Re: [PATCH v3 2/6] x86/uaccess: Avoid barrier_nospec() in 64-bit __get_user()

[Josh Poimboeuf]

On Mon, Oct 28, 2024 at 06:56:15PM -0700, Josh Poimboeuf wrote:
> The barrier_nospec() in 64-bit __get_user() is slow.  Instead use
> pointer masking to force the user pointer to all 1's if a previous
> access_ok() mispredicted true for an invalid address.

Linus pointed out that __get_user() may be used by some code to access
both kernel and user space and in fact I found one such usage in
vc_read_mem()....

So I self-NAK this patch for now.

Still, it would be great if patch 1 could get merged as that gives a
significant performance boost.

-- 
Josh