Re: [PATCH for 4.5] x86/VPMU: Clear last_vcpu when destroying VPMU

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

On 12/13/2014 02:08 PM, Konrad Rzeszutek Wilk wrote:
> On Fri, Dec 12, 2014 at 04:20:48PM -0500, Boris Ostrovsky wrote:
>> We need to make sure that last_vcpu is not pointing to VCPU whose
>> VPMU is being destroyed. Otherwise we may try dereference it in
>> the future, when VCPU is gone.
>>
>> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> Release-Acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

I would like to send a slightly better patch on Monday (along the same 
lines but trying to avoid unnecessary IPIs if not needed).

-boris


>> ---
>>   xen/arch/x86/hvm/vpmu.c |   22 ++++++++++++++++++++++
>>   1 files changed, 22 insertions(+), 0 deletions(-)
>>
>> This needs to be backported to 4.3 and 4.4 as well
>>
>> diff --git a/xen/arch/x86/hvm/vpmu.c b/xen/arch/x86/hvm/vpmu.c
>> index 1df74c2..6d39680 100644
>> --- a/xen/arch/x86/hvm/vpmu.c
>> +++ b/xen/arch/x86/hvm/vpmu.c
>> @@ -247,10 +247,32 @@ void vpmu_initialise(struct vcpu *v)
>>       }
>>   }
>>   
>> +static void vpmu_clear_last(void *arg)
>> +{
>> +    struct vcpu *v = (struct vcpu *)arg;
>> +
>> +    if ( this_cpu(last_vcpu) == v )
>> +        this_cpu(last_vcpu) = NULL;
>> +}
>> +
>>   void vpmu_destroy(struct vcpu *v)
>>   {
>>       struct vpmu_struct *vpmu = vcpu_vpmu(v);
>>   
>> +    if ( vpmu_is_set(vpmu, VPMU_CONTEXT_ALLOCATED) )
>> +    {
>> +        /* Need to clear last_vcpu in case it points to v */
>> +        if ( vpmu->last_pcpu != smp_processor_id() )
>> +            on_selected_cpus(cpumask_of(vpmu->last_pcpu),
>> +                             vpmu_clear_last, (void *)v, 1);
>> +        else
>> +        {
>> +            local_irq_disable();
>> +            vpmu_clear_last((void *)v);
>> +            local_irq_enable();
>> +        }
>> +    }
>> +
>>       if ( vpmu->arch_vpmu_ops && vpmu->arch_vpmu_ops->arch_vpmu_destroy )
>>           vpmu->arch_vpmu_ops->arch_vpmu_destroy(v);
>>   }
>> -- 
>> 1.7.1
>>