Re: [PATCH v5 03/14] KVM: ARM: Initial skeleton to compile KVM support

Rusty Russell
2013-01-17T02:38:35Z

Russell King - ARM Linux <linux@arm.linux.org.uk> writes:
> On Wed, Jan 16, 2013 at 01:26:01PM +1030, Rusty Russell wrote:
>> Christoffer Dall <c.dall@virtualopensystems.com> writes:
>>
>> > On Mon, Jan 14, 2013 at 11:24 AM, Russell King - ARM Linux
>> > <linux@arm.linux.org.uk> wrote:
>> >> On Tue, Jan 08, 2013 at 01:38:55PM -0500, Christoffer Dall wrote:
>> >>> + /* -ENOENT for unknown features, -EINVAL for invalid combinations. */
>> >>> + for (i = 0; i < sizeof(init->features)*8; i++) {
>> >>> + if (init->features[i / 32] & (1 << (i % 32))) {
>> >>
>> >> Isn't this an open-coded version of test_bit() ?
>> >
>> > indeed, nicely spotted:
>>
>> BTW, I wrote it that was out of excessive paranoia: it's a userspace
>> API, and test_bit() won't be right on 64 bit BE systems.
>
> So why is this a concern for 32-bit systems (which are, by definition,
> only in arch/arm) ?

Because this feature bitmap system is the same code which other archs
*should* be using for specifying kvm cpus :)

Cheers,
Rusty.