Re: [Xen-devel] [PATCH-for-4.9 v1 8/8] x86/hvm: serialize trap injecting producer and consumer

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

On 11/18/2016 07:14 PM, Paul Durrant wrote:
> Since injection works on a remote vCPU, and since there's no
> enforcement of the subject vCPU being paused, there's a potential race
> between the producing and consuming sides. Fix this by leveraging the
> vector field as synchronization variable.
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> [re-based]
> Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
> ---
> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
>  xen/arch/x86/hvm/dm.c         | 5 ++++-
>  xen/arch/x86/hvm/hvm.c        | 7 ++++---
>  xen/include/asm-x86/hvm/hvm.h | 2 ++
>  3 files changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/xen/arch/x86/hvm/dm.c b/xen/arch/x86/hvm/dm.c
> index ee0aeed..45e164e 100644
> --- a/xen/arch/x86/hvm/dm.c
> +++ b/xen/arch/x86/hvm/dm.c
> @@ -300,13 +300,16 @@ static int dm_op_inject_trap(struct domain *d, unsigned 
> int vcpuid,
>      if ( vcpuid >= d->max_vcpus || (v = d->vcpu[vcpuid]) == NULL )
>          return -EINVAL;
>  
> -    if ( v->arch.hvm_vcpu.inject_trap.vector != -1 )
> +    if ( cmpxchg(&v->arch.hvm_vcpu.inject_trap.vector,
> +                 HVM_TRAP_VECTOR_UNSET, HVM_TRAP_VECTOR_UPDATING) !=
> +         HVM_TRAP_VECTOR_UNSET )
>          return -EBUSY;
>  
>      v->arch.hvm_vcpu.inject_trap.type = type;
>      v->arch.hvm_vcpu.inject_trap.insn_len = insn_len;
>      v->arch.hvm_vcpu.inject_trap.error_code = error_code;
>      v->arch.hvm_vcpu.inject_trap.cr2 = cr2;
> +    smp_wmb();
>      v->arch.hvm_vcpu.inject_trap.vector = vector;
>  
>      return 0;
> diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
> index 90c4b43..f817c32 100644
> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -533,10 +533,11 @@ void hvm_do_resume(struct vcpu *v)
>      }
>  
>      /* Inject pending hw/sw trap */
> -    if ( v->arch.hvm_vcpu.inject_trap.vector != -1 )
> +    if ( v->arch.hvm_vcpu.inject_trap.vector >= 0 )
>      {
> +        smp_rmb();
>          hvm_inject_trap(&v->arch.hvm_vcpu.inject_trap);
> -        v->arch.hvm_vcpu.inject_trap.vector = -1;
> +        v->arch.hvm_vcpu.inject_trap.vector = HVM_TRAP_VECTOR_UNSET;
>      }
>  }

Does this mean I should rebase my vm_event patch?


Thanks,
Razvan

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