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

[Wanpeng Li]

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.
>
> 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
>