Re: [PATCH v2] x86/idle: prevent entering C6 with in service interrupts on Intel

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 11/05/2020 11:17, Roger Pau Monne wrote:
> Apply a workaround for Intel errata CLX30: "A Pending Fixed Interrupt
> May Be Dispatched Before an Interrupt of The Same Priority Completes".
>
> It's not clear which models are affected, as the errata is listed in
> the "Second Generation Intel Xeon Scalable Processors" specification
> update, but the issue has been seen as far back as Nehalem processors.

Really?  I'm only aware of it being Haswell and later.

CLX30 was just one single example I gave you.  It is public in all the
specification updates going backwards, and is for example SKX100, BDX99 etc.

> Apply the workaround to all Intel processors, the condition can be
> relaxed later.

Nothing in the code checks ISR, so we're applying "no power saving"
unilaterally rather than in the very rare corner case that it occurs.

I'm also not aware of it affecting Atom processors.

This will cripple anything running on battery power, and is therefore
not an appropriate fix in this form.

~Andrew