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

[Paolo Bonzini]

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?

Paolo

> > Fixes: 6a1cac56f4 ("x86/kvm: Use __bss_decrypted attribute in shared variables")
> > Reported-by: Zelin Deng <zelin.deng@xxxxxxxxxxxxxxxxx>
> > Tested-by: Haiwei Li <lihaiwei@xxxxxxxxxxx>
> > Cc: Brijesh Singh <brijesh.singh@xxxxxxx>
> > Cc: stable@xxxxxxxxxxxxxxx#v4.19-rc5+
> > Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx>
> > ---
> > v1 -> v2:
> >   * add code comments
> >
> >   arch/x86/kernel/kvmclock.c | 6 ++++--
> >   1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
> > index aa59374..01d4e55c 100644
> > --- a/arch/x86/kernel/kvmclock.c
> > +++ b/arch/x86/kernel/kvmclock.c
> > @@ -294,9 +294,11 @@ static int kvmclock_setup_percpu(unsigned int cpu)
> >          /*
> >           * The per cpu area setup replicates CPU0 data to all cpu
> >           * pointers. So carefully check. CPU0 has been set up in init
> > -        * already.
> > +        * already. Assign vsyscall pvclock data pointer iff kvmclock
> > +        * vsyscall is enabled.
> >           */
> > -       if (!cpu || (p && p != per_cpu(hv_clock_per_cpu, 0)))
> > +       if (!cpu || (p && p != per_cpu(hv_clock_per_cpu, 0)) ||
> > +           (kvm_clock.vdso_clock_mode != VDSO_CLOCKMODE_PVCLOCK))
> >                  return 0;
> >
> >          /* Use the static page for the first CPUs, allocate otherwise */
> > --
> > 2.7.4