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From:   Wanpeng Li <kernellwp@gmail.com>
Date:   Thu, 16 Nov 2017 13:30:57 +0800
Message-ID: <CANRm+CxjUTmCtT3V0He_c-GzAUeRcc0m2e11=OxLA8-Er+pRmw@mail.gmail.com>
Subject: Re: [PATCH v5 2/4] KVM: X86: Add paravirt remote TLB flush
To:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        kvm <kvm@vger.kernel.org>
Cc:     Paolo Bonzini <pbonzini@redhat.com>,
        =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Wanpeng Li <wanpeng.li@hotmail.com>
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2017-11-13 18:01 GMT+08:00 Wanpeng Li <kernellwp@gmail.com>:
> From: Wanpeng Li <wanpeng.li@hotmail.com>
>
> Remote flushing api's does a busy wait which is fine in bare-metal
> scenario. But with-in the guest, the vcpus might have been pre-empted
> or blocked. In this scenario, the initator vcpu would end up
> busy-waiting for a long amount of time.
>
> This patch set implements para-virt flush tlbs making sure that it does
> not wait for vcpus that are sleeping. And all the sleeping vcpus flush
> the tlb on guest enter.
>
> The best result is achieved when we're overcommiting the host by running
> multiple vCPUs on each pCPU. In this case PV tlb flush avoids touching
> vCPUs which are not scheduled and avoid the wait on the main CPU.
>
> Test on a Haswell i7 desktop 4 cores (2HT), so 8 pCPUs, running ebizzy
> in one linux guest.
>
> ebizzy -M
>               vanilla    optimized     boost
>  8 vCPUs       10152       10083       -0.68%
> 16 vCPUs        1224        4866       297.5%
> 24 vCPUs        1109        3871       249%
> 32 vCPUs        1025        3375       229.3%
>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Radim Kr=C4=8Dm=C3=A1=C5=99 <rkrcmar@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
> ---
>  Documentation/virtual/kvm/cpuid.txt  |  4 ++++
>  arch/x86/include/uapi/asm/kvm_para.h |  2 ++
>  arch/x86/kernel/kvm.c                | 42 ++++++++++++++++++++++++++++++=
+++++-
>  3 files changed, 47 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/virtual/kvm/cpuid.txt b/Documentation/virtual/=
kvm/cpuid.txt
> index 117066a..9693fcc 100644
> --- a/Documentation/virtual/kvm/cpuid.txt
> +++ b/Documentation/virtual/kvm/cpuid.txt
> @@ -60,6 +60,10 @@ KVM_FEATURE_PV_DEDICATED           ||     8 || guest c=
hecks this feature bit
>                                     ||       || mizations such as usage o=
f
>                                     ||       || qspinlocks.
>  ------------------------------------------------------------------------=
------
> +KVM_FEATURE_PV_TLB_FLUSH           ||     9 || guest checks this feature=
 bit
> +                                   ||       || before enabling paravirtu=
alized
> +                                   ||       || tlb flush.
> +------------------------------------------------------------------------=
------
>  KVM_FEATURE_CLOCKSOURCE_STABLE_BIT ||    24 || host will warn if no gues=
t-side
>                                     ||       || per-cpu warps are expecte=
d in
>                                     ||       || kvmclock.
> diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi=
/asm/kvm_para.h
> index 6d66556..e267d83 100644
> --- a/arch/x86/include/uapi/asm/kvm_para.h
> +++ b/arch/x86/include/uapi/asm/kvm_para.h
> @@ -26,6 +26,7 @@
>  #define KVM_FEATURE_PV_EOI             6
>  #define KVM_FEATURE_PV_UNHALT          7
>  #define KVM_FEATURE_PV_DEDICATED       8
> +#define KVM_FEATURE_PV_TLB_FLUSH       9
>
>  /* The last 8 bits are used to indicate how to interpret the flags field
>   * in pvclock structure. If no bits are set, all flags are ignored.
> @@ -54,6 +55,7 @@ struct kvm_steal_time {
>
>  #define KVM_VCPU_NOT_PREEMPTED      (0 << 0)
>  #define KVM_VCPU_PREEMPTED          (1 << 0)
> +#define KVM_VCPU_SHOULD_FLUSH       (1 << 1)
>
>  #define KVM_CLOCK_PAIRING_WALLCLOCK 0
>  struct kvm_clock_pairing {
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index 66ed3bc..78794c1 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -465,9 +465,40 @@ static void __init kvm_apf_trap_init(void)
>         update_intr_gate(X86_TRAP_PF, async_page_fault);
>  }
>
> +static DEFINE_PER_CPU(cpumask_var_t, __pv_tlb_mask);
> +
> +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 =3D this_cpu_cpumask_var_ptr(__pv_tlb_m=
ask);
> +
> +       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, flushmask) {
> +               src =3D &per_cpu(steal_time, cpu);
> +               state =3D 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);
> +}
> +
>  void __init kvm_guest_init(void)
>  {
> -       int i;
> +       int i, cpu;
>
>         if (!kvm_para_available())
>                 return;
> @@ -484,6 +515,15 @@ void __init kvm_guest_init(void)
>                 pv_time_ops.steal_clock =3D kvm_steal_clock;
>         }
>
> +       if (kvm_para_has_feature(KVM_FEATURE_PV_TLB_FLUSH) &&
> +               !kvm_para_has_feature(KVM_FEATURE_PV_DEDICATED)) {
> +               for_each_possible_cpu(cpu) {
> +                       zalloc_cpumask_var_node(per_cpu_ptr(&__pv_tlb_mas=
k, cpu),
> +                                       GFP_KERNEL, cpu_to_node(cpu));
> +               }
> +               pv_mmu_ops.flush_tlb_others =3D kvm_flush_tlb_others;
> +       }
> +
>         if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
>                 apic_set_eoi_write(kvm_guest_apic_eoi_write);
>

Adds the below codes to fix per-cpu variable memory allocation issue.
kvm_guest_init() is called too early during boot, buddy/slab system is
not ready, I didn't find suitable memblock API, so just define
variable directly.

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 707ee68..d8fbaf5 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -465,7 +465,7 @@ static void __init kvm_apf_trap_init(void)
     update_intr_gate(X86_TRAP_PF, async_page_fault);
 }

-static DEFINE_PER_CPU(cpumask_var_t, __pv_tlb_mask);
+static DEFINE_PER_CPU(cpumask_t, __pv_tlb_mask);

 static void kvm_flush_tlb_others(const struct cpumask *cpumask,
             const struct flush_tlb_info *info)
@@ -473,7 +473,7 @@ static void kvm_flush_tlb_others(const struct
cpumask *cpumask,
     u8 state;
     int cpu;
     struct kvm_steal_time *src;
-    struct cpumask *flushmask =3D this_cpu_cpumask_var_ptr(__pv_tlb_mask);
+    cpumask_t *flushmask =3D &per_cpu(__pv_tlb_mask, smp_processor_id());

     if (unlikely(!flushmask))
         return;
@@ -498,7 +498,7 @@ static void kvm_flush_tlb_others(const struct
cpumask *cpumask,

 void __init kvm_guest_init(void)
 {
-    int i, cpu;
+    int i;

     if (!kvm_para_available())
         return;
@@ -516,13 +516,8 @@ void __init kvm_guest_init(void)
     }

     if (kvm_para_has_feature(KVM_FEATURE_PV_TLB_FLUSH) &&
-        !kvm_para_has_feature(KVM_FEATURE_PV_DEDICATED)) {
-        for_each_possible_cpu(cpu) {
-            zalloc_cpumask_var_node(per_cpu_ptr(&__pv_tlb_mask, cpu),
-                    GFP_KERNEL, cpu_to_node(cpu));
-        }
+        !kvm_para_has_feature(KVM_FEATURE_PV_DEDICATED))
         pv_mmu_ops.flush_tlb_others =3D kvm_flush_tlb_others;
-    }

     if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
         apic_set_eoi_write(kvm_guest_apic_eoi_write);

From 1584176752656017441@xxx Wed Nov 15 23:31:21 +0000 2017
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