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Gleixner , linux-alpha@vger.kernel.org, Yury Norov , linux-kernel@vger.kernel.org, linux-snps-arc@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, kvm@vger.kernel.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, linux-um@lists.infradead.org, dmaengine@vger.kernel.org, linux-efi@vger.kernel.org, linux-fsi@lists.ozlabs.org, amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, linux-wpan@vger.kernel.org, netdev@vger.kernel.org, linux-wireless@vger.kernel.org, linux-spi@vger.kernel.org, linux-media@vger.kernel.org, linux-staging@lists.linux.dev, linux-serial@vger.kernel.org, linux-usb@vger.kernel.org, xen-devel@lists.xenproject.org, linux-fsdevel@vger.kernel.org, ocfs2-devel@lists.linux.dev, bpf@vger.kernel.org, kasan-dev@googlegroups.com, linux-mm@kvack.org, linux-x25@vger.kernel.org, rust-for-linux@vger.kernel.org, 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At the time being, x86 and arm64 are missing unsafe_copy_from_user(). > > > > No, they don't. They (should) rely on a generic implementation from > > linux/uaccess.h, like every other arch, except for PPC and RISCV. > > > > But they #define arch_unsafe_get_user, and the unsafe_copy_from_user() > > becomes undefined conditionally on that. > > > > So please, fix that bug instead of introducing another arch flavor. > > We'd always choose generic version, unless there's strong evidence > > that arch one is better. > > But they both implement the exact same unsafe_copy_to_user(). What is the > difference here ? > > Should that function become generic too ? This is what Linus said when added x86 implementation for copy_from_user() in c512c69187197: Note that it only does this [arch version] for the copying _to_ user space, and we still don't have a unsafe version of copy_from_user(). That's partly because we have no current users of it, but also partly because the copy_from_user() case is slightly different and cannot efficiently be implemented in terms of a unsafe_get_user() loop (because gcc can't do asm goto with outputs). In the unsafe_copy_to_user case, arch versions were justified. Just as said, I'm not against arch version for unsafe_copy_from_user(), but it should be explained very well.