Re: [PATCH 1/2] x86/cpu: fix BSP detection when running as Xen PV guest

From: Jürgen Groß
Date: Thu May 02 2024 - 08:32:28 EST


On 30.04.24 18:13, Thomas Gleixner wrote:
On Fri, Apr 05 2024 at 14:34, Juergen Gross wrote:
When booting as a Xen PV guest the boot processor isn't detected
correctly and the following message is shown:

CPU topo: Boot CPU APIC ID not the first enumerated APIC ID: 0 > 1

Additionally this results in one CPU being ignored.

Fix that by calling the BSP detection logic when registering the boot
CPU's APIC, too.

Fixes: 5c5682b9f87a ("x86/cpu: Detect real BSP on crash kernels")
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
arch/x86/kernel/cpu/topology.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/topology.c b/arch/x86/kernel/cpu/topology.c
index aaca8d235dc2..23c3db5e6396 100644
--- a/arch/x86/kernel/cpu/topology.c
+++ b/arch/x86/kernel/cpu/topology.c
@@ -255,7 +255,7 @@ void __init topology_register_boot_apic(u32 apic_id)
WARN_ON_ONCE(topo_info.boot_cpu_apic_id != BAD_APICID);
topo_info.boot_cpu_apic_id = apic_id;
- topo_register_apic(apic_id, CPU_ACPIID_INVALID, true);
+ topology_register_apic(apic_id, CPU_ACPIID_INVALID, true);

No. This does not fix anything at all. It just papers over the
underlying problem.

Thanks,

tglx
---
diff --git a/arch/x86/xen/smp_pv.c b/arch/x86/xen/smp_pv.c
index 27d1a5b7f571..ac41d83b38d3 100644
--- a/arch/x86/xen/smp_pv.c
+++ b/arch/x86/xen/smp_pv.c
@@ -154,9 +154,9 @@ static void __init xen_pv_smp_config(void)
u32 apicid = 0;
int i;
- topology_register_boot_apic(apicid++);
+ topology_register_boot_apic(apicid);
- for (i = 1; i < nr_cpu_ids; i++)
+ for (i = 0; i < nr_cpu_ids; i++)
topology_register_apic(apicid++, CPU_ACPIID_INVALID, true);
/* Pretend to be a proper enumerated system */



Thanks, works great.

Do you want it to send as your patch, or should I add your Signed-off-by or
your Suggested-by?


Juergen