Re: [PATCH v4 RFC 6/6] x86/MSI: properly track guest masking requests

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 25/06/15 09:04, Jan Beulich wrote:
>>>> On 24.06.15 at 19:24, <andrew.cooper3@citrix.com> wrote:
>> On 22/06/15 15:51, Jan Beulich wrote:
>>> --- a/xen/arch/x86/msi.c
>>> +++ b/xen/arch/x86/msi.c
>>> @@ -1308,6 +1308,39 @@ printk("%04x:%02x:%02x.%u: MSI-X %03x:%u
>>>          return 1;
>>>      }
>>>  
>>> +    entry = find_msi_entry(pdev, -1, PCI_CAP_ID_MSI);
>>> +    if ( entry && entry->msi_attrib.maskbit )
>>> +    {
>>> +        uint16_t cntl;
>>> +        uint32_t unused;
>>> +
>>> +        pos = entry->msi_attrib.pos;
>>> +        if ( reg < pos || reg >= entry->msi.mpos + 8 )
>>> +            return 0;
>>> +printk("%04x:%02x:%02x.%u: MSI %03x:%u->%04x\n", seg, bus, slot, func, reg, size, *data);//temp
>>> +
>>> +        if ( reg == msi_control_reg(pos) )
>>> +            return size == 2 ? 1 : -EACCES;
>>> +        if ( reg < entry->msi.mpos || reg >= entry->msi.mpos + 4 || size != 4 )
>>> +            return -EACCES;
>> Can we avoid using EACCES to avoid confusing it with a mismatched tools
>> version?
> What other suitable error code would you see here? I'm not sure
> we want this error code to be reserved for exactly one purpose,
> the more that here we're on a path that will never has this error
> code returned to the guest (and even less so via a domctl/sysctl,
> which would be the primary mismatched-tools-version candidates).

If there is no chance that we will end up back on a domctl/sysctl error
path then its use is fine.

~Andrew