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Tue, 31 Oct 2023 07:10:10 -0700 (PDT) Date: Tue, 31 Oct 2023 07:10:08 -0700 In-Reply-To: Mime-Version: 1.0 References: <20231027182217.3615211-1-seanjc@google.com> <20231027182217.3615211-17-seanjc@google.com> Message-ID: Subject: Re: [PATCH v13 16/35] KVM: Add KVM_CREATE_GUEST_MEMFD ioctl() for guest-specific backing memory From: Sean Christopherson To: Chao Gao Cc: Paolo Bonzini , Marc Zyngier , Oliver Upton , Huacai Chen , Michael Ellerman , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexander Viro , Christian Brauner , "Matthew Wilcox (Oracle)" , Andrew Morton , kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Xiaoyao Li , Xu Yilun , Chao Peng , Fuad Tabba , Jarkko Sakkinen , Anish Moorthy , David Matlack , Yu Zhang , Isaku Yamahata , "=?utf-8?Q?Micka=C3=ABl_Sala=C3=BCn?=" , Vlastimil Babka , Vishal Annapurve , Ackerley Tng , Maciej Szmigiero , David Hildenbrand , Quentin Perret , Michael Roth , Wang , Liam Merwick , Isaku Yamahata , "Kirill A . Shutemov" Content-Type: text/plain; charset="us-ascii" X-Stat-Signature: 95hfijj8ii47xbwo756fn9h1ypqbjpbc X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 3C691140020 X-Rspam-User: X-HE-Tag: 1698761410-339072 X-HE-Meta: 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 B6IApst2 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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: List-Subscribe: List-Unsubscribe: On Tue, Oct 31, 2023, Chao Gao wrote: > >+int kvm_gmem_create(struct kvm *kvm, struct kvm_create_guest_memfd *args) > >+{ > >+ loff_t size = args->size; > >+ u64 flags = args->flags; > >+ u64 valid_flags = 0; > >+ > >+ if (flags & ~valid_flags) > >+ return -EINVAL; > >+ > >+ if (size < 0 || !PAGE_ALIGNED(size)) > >+ return -EINVAL; > > is size == 0 a valid case? Nope, this is a bug. > >+ if (!xa_empty(&gmem->bindings) && > >+ xa_find(&gmem->bindings, &start, end - 1, XA_PRESENT)) { > >+ filemap_invalidate_unlock(inode->i_mapping); > >+ goto err; > >+ } > >+ > >+ /* > >+ * No synchronize_rcu() needed, any in-flight readers are guaranteed to > >+ * be see either a NULL file or this new file, no need for them to go > >+ * away. > >+ */ > >+ rcu_assign_pointer(slot->gmem.file, file); > >+ slot->gmem.pgoff = start; > >+ > >+ xa_store_range(&gmem->bindings, start, end - 1, slot, GFP_KERNEL); > >+ filemap_invalidate_unlock(inode->i_mapping); > >+ > >+ /* > >+ * Drop the reference to the file, even on success. The file pins KVM, > >+ * not the other way 'round. Active bindings are invalidated if the > >+ * file is closed before memslots are destroyed. > >+ */ > >+ fput(file); > >+ return 0; > >+ > >+err: > >+ fput(file); > >+ return -EINVAL; > > The cleanup, i.e., filemap_invalidate_unlock() and fput(), is common. So, I think it > may be slightly better to consolidate the common part e.g., I would prefer to keep this as-is. Only goto needs the unlock, and I find it easier to understand the success vs. error paths with explicit returns. But it's not a super strong preference.