Re: [Xen-devel] [PATCH v4 RFC 2/6] x86/MSI-X: track host and guest maskâall requests separately

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 24.06.15 at 19:15, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 22/06/15 15:47, Jan Beulich wrote:
>> Host uses of the bits will be added subsequently, and must not be
>> overridden by guests (including Dom0, namely when acting on behalf of
>> a guest).
>>
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>>
>> --- a/xen/arch/x86/msi.c
>> +++ b/xen/arch/x86/msi.c
>> @@ -846,6 +846,12 @@ static int msix_capability_init(struct p
>>  
>>      if ( !msix->used_entries )
>>      {
>> +        msix->host_maskall = 0;
>> +        if ( !msix->guest_maskall )
>> +            control &= ~PCI_MSIX_FLAGS_MASKALL;
>> +        else
>> +            control |= PCI_MSIX_FLAGS_MASKALL;
> 
> Is the guest (or hardware) in a position to influence guest_maskall at
> this point?  I am not sure that it is.

Of course - via the cfg write intercept (i.e. the hunk immediately
following this one).

Jan


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