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

["Jan Beulich" <JBeulich@suse.com>]

>>> 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).

It's also odd that you ask for this here, when patch 2 has a use
of this error code too.

Jan