Re: [PATCH RFC V3 00/29] Support of Virtual CPU Hotplug for ARMv8 Arch

[Gavin Shan]

Hi Salil,

On 8/8/24 9:48 AM, Salil Mehta wrote:
> >   On 8/7/24 11:27 PM, Salil Mehta wrote:
> >   >
> >   > Let me figure out this. Have you also included the below patch along
> >   > with the architecture agnostic patch-set accepted in this Qemu cycle?
> >   >
> >   > https://lore.kernel.org/all/20240801142322.3948866-3-peter.maydell@lin
> >   > aro.org/
> >   >
> >   
> >   There are no vCPU fd to be parked and unparked when the core dump
> >   happenes. I tried it, but didn't help. I added more debugging messages and
> >   the core dump is triggered in the following path. It seems 'cpu-
> >   >sve_vq.map' isn't correct since it's populated in CPU realization path, and
> >   those non-cold-booted CPUs aren't realized in the booting stage.
>
>
> Ah, I've to fix the SVE support. I'm already working on it and will be part of
> the RFC V4.
>
> Have you tried booting VM by disabling the SVE support?

I'm able to boot the guest after SVE is disabled by clearing the corresponding
bits in ID_AA64PFR0, as below.

static bool kvm_arm_get_host_cpu_features(ARMHostCPUFeatures *ahcf)
{
    :

    /*
     * SVE is explicitly disabled. Otherwise, the non-cold-booted
     * CPUs can't be initialized in the vCPU hotplug scenario.
     */
    err = read_sys_reg64(fdarray[2], &ahcf->isar.id_aa64pfr0,
                         ARM64_SYS_REG(3, 0, 0, 4, 0));
    ahcf->isar.id_aa64pfr0 &= ~R_ID_AA64PFR0_SVE_MASK;
}

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 ]---

Thanks,
Gavin