Re: [Xen-devel] [PATCH 0/4] CPU hotplug port from qemu-traditionnal to qemu-xen for 4.3.

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

On 03/06/13 09:41, Ian Campbell wrote:
>> > BUG: There is an issue with SeaBIOS (used with qemu-xen). At SMP
>> > initialisation, SeaBIOS will count the number of CPU running, and the 
>> > number is
>> > always equal to maxvcpu when SeaBIOS expect less. This happen when we have
>> > something like:
>> > vcpus = 2
>> > maxvcpus = 8
>> > in the VM config file. Linux is fine with this and will use only $vcpus.  
>> > So
>> > the probleme is: an infinit loop in SeaBIOS.
> I'm a bit confused -- if SeaBIOS has an infinite loop how do you even
> get to know Linux is OK?
> 
> Do you have a fix for SeaBIOS, I don't see it in this series.

The thing is, I don't know how to fix this bug.  This is why there is no
patch.

The probleme is this loop:
> u8 cmos_smp_count = inb_cmos(CMOS_BIOS_SMP_COUNT);
> while (cmos_smp_count + 1 != readl(&CountCPUs))
>   ;

where CountCPUs is incremented by each CPU by a small piece of code and
cmos_smp_count is equal to 1, which is the number of expected vcpus-1.
CountCPUs always go up to maxvcpus under Xen.

I could simply replace the '!=' by a '>' but it feel like a workaround...

-- 
Anthony PERARD

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