Re: [PATCH v4] KVM: kvmclock: Fix vCPUs > 64 can't be online/hotpluged

[Wanpeng Li]

ping, :)
On Wed, 24 Feb 2021 at 09:38, Wanpeng Li <kernellwp@xxxxxxxxx> wrote:
>
> From: Wanpeng Li <wanpengli@xxxxxxxxxxx>
>
> # 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 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. It's broken for no-vsyscall
> and sometimes you end up with vsyscall disabled if the host does something
> strange. This patch fixes it by allocating this dynamically memory
> unconditionally even if vsyscall is disabled.
>
> Fixes: 6a1cac56f4 ("x86/kvm: Use __bss_decrypted attribute in shared variables")
> Reported-by: Zelin Deng <zelin.deng@xxxxxxxxxxxxxxxxx>
> Cc: Brijesh Singh <brijesh.singh@xxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx#v4.19-rc5+
> Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx>
> ---
> v3 -> v4:
>  * fix kernel test robot report WARNING
> v2 -> v3:
>  * allocate dynamically memory unconditionally
> v1 -> v2:
>  * add code comments
>
>  arch/x86/kernel/kvmclock.c | 19 +++++++++----------
>  1 file changed, 9 insertions(+), 10 deletions(-)
>
> diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
> index aa59374..1fc0962 100644
> --- a/arch/x86/kernel/kvmclock.c
> +++ b/arch/x86/kernel/kvmclock.c
> @@ -268,21 +268,20 @@ static void __init kvmclock_init_mem(void)
>
>  static int __init kvm_setup_vsyscall_timeinfo(void)
>  {
> -#ifdef CONFIG_X86_64
> -       u8 flags;
> +       kvmclock_init_mem();
>
> -       if (!per_cpu(hv_clock_per_cpu, 0) || !kvmclock_vsyscall)
> -               return 0;
> +#ifdef CONFIG_X86_64
> +       if (per_cpu(hv_clock_per_cpu, 0) && kvmclock_vsyscall) {
> +               u8 flags;
>
> -       flags = pvclock_read_flags(&hv_clock_boot[0].pvti);
> -       if (!(flags & PVCLOCK_TSC_STABLE_BIT))
> -               return 0;
> +               flags = pvclock_read_flags(&hv_clock_boot[0].pvti);
> +               if (!(flags & PVCLOCK_TSC_STABLE_BIT))
> +                       return 0;
>
> -       kvm_clock.vdso_clock_mode = VDSO_CLOCKMODE_PVCLOCK;
> +               kvm_clock.vdso_clock_mode = VDSO_CLOCKMODE_PVCLOCK;
> +       }
>  #endif
>
> -       kvmclock_init_mem();
> -
>         return 0;
>  }
>  early_initcall(kvm_setup_vsyscall_timeinfo);
> --
> 2.7.4
>