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identity=mailfrom; envelope-from=""; helo=NAM02-DM3-obe.outbound.protection.outlook.com; client-ip=40.107.95.65 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1616508289-187449 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 Tue, Mar 23, 2021 at 12:47:24PM +0100, Daniel Vetter wrote: > > +static inline bool is_cow_mapping(vm_flags_t flags) > > Bit a bikeshed, but I wonder whether the public interface shouldn't be > vma_is_cow_mapping. Or whether this shouldn't be rejected somewhere else, > since at least in drivers/gpu we have tons of cases that don't check for > this and get it all kinds of wrong I think. > > remap_pfn_range handles this for many cases, but by far not for all. > > Anyway patch itself lgtm: > > Reviewed-by: Daniel Vetter I would like it if io_remap_pfn_range() did not allow shared mappings at all. IIRC it doesn't work anyway, the kernel can't reliably copy from IO pages eg the "_copy_from_user_inatomic()" under cow_user_page() will not work on s390 that requires all IO memory be accessed with special instructions. Unfortunately I have no idea what the long ago special case of allowing COW'd IO mappings is. :\ Jason