[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: HVM guest only bring up a single vCPU

Hi Jan,

On 27/08/2021 10:26, Jan Beulich wrote:
On 26.08.2021 23:00, Julien Grall wrote:
Digging down, Linux will set smp_num_siblings to 0 (via
detect_ht_early()) and as a result will skip all the CPUs. The value is
retrieve from a CPUID leaf. So it sounds like we don't set the leaft

Xen leaves leaf 1 EBX[23:16] untouched from what the tool stack
passes. The tool stack doubles the value coming from hardware
(or qemu in your case), unless the result would overflow. Hence
it would look to me as if the value coming from qemu has got to
be zero. Which is perfectly fine if HTT is off, just that
libxenguest isn't prepared for this. Could you see whether the
patch below helps (making our hack even hackier)?

It helps. The Linux HVM domain is now able to bring up all the CPUs.


libxenguest/x86: ensure CPUID[1].EBX[32:16] is non-zero for HVM

We unconditionally set HTT, so merely doubling the value read from
hardware isn't going to be correct if that value is zero.

Reported-by: Julien Grall <julien@xxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

Feel free to add my tested-by for the patch.


[1] https://pastebin.com/WvaXiXuL

Julien Grall



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.