Hi, I have discovered a regression in recent kernels that causes Xen PV DomU guests to be limited to a single vCPU, despite multiple vCPUs being configured. This issue does no occur in version 6.6.
After bisecting, I identified the regression was introduce in kernel 6.9 in a commit that limits the number of possible CPUs to 1 when APIC is disabled [1]. However, Xen PV guests always disable APIC, leading to incorrect CPU limitation. Following patch resolves this issue by skipping apic_is_disabled check for Xen PV guests. I believe it makes sense to backport this fix to stable versions, so I'm Ccing sta...@vger.kernel.org (as per [2]). Note that there is a minor conflict in both applicable versions (6.12 and 6.13). Please, let me know if a different approach would be preferred. [1] https://lore.kernel.org/r/20240213210252.290098...@linutronix.de [2] https://docs.kernel.org/process/stable-kernel-rules.html#option-1 Thanks, Petr Petr Vaněk (1): x86/cpu/topology: Don't limit CPUs to 1 for Xen PV guests due to disabled APIC arch/x86/kernel/cpu/topology.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) -- 2.48.1
