Re: [Xen-devel] [PATCH] Remove a set operation for VCPU_KICK_SOFTIRQ when post interrupt to vm.

["Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx>]

Jan Beulich wrote on 2015-09-23:
>>>> On 23.09.15 at 05:50, <yang.z.zhang@xxxxxxxxx> wrote:
>> --- a/xen/arch/x86/hvm/vmx/vmx.c
>> +++ b/xen/arch/x86/hvm/vmx/vmx.c
>> @@ -1678,8 +1678,9 @@ static void __vmx_deliver_posted_interrupt(struct
> vcpu *v)
>>      {
>>          unsigned int cpu = v->processor;
>> -        if ( !test_and_set_bit(VCPU_KICK_SOFTIRQ,
>> &softirq_pending(cpu)) -             && (cpu != smp_processor_id()) ) +
>>        if ( !test_bit(VCPU_KICK_SOFTIRQ, &softirq_pending(cpu)) +      
>>       && pi_test_on(&v->arch.hvm_vmx.pi_desc) +             && (cpu !=
>> smp_processor_id()))
>>              send_IPI_mask(cpumask_of(cpu), posted_intr_vector);
>>      }
>>  }
> 
> So this still removes the setting of the softirq - how can that be
> correct (namely in the cpu == smp_processor_id() case)? Did you
> perhaps mean

Why it will cause problem? The pending interrupt is covered by the check before 
vmentry: if the outstanding bit is setting, it will redo the vmentry. So even 
there is no softirq, the pending interrupt still can be injected to guest in 
time.

--- a/xen/arch/x86/hvm/vmx/entry.S
+++ b/xen/arch/x86/hvm/vmx/entry.S
@@ -77,6 +77,9 @@ UNLIKELY_START(ne, realmode)
         call vmx_enter_realmode
 UNLIKELY_END(realmode)
 
+        bt   $0,VCPU_vmx_pi_ctrl(%rbx)
+        jc   .Lvmx_do_vmentry
+
         mov  %rsp,%rdi
         call vmx_vmenter_helper
         mov  VCPU_hvm_guest_cr2(%rbx),%rax


Best regards,
Yang



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