On Tue, Mar 23, 2021 at 12:08:56PM +0000, Robin Murphy wrote: > On 2021-03-23 07:34, Yang Yingliang wrote: > > When copy over 128 bytes, src/dst is added after > > each ldp/stp instruction, it will cost more time. > > To improve this, we only add src/dst after load > > or store 64 bytes. > > This breaks the required behaviour for copy_*_user(), since the fault > handler expects the base address to be up-to-date at all times. Say you're > copying 128 bytes and fault on the 4th store, it should return 80 bytes not > copied; the code below would return 128 bytes not copied, even though 48 > bytes have actually been written to the destination. > > We've had a couple of tries at updating this code (because the whole > template is frankly a bit terrible, and a long way from the well-optimised > code it was derived from), but getting the fault-handling behaviour right > without making the handler itself ludicrously complex has proven tricky. And > then it got bumped down the priority list while the uaccess behaviour in > general was in flux - now that the dust has largely settled on that I should > probably try to find time to pick this up again...
I think the v5 from Oli was pretty close, but it didn't get any review: https://lore.kernel.org/r/20200914151800.2270-1-oli.sw...@arm.com he also included tests: https://lore.kernel.org/r/20200916104636.19172-1-oli.sw...@arm.com It would be great if you or somebody else has time to revive those! Will
