linux-kernel - Re: [PATCH v2] KVM: kvmclock: Fix vCPUs

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Date:   Wed, 27 Jan 2021 08:28:26 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH v2] KVM: kvmclock: Fix vCPUs > 64 can't be online/hotpluged

On Wed, 27 Jan 2021 at 01:26, Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> On 26/01/21 02:28, Wanpeng Li wrote:
> > ping，
> > On Mon, 18 Jan 2021 at 17:08, Wanpeng Li <kernellwp@...il.com> wrote:
> >>
> >> From: Wanpeng Li <wanpengli@...cent.com>
> >>
> >> 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

    Wanpeng