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Date: Tue, 9 Aug 2022 10:32:27 +0200 From: Arnd Bergmann <arnd@...db.de> To: Christoph Hellwig <hch@...radead.org> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Jason Gunthorpe <jgg@...dia.com>, Oded Gabbay <oded.gabbay@...il.com>, Dave Airlie <airlied@...il.com>, dri-devel <dri-devel@...ts.freedesktop.org>, Yuji Ishikawa <yuji2.ishikawa@...hiba.co.jp>, Jiho Chu <jiho.chu@...sung.com>, Arnd Bergmann <arnd@...db.de>, "Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org> Subject: Re: New subsystem for acceleration devices On Tue, Aug 9, 2022 at 10:04 AM Christoph Hellwig <hch@...radead.org> wrote: > On Tue, Aug 09, 2022 at 08:23:27AM +0200, Greg Kroah-Hartman wrote: > > > This is different from the number of FDs pointing at the struct file. > > > Userpsace can open a HW state and point a lot of FDs at it, that is > > > userspace's problem. From a kernel view they all share one struct file > > > and thus one HW state. > > > > Yes, that's fine, if that is what is happening here, I have no > > objection. > > It would be great if we could actually life that into a common > layer (chardev or vfs) given just how common this, and drivers tend > to get it wrong, do it suboptimal so often. Totally agreed. I think for devices with hardware MMU contexts you actually want to bind the context to a 'mm_struct', and then ensure that the context is only ever used from a process that shares this mm_struct, regardless of who else has access to the same file or inode. We did this in a somewhat hacky way in spufs a long time ago, and I would expect this to be solved more cleanly in drivers/gpu/drm, but I don't know where to look for that code. Arnd
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