Re: [patch 26/30] x86/microcode: Protect against instrumentation

[Thomas Gleixner]

On Thu, Aug 10 2023 at 22:36, Peter Zijlstra wrote:
> On Thu, Aug 10, 2023 at 08:38:04PM +0200, Thomas Gleixner wrote:
>> From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
>> 
>> The wait for control loop in which the siblings are waiting for the
>> microcode update on the primary thread must be protected against
>> instrumentation as instrumentation can end up in #INT3, #DB or #PF, which
>> then returns with IRET. That IRET reenables NMI which is the opposite of
>> what the NMI rendezvouz is trying to achieve.
>
> asm_exc_nmi will re-enable NMIs when DEBUG_ENTRY before we reach C.
> Late loading had better depend on !DEBUG_ENTRY.

Good point