[PATCH] x86/uaccess: Avoid barrier_nospec() in copy_from_user()

[Kirill A. Shutemov]

On Mon, Oct 28, 2024 at 08:44:10AM -1000, Linus Torvalds wrote:
> I The *hardware* presumably uses either bit 47/56 because that's the
> actual hardware width of the TLB / cache matching.

It is a guess, right?

The bug makes more sense to me if the bit number depends on the active
paging mode: this bit naturally used for indexing in top level page table.
The mistake is more understandable this way.

> So no. We're not replacing one simple microarchitectural assumption
> (sign bit is sufficient for safety) with another more complicated one
> (bit X is sufficient for safety).

Okay, fair enough.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov