On Sun, 9 Feb 2025 14:24:22 -0400 Jason Gunthorpe <jgg@xxxxxxxxxx> wrote: > On Sun, Feb 09, 2025 at 05:47:11PM +0000, David Laight wrote: > > Historiaclly the code relied on access_ok() to validate the address range. > > Commit 26f4c328079d7 added an explicit wrap check before access_ok(). > > Commit c28b1fc70390d then changed the wrap test to use check_add_overflow(). > > Commit 6014bc27561f2 relaxed the checks in x86-64's access_ok() and added > > an explicit check for TASK_SIZE here to make up for it. > > That left a pointless access_ok() call with its associated 'lfence' that > > can never actually fail. > > So just delete the test. > > > > Signed-off-by: David Laight <david.laight.linux@xxxxxxxxx> > > --- > > mm/gup.c | 4 +--- > > 1 file changed, 1 insertion(+), 3 deletions(-) > > Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx> > > I often wonder about about access_ok() calls, if they still do > anything.. They still do 'stuff' and end up containing a slow memory synchronising instruction (to avoid speculative accesses controlled by the application). But there are better ways to handle bad user pointers. So, mostly access_ok() isn't needed outside the architecture code that handles userspace accesses. David
