Re: [PATCH v2] KVM: kvmclock: Fix vCPUs > 64 can't be online/hotpluged

[Wanpeng Li]

On Wed, 27 Jan 2021 at 08:28, Wanpeng Li <kernellwp@xxxxxxxxx> wrote:
>
> On Wed, 27 Jan 2021 at 01:26, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
> >
> > On 26/01/21 02:28, Wanpeng Li wrote:
> > > ping，
> > > On Mon, 18 Jan 2021 at 17:08, Wanpeng Li <kernellwp@xxxxxxxxx> wrote:
> > >>
> > >> From: Wanpeng Li <wanpengli@xxxxxxxxxxx>
> > >>
> > >> The per-cpu vsyscall pvclock data pointer assigns either an element of the
> > >> static array hv_clock_boot (#vCPU <= 64) or dynamically allocated memory
> > >> hvclock_mem (vCPU > 64), the dynamically memory will not be allocated if
> > >> kvmclock vsyscall is disabled, this can result in cpu hotpluged fails in
> > >> kvmclock_setup_percpu() which returns -ENOMEM. This patch fixes it by not
> > >> assigning vsyscall pvclock data pointer if kvmclock vdso_clock_mode is not
> > >> VDSO_CLOCKMODE_PVCLOCK.
> >
> > I am sorry, I still cannot figure out this patch.
> >
> > Is hotplug still broken if kvm vsyscall is enabled?
>
> Just when kvm vsyscall is disabled. :)
>
> # lscpu
> Architecture:           x86_64
> CPU op-mode(s):    32-bit, 64-bit
> Byte Order:             Little Endian
> CPU(s):                   88
> On-line CPU(s) list:   0-63
> Off-line CPU(s) list:  64-87
>
> # cat /proc/cmdline
> BOOT_IMAGE=/vmlinuz-5.10.0-rc3-tlinux2-0050+ root=/dev/mapper/cl-root
> ro rd.lvm.lv=cl/root rhgb quiet console=ttyS0 LANG=en_US
> .UTF-8 no-kvmclock-vsyscall
>
> # echo 1 > /sys/devices/system/cpu/cpu76/online
> -bash: echo: write error: Cannot allocate memory

The original bug report is here.
https://bugzilla.kernel.org/show_bug.cgi?id=210213

    Wanpeng