Re: [PATCH] sched/x86: Save [ER]FLAGS on context switch

[Andy Lutomirski]

> On Feb 15, 2019, at 9:40 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> 
>> On Fri, Feb 15, 2019 at 09:18:00AM -0800, Linus Torvalds wrote:
>>> On Thu, Feb 14, 2019 at 11:34 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>>> 
>>> Something like the below, right?
>>> 
>>> +       frame->flags = 0;
>>> +       frame->flags = 0;
>> 
>> Those are not valid flag values.
>> 
>> Can you popf them? Yes.
>> 
>> Do they make sense? No.
>> 
>> It has the IF flag clear, for example. Is that intentional? If it is,
> 
> Uhmm. yeah, that's bonkers. We should have interrupts disabled here.
> I'll go read up on the eflags and figure out what they _should_ be right
> about there.

And probably add a comment near the POPF explaining that it will keep IRQs off :)