Re: [PATCH] kvm: x86: simplify kvm_vector_to_index()

[Juergen Gross]

On 20.08.25 15:42, Yury Norov wrote:
> On Tue, Aug 19, 2025 at 04:12:11PM -0700, Sean Christopherson wrote:
> > On Sat, 19 Jul 2025 21:58:45 -0400, Yury Norov wrote:
> > > Use find_nth_bit() and make the function almost a one-liner.
> >
> > Applied to kvm-x86 misc, thanks!
> >
> > P.S. I'm amazed you could decipher the intent of the code.  Even with your
> >       patch, it took me 10+ minutes to understand the "logic".
>
> Thanks Sean. :)
>
> > [1/1] kvm: x86: simplify kvm_vector_to_index()
> >        https://github.com/kvm-x86/linux/commit/cc63f918a215

Is this really correct?

The original code has:

	for (i = 0; i <= mod; i++)

(note the "<=").

So it will find the (mod + 1)th bit set, so shouldn't it use

	idx = find_nth_bit(bitmap, bitmap_size, (vector % dest_vcpus) + 1);

instead?

My remark assumes that find_nth_bit(bitmap, bitmap_size, 1) will return the
same value as find_first_bit(bitmap, bitmap_size).


Juergen

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