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 iXToD+tp cpmRDCDuvEHw7FLlUfjh6f6n7wGXv+VcQNSka2ddNDkvKOnHWGozc6m4ghrPSlwt9XREv2HBpEh1m78oADfUQ2id0CPQGFawhxZpjUmj3JCLLN9VdO3LzaFrk7NTeZo+XdCQ+ 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, Sep 16, 2025 at 02:40:06PM -0300, Jason Gunthorpe wrote: > On Tue, Sep 16, 2025 at 03:11:57PM +0100, Lorenzo Stoakes wrote: > > Update the mem char driver (backing /dev/mem and /dev/zero) to use > > f_op->mmap_prepare hook rather than the deprecated f_op->mmap. > > > > The /dev/zero implementation has a very unique and rather concerning > > characteristic in that it converts MAP_PRIVATE mmap() mappings anonymous > > when they are, in fact, not. > > > > The new f_op->mmap_prepare() can support this, but rather than introducing > > a helper function to perform this hack (and risk introducing other users), > > simply set desc->vm_op to NULL here and add a comment describing what's > > going on. > > > > We also introduce shmem_zero_setup_desc() to allow for the shared mapping > > case via an f_op->mmap_prepare() hook, and generalise the code between > > this and shmem_zero_setup(). > > > > We also use the desc->action_error_hook to filter the remap error to > > -EAGAIN to keep behaviour consistent. > > Hurm, in practice this converts reserve_pfn_range()/etc conflicts into > from EINVAL into EAGAIN and converts all the unlikely OOM ENOMEM > failures to EAGAIN. Seems wrong/unnecessary to me, I wouldn't have > preserved it. Yeah I don't love it, people get antsy sometimes about changing what the error code is. I'd rather pass through than filter but there we are. > > But oh well > > Reviewed-by: Jason Gunthorpe Thanks! > > > diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h > > index 0e47465ef0fd..5b368f9549d6 100644 > > --- a/include/linux/shmem_fs.h > > +++ b/include/linux/shmem_fs.h > > This little bit should probably be its own patch "Add > shmem_zero_setup_desc()", and I wonder if the caller from vma.c can > call the desc version now? Ack! Let me look into whether vma.c caller can use that also. > > Too bad the usage in ppc is such an adventure through sysfs :\ The arch code sure can be fun! > > But the code looks fine Cheers! > > Jason Cheers, Lorenzo