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


  • To: Oleksandr Andrushchenko <Oleksandr_Andrushchenko@xxxxxxxx>, Oleksandr Andrushchenko <andr2000@xxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Thu, 9 Sep 2021 10:26:58 +0200
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  • Cc: "julien@xxxxxxx" <julien@xxxxxxx>, "sstabellini@xxxxxxxxxx" <sstabellini@xxxxxxxxxx>, Oleksandr Tyshchenko <Oleksandr_Tyshchenko@xxxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Artem Mygaiev <Artem_Mygaiev@xxxxxxxx>, "roger.pau@xxxxxxxxxx" <roger.pau@xxxxxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Rahul Singh <rahul.singh@xxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Thu, 09 Sep 2021 08:27:07 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

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.

Jan




 


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