content-Type: text/plain; charset="us-ascii" X-Rspamd-Queue-Id: CB992C0016 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: wqahmytujuzkmtmzdnw6eghpewzt6153 X-HE-Tag: 1693958193-616834 X-HE-Meta: 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 iy8+HCNp 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 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, Sep 01, 2023, Vlastimil Babka wrote: > As Kirill pointed out, mapping can be removed under us due to > truncation. Test it under folio lock as already done for the async > compaction / dirty folio case. To prevent locking every folio with > mapping to do the test, do it only for unevictable folios, as we can > expect the unmovable mapping folios are also unevictable - it is the > case for guest memfd folios. Rather than expect/assume that unmovable mappings are always unevictable, how about requiring that? E.g. either through a VM_WARN_ON in mapping_set_unmovable(), or by simply having that helper forcefully set AS_UNEVICTABLE as well.