Re: [PATCH 3/3] KVM: x86/vPMU: Add lazy mechanism to release perf_event per vPMC

[Peter Zijlstra]

On Wed, Oct 09, 2019 at 11:21:30AM +0200, Paolo Bonzini wrote:
> On 09/10/19 10:16, Peter Zijlstra wrote:

> >> bool bitfields preserve the magic behavior where something like this:
> >>
> >>   foo->x = y;
> >>
> >> (x is a bool bitfield) would be compiled as
> >>
> >>   foo->x = (y != 0);
> > 
> > This is confusion; if y is a single bit bitfield, then there is
> > absolutely _NO_ difference between these two expressions.
> 
> y is not in a struct so it cannot be a single bit bitfield. :) If y is
> an int and foo->x is a bool bitfield, you get the following:
> 
> 	foo->x = 6;	/* foo->x is 1, it would be 0 for int:1 */
> 	foo->x = 7;	/* foo->x is 1, it would be 1 for int:1 */
> 

Urgh, reading hard. You're right!