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

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Date:   Tue, 26 Jan 2021 18:26:33 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>,
        LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>
Cc:     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 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?

Paolo

>> Fixes: 6a1cac56f4 ("x86/kvm: Use __bss_decrypted attribute in shared variables")
>> Reported-by: Zelin Deng <zelin.deng@...ux.alibaba.com>
>> Tested-by: Haiwei Li <lihaiwei@...cent.com>
>> Cc: Brijesh Singh <brijesh.singh@....com>
>> Cc: stable@...r.kernel.org#v4.19-rc5+
>> Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
>> ---
>> 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
>>
>