Yes, I saw the problem with 3.0.13. Thanks!
Gabe
On Mon, Jan 23, 2012 at 11:40 PM, Sasha Levin <levinsasha928@xxxxxxxxx> wrote:
> The GET_SUPPORTED_CPUID bug has been fixed and shouldn't be happening
> from v3.2 onwards.
>
> Do you still see the issue in older versions?
>
> On Mon, 2012-01-23 at 21:20 -0800, Gabe Black wrote:
>> Sorry, forgot to add a subject.
>>
>> Gabe
>>
>> On Mon, Jan 23, 2012 at 9:18 PM, Gabe Black <gabeblack@xxxxxxxxxx> wrote:
>> > Hi, I think I've tracked down the bug that causes
>> > "KVM_GET_SUPPORTED_CPUID failed: Argument list too long" errors when
>> > using the kvm tool. Basically, this (possibly squished) code seems to
>> > be to blame:
>> >
>> > case 0xd: {
>> > int i;
>> >
>> > entry->flags |= KVM_CPUID_FLAG_SIGNIFCANT_INDEX;
>> > for (i = 1; *nent < maxnent && i < 64; ++i) {
>> > if (entry[i].eax == 0)
>> > continue;
>> > do_cpuid_1_ent(&entry[i], function, i);
>> > entry[i].flags |=
>> > KVM_CPUID_FLAG_SIGNIFCANT_INDEX;
>> > ++*nent;
>> > }
>> > break;
>> > }
>> >
>> > You can see there's a check whether entry[i].eax is 0, but it isn't
>> > until the next line that entry[i] is actually filled in. That means
>> > that whether or not an entry is filled in for the 0xd function is
>> > essentially random, and that can lead to the loss of valid entries. It
>> > also means that nent may be incremented too often, and since all 64
>> > entries are iterated over, that can fill up the available storage and
>> > cause that error.
>> >
>> > I tested my theory by commenting out the if (100% failure rate) and
>> > moving it after do_cpuid_1_ent (100% success rate). Since this is a
>> > non-deterministic failure that isn't really conclusive, but I'm fairly
>> > confident my fix is correct. I don't know exactly what your procedure
>> > is for submitting patches, but one is attached.
>> >
>> > Gabe
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>
>
> --
>
> Sasha.
>
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