Re: [patch 1/3] x86/fpu: Prevent FPU state corruption

On Sun, May 01, 2022 at 09:31:43PM +0200, Thomas Gleixner wrote:

The latter is checking whether some other context already uses FPU in the kernel, but if that's not the case then it allows FPU to be used unconditionally even if the calling context interupted a fpregs_lock()

Unknown word [interupted] in commit message. Suggestions: ['interrupted', ...

/*

• Can we use the FPU in kernel mode with the
• whole "kernel_fpu_begin/end()" sequence?

While at it, drop the "we": "Can the FPU be used in kernel mode... "

• • It's always ok in process context (ie "not interrupt")
• • but it is sometimes ok even from an irq.
  */

bool irq_fpu_usable(void) {

• return !in_interrupt() ||

• interrupted_user_mode() ||
  

• interrupted_kernel_fpu_idle();
  

• if (WARN_ON_ONCE(in_nmi()))

• return false;
  

• /* In kernel FPU usage already active? */
• if (this_cpu_read(in_kernel_fpu))

• return false;
  

• /*

• * When not in NMI or hard interrupt context, FPU can be used:
  

"... can be used in:"

• *
  

• * - Task context is safe except from within fpregs_lock()'ed
  

• *   critical regions.
  

• *
  

• * - Soft interrupt processing context which cannot happen
  

• *   while in a fpregs_lock()'ed critical region.
  

But those are only nitpicks. With those fixed:

Reviewed-by: Borislav Petkov bp@suse.de

Thx.