Re: [PATCH 7/9] vpci/header: program p2m with guest BAR view

[Oleksandr Andrushchenko <Oleksandr_Andrushchenko@xxxxxxxx>]

On 09.09.21 11:26, Jan Beulich wrote:
> On 09.09.2021 08:13, Oleksandr Andrushchenko wrote:
>> On 06.09.21 17:51, Jan Beulich wrote:
>>> On 03.09.2021 12:08, Oleksandr Andrushchenko wrote:
>>>> @@ -37,12 +41,28 @@ static int map_range(unsigned long s, unsigned long e, 
>>>> void *data,
>>>>                         unsigned long *c)
>>>>    {
>>>>        const struct map_data *map = data;
>>>> +    gfn_t start_gfn;
>>>>        int rc;
>>>>    
>>>>        for ( ; ; )
>>>>        {
>>>>            unsigned long size = e - s + 1;
>>>>    
>>>> +        /*
>>>> +         * Any BAR may have holes in its memory we want to map, e.g.
>>>> +         * we don't want to map MSI regions which may be a part of that 
>>>> BAR,
>>>> +         * e.g. when a single BAR is used for both MMIO and MSI.
>>>> +         * In this case MSI regions are subtracted from the mapping, but
>>>> +         * map->start_gfn still points to the very beginning of the BAR.
>>>> +         * So if there is a hole present then we need to adjust start_gfn
>>>> +         * to reflect the fact of that substraction.
>>>> +         */
>>>> +        start_gfn = gfn_add(map->start_gfn, s - mfn_x(map->start_mfn));
>>> I may be missing something, but don't you need to adjust "size" then
>>> as well?
>> No, as range sets get consumed we have e and s updated accordingly,
>> so each time size represents the right value.
> It feels like something's wrong with the rangeset construction then:
> Either it represents _all_ holes (including degenerate ones at the
> start of end of a range), or none of them.

The resulting range set only has the MMIOs in it. While constructing the range 
set

we cut off MSI-X out of it (make holes). But finally it only has the ranges 
that we

need to map/unmap.

>
> Jan
>
Thank you,

Oleksandr