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SubjectRe: [PATCH 7/8] KVM: x86: avoid logical_map when it is invalid
2015-01-30 10:38+0100, Paolo Bonzini:
> On 29/01/2015 22:48, Radim Krčmář wrote:
> > + if (hweight8(new->mode) != 1)
>
> Better (more optimized):
>
> if (new->mode & (new->mode - 1))

True, hweight needs to have X86_FEATURE_POPCNT to be efficient ...

Do you know of a difference with it?
new->mode & (new->mode - 1) | hweight8(new->mode) != 1
lea -0x1(%rax),%edi | popcnt %edi,%eax
test %eax,%edi | cmp $1,%eax

> Please add a comment to kvm_irq_delivery_to_apic_fast to explain what
> you are doing.

Would naming it kvm_apic_need_slow_delivery(), or something, be enough?

> > + if (hweight8(map->mode) != 1) {
> > + /* Not deliverable with optimized map. */
> > + ret = false;
> > + goto out;
> > + }
>
> Put this before the computation of cid and mda. The cid and mda are all
> wrong with a mixed map, and the result of the "if" before is influenced
> by the wrong cid. Fixed by patch 8, but better get it right here.

Will do,

thanks.


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