Re: [Xen-devel] [PATCH 5/6] x86: enable multi-vector MSI

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 23.04.13 at 02:55, Suravee Suthikulanit <suravee.suthikulpanit@xxxxxxx>
wrote:
> On 4/19/2013 5:59 AM, Jan Beulich wrote:
>> --- a/xen/arch/x86/msi.c
>> +++ b/xen/arch/x86/msi.c
>> @@ -238,6 +238,11 @@ static int write_msi_msg(struct msi_desc
>>           u8 bus = dev->bus;
>>           u8 slot = PCI_SLOT(dev->devfn);
>>           u8 func = PCI_FUNC(dev->devfn);
>> +        int nr = entry->msi_attrib.entry_nr;
>> +
>> +        ASSERT((msg->data & (entry[-nr].msi.nvec - 1)) == nr);
>> +        if ( nr )
>> +            return 0;
> 
> This logic seems incorrect.  Do you meant to write --nr?

No, this indeed has to be -nr (i.e. the "master" entry, which is the
first on in the array.

> This causes assertion here.  Also, investigation showing the
> value of nr is 0 here.

nr being 0 here is perfectly fine, meaning this is the first ("master")
entry of a multi-vector device (it can't be a single-vector one, as in
that case entry[0].msi.nvec == 1, i.e. the & yields zero regardless
of msg->data).

And the assertion should hold, due to

    *data = (msg->data & ~(INTREMAP_ENTRIES - 1)) | offset;

in update_intremap_entry_from_msi_msg(), and
alloc_intremap_entry() returning only aligned blocks.

So the question isn't just what value nr there has, but also what
the other involved values are.

Jan


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