Hi Gavin,

>  From: Gavin Shan <gshan@redhat.com>
>  Sent: Thursday, August 8, 2024 5:15 AM
>  To: Salil Mehta <salil.mehta@huawei.com>; qemu-devel@nongnu.org;
>  qemu-arm@nongnu.org; mst@redhat.com
>  
>  Hi Salil,
>  
>  On 8/8/24 10:29 AM, Gavin Shan wrote:
>  > On 8/8/24 9:48 AM, Salil Mehta wrote:
>  >
>  > However, I'm unable to hot-add a vCPU and haven't get a chance to look
>  > at it closely.
>  >
>  > (qemu) device_add host-arm-cpu,id=cpu,socket-id=1
>  > (qemu) [  258.901027] Unable to handle kernel write to read-only
>  > memory at virtual address ffff800080fa7190 [  258.901686] Mem abort info:
>  > [  258.901889]   ESR = 0x000000009600004e [  258.902160]   EC = 0x25:
>  > DABT (current EL), IL = 32 bits [  258.902543]   SET = 0, FnV = 0 [
>  > 258.902763]   EA = 0, S1PTW = 0 [  258.902991]   FSC = 0x0e: level 2
>  > permission fault [  258.903338] Data abort info:
>  > [  258.903547]   ISV = 0, ISS = 0x0000004e, ISS2 = 0x00000000 [
>  > 258.903943]   CM = 0, WnR = 1, TnD = 0, TagAccess = 0 [  258.904304]
>  > GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0 [  258.904687] swapper
>  > pgtable: 4k pages, 48-bit VAs, pgdp=00000000b8e24000 [  258.905258]
>  > [ffff800080fa7190] pgd=10000000b95b0003, p4d=10000000b95b0003,
>  > pud=10000000b95b1003, pmd=00600000b8c00781 [  258.906026] Internal
>  > error: Oops: 000000009600004e [#1] PREEMPT SMP [  258.906474] Modules
>  linked in:
>  > [  258.906705] CPU: 0 UID: 0 PID: 29 Comm: kworker/u8:1 Not tainted
>  > 6.11.0-rc2-gavin-gb446a2dae984 #7 [  258.907338] Hardware name: QEMU
>  > KVM Virtual Machine, BIOS edk2-stable202402-prebuilt.qemu.org
>  > 02/14/2024 [  258.908009] Workqueue: kacpi_hotplug
>  > acpi_hotplug_work_fn [  258.908401] pstate: 63400005 (nZCv daif +PAN
>  > -UAO +TCO +DIT -SSBS BTYPE=--) [  258.908899] pc :
>  > register_cpu+0x140/0x290 [  258.909195] lr : register_cpu+0x128/0x290
>  > [  258.909487] sp : ffff8000817fba10 [  258.909727] x29:
>  > ffff8000817fba10 x28: 0000000000000000 x27: ffff0000011f9098 [
>  > 258.910246] x26: ffff80008167b1b0 x25: 0000000000000001 x24:
>  > ffff80008153dad0 [  258.910762] x23: 0000000000000001 x22:
>  > ffff0000ff7de210 x21: ffff8000811b9a00 [  258.911279] x20:
>  > 0000000000000000 x19: ffff800080fa7190 x18: ffffffffffffffff [
>  > 258.911798] x17: 0000000000000000 x16: 0000000000000000 x15:
>  > ffff000005a46a1c [  258.912326] x14: ffffffffffffffff x13:
>  > ffff000005a4632b x12: 0000000000000000 [  258.912854] x11:
>  > 0000000000000040 x10: 0000000000000000 x9 : ffff8000808a6cd4 [
>  > 258.913382] x8 : 0101010101010101 x7 : 7f7f7f7f7f7f7f7f x6 :
>  fefefefefefefeff [  258.913906] x5 : ffff0000053fab40 x4 : ffff0000053fa920 x3
>  : ffff0000053fabb0 [  258.914439] x2 : ffff000000de1100 x1 : ffff800080fa7190
>  x0 : 0000000000000002 [  258.914968] Call trace:
>  > [  258.915154]  register_cpu+0x140/0x290 [  258.915429]
>  > arch_register_cpu+0x84/0xd8 [  258.915726]
>  > acpi_processor_add+0x480/0x5b0 [  258.916042]
>  > acpi_bus_attach+0x1c4/0x300 [  258.916334]
>  > acpi_dev_for_one_check+0x3c/0x50 [  258.916689]
>  > device_for_each_child+0x68/0xc8 [  258.917012]
>  > acpi_dev_for_each_child+0x48/0x80 [  258.917344]
>  > acpi_bus_attach+0x84/0x300 [  258.917629]  acpi_bus_scan+0x74/0x220 [
>  > 258.917902]  acpi_scan_rescan_bus+0x54/0x88 [  258.918211]
>  > acpi_device_hotplug+0x208/0x478 [  258.918529]
>  > acpi_hotplug_work_fn+0x2c/0x50 [  258.918839]
>  > process_one_work+0x15c/0x3c0
>  [  258.919139]  worker_thread+0x2ec/0x400
>  > [  258.919417]  kthread+0x120/0x130 [  258.919658]
>  > ret_from_fork+0x10/0x20 [  258.919924] Code: 91064021 9ad72000
>  > 8b130c33 d503201f (f820327f) [  258.920373] ---[ end trace
>  > 0000000000000000 ]---
>  >
>  
>  The fix [1] is needed by the guest kernel. With this, I'm able to hot add vCPU
>  and hot remove vCPU successfully.
>  
>  [1] https://lkml.org/lkml/2024/8/8/155


Good catch in the kernel. And many thanks for fixing as well.


>  
>  Thanks,
>  Gavin
>