On Wed, 22 Oct 2025 19:37:27 -1000 Linus Torvalds <[email protected]> wrote:
> On Wed, 22 Oct 2025 at 14:05, Kuniyuki Iwashima <[email protected]> wrote: > > > > unsafe_put_user() can be used to save a stac/clac pair, but > > masked_user_access_begin() or user_access_begin() introduces > > an unnecessary address masking or access_ok(). > > > > Add a low-level helper for such a use case. > > I really suspect that you cannot actually measure the cost of the > extra masking, and would be much happier if you just used a regular > "user_access_begin()" (perhaps the "user_write_access_begin()" > variant). Or wait for scoped_user_write_access() to get committed and then use that. David > > The masking is very cheap - literally just a couple of ALU > instructions. And unless you can actually measure some real advantage > of avoiding it, let's not add another helper to this area. > > We spent a fair amount of time undoing years of "__get_user()" and > "__put_user()" cases that didn't actually help, and sometimes only > made it hard to see where the actual user pointer validation was done. > > Linus >
