linux-kernel - Re: [PATCH v4 2/4] KVM: X86: Add paravirt remote TLB flush

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Message-ID: <CANRm+CxBAH5eY9d-oJW8Y2WXyyKbAZdk-=YCyQHTw2SP9c3Fqw@mail.gmail.com>
Date:   Mon, 13 Nov 2017 16:12:33 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        kvm <kvm@...r.kernel.org>, Paolo Bonzini <pbonzini@...hat.com>,
        "Radim Kr??m????" <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>
Subject: Re: [PATCH v4 2/4] KVM: X86: Add paravirt remote TLB flush

2017-11-13 15:59 GMT+08:00 Peter Zijlstra <peterz@...radead.org>:
> On Sun, Nov 12, 2017 at 04:33:24PM -0800, Wanpeng Li wrote:
>> +static void kvm_flush_tlb_others(const struct cpumask *cpumask,
>> +                     const struct flush_tlb_info *info)
>> +{
>> +     u8 state;
>> +     int cpu;
>> +     struct kvm_steal_time *src;
>> +     struct cpumask *flushmask = this_cpu_cpumask_var_ptr(__pv_tlb_mask);
>> +
>> +     if (unlikely(!flushmask))
>> +             return;
>> +
>> +     cpumask_copy(flushmask, cpumask);
>> +     /*
>> +      * We have to call flush only on online vCPUs. And
>> +      * queue flush_on_enter for pre-empted vCPUs
>> +      */
>> +     for_each_cpu(cpu, cpumask) {
>
> Should this not iterate flushmask? Its far too early to think, so I'm
> not sure this is an actual problem, but it does seem weird.

Agreed, should be flushmask in next version. :)

Regards,
Wanpeng Li

>
>> +             src = &per_cpu(steal_time, cpu);
>> +             state = READ_ONCE(src->preempted);
>> +             if ((state & KVM_VCPU_PREEMPTED)) {
>> +                     if (try_cmpxchg(&src->preempted, &state,
>> +                             state | KVM_VCPU_SHOULD_FLUSH))
>> +                             __cpumask_clear_cpu(cpu, flushmask);
>> +             }
>> +     }
>> +
>> +     native_flush_tlb_others(flushmask, info);
>> +}