Re: [RFC PATCH v4 5/8] x86/mm: Introduce Remote Action Request

[Kirill A. Shutemov]

On Thu, Jun 26, 2025 at 06:41:09PM +0300, Kirill A. Shutemov wrote:
> > +	/*
> > +	 * Allow RAR events to be processed while interrupts are disabled on
> > +	 * a target CPU. This prevents "pileups" where many CPUs are waiting
> > +	 * on one CPU that has IRQs blocked for too long, and should reduce
> > +	 * contention on the rar_payload table.
> > +	 */
> > +	wrmsrl(MSR_IA32_RAR_CTRL, RAR_CTRL_ENABLE | RAR_CTRL_IGNORE_IF);
> 
> Hmm. How is RAR_CTRL_IGNORE_IF safe? Wouldn't it break GUP_fast() which
> relies on disabling interrupts to block TLB flush and page table freeing?

Ah. I missed that x86 switched to MMU_GATHER_RCU_TABLE_FREE.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov