Re: [Xen-devel] [PATCH v7 06/11] x86, paravirt: Add interface to support kvm/xen vcpu preempted check

[Pan Xinhui <xinhui@xxxxxxxxxxxxxxxxxx>]

在 2016/11/15 23:47, Peter Zijlstra 写道:
> On Wed, Nov 02, 2016 at 05:08:33AM -0400, Pan Xinhui wrote:
> > diff --git a/arch/x86/include/asm/paravirt_types.h 
> > b/arch/x86/include/asm/paravirt_types.h
> > index 0f400c0..38c3bb7 100644
> > --- a/arch/x86/include/asm/paravirt_types.h
> > +++ b/arch/x86/include/asm/paravirt_types.h
> > @@ -310,6 +310,8 @@ struct pv_lock_ops {
> >
> >         void (*wait)(u8 *ptr, u8 val);
> >         void (*kick)(int cpu);
> > +
> > +       bool (*vcpu_is_preempted)(int cpu);
> >  };
> So that ends up with a full function call in the native case. I did
> something like the below on top, completely untested, not been near a
> compiler etc..
Hi, Peter.
        I think we can avoid a function call in a simpler way. How about below

static inline bool vcpu_is_preempted(int cpu)
{
        /* only set in pv case*/
        if (pv_lock_ops.vcpu_is_preempted)
                return pv_lock_ops.vcpu_is_preempted(cpu);
        return false;
}


> It doesn't get rid of the branch, but at least it avoids the function
> call, and hardware should have no trouble predicting a constant
> condition.
>
> Also, it looks like you end up not setting vcpu_is_preempted when KVM
> doesn't support steal clock, which would end up in an instant NULL
> deref. Fixed that too.
maybe not true. There is .vcpu_is_preempted = native_vcpu_is_preempted when we 
define pv_lock_ops.

your patch is a good example for any people who want to add any native/pv 
function. :)

thanks
xinhui

> ---
> --- a/arch/x86/include/asm/paravirt.h
> +++ b/arch/x86/include/asm/paravirt.h
> @@ -673,6 +673,11 @@ static __always_inline void pv_kick(int
>         PVOP_VCALL1(pv_lock_ops.kick, cpu);
>  }
>
> +static __always_inline void pv_vcpu_is_prempted(int cpu)
> +{
> +       PVOP_VCALLEE1(pv_lock_ops.vcpu_is_preempted, cpu);
> +}
> +
>  #endif /* SMP && PARAVIRT_SPINLOCKS */
>
>  #ifdef CONFIG_X86_32
> --- a/arch/x86/include/asm/paravirt_types.h
> +++ b/arch/x86/include/asm/paravirt_types.h
> @@ -309,7 +309,7 @@ struct pv_lock_ops {
>         void (*wait)(u8 *ptr, u8 val);
>         void (*kick)(int cpu);
>
> -       bool (*vcpu_is_preempted)(int cpu);
> +       struct paravirt_callee_save vcpu_is_preempted;
>  };
>
>  /* This contains all the paravirt structures: we get a convenient
> --- a/arch/x86/include/asm/qspinlock.h
> +++ b/arch/x86/include/asm/qspinlock.h
> @@ -32,6 +32,12 @@ static inline void queued_spin_unlock(st
>  {
>         pv_queued_spin_unlock(lock);
>  }
> +
> +#define vcpu_is_preempted vcpu_is_preempted
> +static inline bool vcpu_is_preempted(int cpu)
> +{
> +       return pv_vcpu_is_preempted(cpu);
> +}
>  #else
>  static inline void queued_spin_unlock(struct qspinlock *lock)
>  {
> --- a/arch/x86/include/asm/spinlock.h
> +++ b/arch/x86/include/asm/spinlock.h
> @@ -26,14 +26,6 @@
>  extern struct static_key paravirt_ticketlocks_enabled;
>  static __always_inline bool static_key_false(struct static_key *key);
>
> -#ifdef CONFIG_PARAVIRT_SPINLOCKS
> -#define vcpu_is_preempted vcpu_is_preempted
> -static inline bool vcpu_is_preempted(int cpu)
> -{
> -       return pv_lock_ops.vcpu_is_preempted(cpu);
> -}
> -#endif
> -
>  #include <asm/qspinlock.h>
>
>  /*
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -415,15 +415,6 @@ void kvm_disable_steal_time(void)
>         wrmsr(MSR_KVM_STEAL_TIME, 0, 0);
>  }
>
> -static bool kvm_vcpu_is_preempted(int cpu)
> -{
> -       struct kvm_steal_time *src;
> -
> -       src = &per_cpu(steal_time, cpu);
> -
> -       return !!src->preempted;
> -}
> -
>  #ifdef CONFIG_SMP
>  static void __init kvm_smp_prepare_boot_cpu(void)
>  {
> @@ -480,9 +471,6 @@ void __init kvm_guest_init(void)
>         if (kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) {
>                 has_steal_clock = 1;
>                 pv_time_ops.steal_clock = kvm_steal_clock;
> -#ifdef CONFIG_PARAVIRT_SPINLOCKS
> -               pv_lock_ops.vcpu_is_preempted = kvm_vcpu_is_preempted;
> -#endif
>         }
>
>         if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
> @@ -604,6 +592,14 @@ static void kvm_wait(u8 *ptr, u8 val)
>         local_irq_restore(flags);
>  }
>
> +static bool __kvm_vcpu_is_preempted(int cpu)
> +{
> +       struct kvm_steal_time *src = &per_cpu(steal_time, cpu);
> +
> +       return !!src->preempted;
> +}
> +PV_CALLEE_SAVE_REGS_THUNK(__kvm_vcpu_is_preempted);
> +
>  /*
>   * Setup pv_lock_ops to exploit KVM_FEATURE_PV_UNHALT if present.
>   */
> @@ -620,6 +616,12 @@ void __init kvm_spinlock_init(void)
>         pv_lock_ops.queued_spin_unlock = 
> PV_CALLEE_SAVE(__pv_queued_spin_unlock);
>         pv_lock_ops.wait = kvm_wait;
>         pv_lock_ops.kick = kvm_kick_cpu;
> +       pv_lock_ops.vcpu_is_preempted = 
> PV_CALLEE_SAVE(__native_vcpu_is_preempted);
> +
> +       if (kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) {
> +               pv_lock_ops.vcpu_is_preempted =
> +                       PV_CALLEE_SAVE(__kvm_vcpu_is_preempted);
> +       }
>  }
>
>  static __init int kvm_spinlock_init_jump(void)
> --- a/arch/x86/kernel/paravirt-spinlocks.c
> +++ b/arch/x86/kernel/paravirt-spinlocks.c
> @@ -12,7 +12,6 @@ __visible void __native_queued_spin_unlo
>  {
>         native_queued_spin_unlock(lock);
>  }
> -
>  PV_CALLEE_SAVE_REGS_THUNK(__native_queued_spin_unlock);
>
>  bool pv_is_native_spin_unlock(void)
> @@ -21,9 +20,16 @@ bool pv_is_native_spin_unlock(void)
>                 __raw_callee_save___native_queued_spin_unlock;
>  }
>
> -static bool native_vcpu_is_preempted(int cpu)
> +__visible bool __native_vcpu_is_preempted(int cpu)
>  {
> -       return 0;
> +       return false;
> +}
> +PV_CALLEE_SAVE_REGS_THUNK(__native_vcpu_is_preempted);
> +
> +bool pv_is_native_vcpu_is_preempted(void)
> +{
> +       return pv_lock_ops.queued_spin_unlock.func ==
> +               __raw_callee_save__native_vcpu_is_preempted;
>  }
copy-paste issue...

>  struct pv_lock_ops pv_lock_ops = {
> @@ -32,7 +38,7 @@ struct pv_lock_ops pv_lock_ops = {
>         .queued_spin_unlock = PV_CALLEE_SAVE(__native_queued_spin_unlock),
>         .wait = paravirt_nop,
>         .kick = paravirt_nop,
> -       .vcpu_is_preempted = native_vcpu_is_preempted,
> +       .vcpu_is_preempted = PV_CALLEE_SAVE(__native_vcpu_is_preempted),
>  #endif /* SMP */
>  };
>  EXPORT_SYMBOL(pv_lock_ops);
> --- a/arch/x86/kernel/paravirt_patch_32.c
> +++ b/arch/x86/kernel/paravirt_patch_32.c
> @@ -11,6 +11,7 @@ DEF_NATIVE(pv_mmu_ops, read_cr3, "mov %c
>
>  #if defined(CONFIG_PARAVIRT_SPINLOCKS)
>  DEF_NATIVE(pv_lock_ops, queued_spin_unlock, "movb $0, (%eax)");
> +DEF_NATIVE(pv_lock_ops, vcpu_is_preempted, "movl $0, %eax");
>  #endif
>
>  unsigned paravirt_patch_ident_32(void *insnbuf, unsigned len)
> @@ -26,6 +27,7 @@ unsigned paravirt_patch_ident_64(void *i
>  }
>
>  extern bool pv_is_native_spin_unlock(void);
> +extern bool pv_is_native_vcpu_is_preempted(void);
>
>  unsigned native_patch(u8 type, u16 clobbers, void *ibuf,
>                       unsigned long addr, unsigned len)
> @@ -54,6 +56,12 @@ unsigned native_patch(u8 type, u16 clobb
>                                 end   = end_pv_lock_ops_queued_spin_unlock;
>                                 goto patch_site;
>                         }
> +               case PARAVIRT_PATCH(pv_lock_ops.vcpu_is_preempted):
> +                       if (pv_is_native_vcpu_is_preempted()) {
> +                               start = start_pv_lock_ops_vcpu_is_preempted;
> +                               end   = end_pv_lock_ops_vcpu_is_preempted;
> +                               goto patch_site;
> +                       }
>  #endif
>
>         default:
> --- a/arch/x86/kernel/paravirt_patch_64.c
> +++ b/arch/x86/kernel/paravirt_patch_64.c
> @@ -20,6 +20,7 @@ DEF_NATIVE(, mov64, "mov %rdi, %rax");
>
>  #if defined(CONFIG_PARAVIRT_SPINLOCKS)
>  DEF_NATIVE(pv_lock_ops, queued_spin_unlock, "movb $0, (%rdi)");
> +DEF_NATIVE(pv_lock_ops, vcpu_is_preempted, "movl $0, rax");
>  #endif
>
>  unsigned paravirt_patch_ident_32(void *insnbuf, unsigned len)
> @@ -35,6 +36,7 @@ unsigned paravirt_patch_ident_64(void *i
>  }
>
>  extern bool pv_is_native_spin_unlock(void);
> +extern bool pv_is_native_vcpu_is_preempted(void);
>
>  unsigned native_patch(u8 type, u16 clobbers, void *ibuf,
>                       unsigned long addr, unsigned len)
> @@ -66,6 +68,12 @@ unsigned native_patch(u8 type, u16 clobb
>                                 end   = end_pv_lock_ops_queued_spin_unlock;
>                                 goto patch_site;
>                         }
> +               case PARAVIRT_PATCH(pv_lock_ops.vcpu_is_preempted):
> +                       if (pv_is_native_vcpu_is_preempted()) {
> +                               start = start_pv_lock_ops_vcpu_is_preempted;
> +                               end   = end_pv_lock_ops_vcpu_is_preempted;
> +                               goto patch_site;
> +                       }
>  #endif
>
>         default:
> --- a/arch/x86/xen/spinlock.c
> +++ b/arch/x86/xen/spinlock.c
> @@ -114,6 +114,8 @@ void xen_uninit_lock_cpu(int cpu)
>         per_cpu(irq_name, cpu) = NULL;
>  }
>
> +PV_CALLEE_SAVE_REGS_THUNK(xen_vcpu_stolen);
> +
>  /*
>   * Our init of PV spinlocks is split in two init functions due to us
>   * using paravirt patching and jump labels patching and having to do
> @@ -136,8 +138,7 @@ void __init xen_init_spinlocks(void)
>         pv_lock_ops.queued_spin_unlock = 
> PV_CALLEE_SAVE(__pv_queued_spin_unlock);
>         pv_lock_ops.wait = xen_qlock_wait;
>         pv_lock_ops.kick = xen_qlock_kick;
> -
> -       pv_lock_ops.vcpu_is_preempted = xen_vcpu_stolen;
> +       pv_lock_ops.vcpu_is_preempted = PV_CALLEE_SAVE(xen_vcpu_stolen);
>  }
>
>  /*

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