Re: [PATCH v2 8/8] vpci/msix: Add function to clean MSIX resources

["Chen, Jiqian" <Jiqian.Chen@xxxxxxx>]

On 2025/4/17 15:34, Jan Beulich wrote:
> On 09.04.2025 08:45, Jiqian Chen wrote:
>> --- a/xen/arch/x86/hvm/intercept.c
>> +++ b/xen/arch/x86/hvm/intercept.c
>> @@ -276,6 +276,50 @@ void register_mmio_handler(struct domain *d,
>>      handler->mmio.ops = ops;
>>  }
>>  
>> +void unregister_mmio_handler(struct domain *d,
>> +                             const struct hvm_mmio_ops *ops)
>> +{
>> +    unsigned int i, count = d->arch.hvm.io_handler_count;
>> +
>> +    ASSERT(d->arch.hvm.io_handler);
>> +
>> +    if ( !count )
>> +        return;
>> +
>> +    for ( i = 0; i < count; i++ )
>> +        if ( d->arch.hvm.io_handler[i].type == IOREQ_TYPE_COPY &&
>> +             d->arch.hvm.io_handler[i].mmio.ops == ops )
>> +            break;
>> +
>> +    if ( i == count )
>> +        return;
>> +
>> +    for ( ; i < count - 1; i++ )
>> +    {
>> +        struct hvm_io_handler *curr = &d->arch.hvm.io_handler[i];
>> +        struct hvm_io_handler *next = &d->arch.hvm.io_handler[i + 1];
>> +
>> +        curr->type = next->type;
>> +        curr->ops = next->ops;
>> +        if ( next->type == IOREQ_TYPE_COPY )
>> +        {
>> +            curr->portio.port = 0;
>> +            curr->portio.size = 0;
>> +            curr->portio.action = 0;
>> +            curr->mmio.ops = next->mmio.ops;
>> +        }
>> +        else
>> +        {
>> +            curr->mmio.ops = 0;
>> +            curr->portio.port = next->portio.port;
>> +            curr->portio.size = next->portio.size;
>> +            curr->portio.action = next->portio.action;
>> +        }
>> +    }
>> +
>> +    d->arch.hvm.io_handler_count--;
>> +}
> 
> To add on what Roger said: This is inherently non-atomic, so the domain
> would need pausing to do such removal in a race-free way. Hence why we
> deliberately didn't have such a function so far, aiui. (The removal may
> be safe in the specific case you use it helow, but there's nothing here
> preventing it from being used elsewhere, without paying attention to
> the raciness.)
Make sense, thanks for your detailed inputs.
I will delete this part in next version.

> 
> Jan

-- 
Best regards,
Jiqian Chen.