Re: [Xen-devel] [PATCH] x86: consider modules when cutting off memory

[Keir Fraser <keir.xen@xxxxxxxxx>]

On 18/11/2013 04:11, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:

>>>> On 18.11.13 at 12:32, Keir Fraser <keir.xen@xxxxxxxxx> wrote:
>> On 18/11/2013 00:37, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:
>> 
>>> The code in question runs after module ranges got already removed from
>>> the E820 table, so when determining the new maximum page/PDX we need to
>>> explicitly take them into account.
>>> 
>>> Furthermore we need to round up the ending addresses here, in order to
>>> fully cover eventual partial trailing pages.
>> 
>> Is rounding up the right thing to do? We round down in find_max_pfn()?
> 
> Yes, it is - we're trying to determine a new max_page/max_pdx
> here, so we should include the trailing part of a partial page. This
> is particularly necessary for the modules, as otherwise the last
> few bytes of a module may end up being in memory not satisfying
> mfn_valid().
> 
> If anything, we'd need to round down after the E820 loop, and
> round up after the modules one. But I don't think the two max_p*
> being one too big here would matter much, so uniformly rounding
> up seems sufficient.

Okay makes sense.

Acked-by: Keir Fraser <keir@xxxxxxx>

> Jan
> 
>>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>>> 
>>> --- a/xen/arch/x86/setup.c
>>> +++ b/xen/arch/x86/setup.c
>>> @@ -1013,9 +1013,17 @@ void __init __start_xen(unsigned long mb
>>>                      ASSERT(j);
>>>                  }
>>>                  map_e = boot_e820.map[j].addr + boot_e820.map[j].size;
>>> -                if ( (map_e >> PAGE_SHIFT) < max_page )
>>> +                for ( j = 0; j < mbi->mods_count; ++j )
>>>                  {
>>> -                    max_page = map_e >> PAGE_SHIFT;
>>> +                    uint64_t end = pfn_to_paddr(mod[j].mod_start) +
>>> +                                   mod[j].mod_end;
>>> +
>>> +                    if ( map_e < end )
>>> +                        map_e = end;
>>> +                }
>>> +                if ( PFN_UP(map_e) < max_page )
>>> +                {
>>> +                    max_page = PFN_UP(map_e);
>>>                      max_pdx = pfn_to_pdx(max_page - 1) + 1;
>>>                  }
>>>                  printk(XENLOG_WARNING "Ignoring inaccessible memory range"
>>> 
>>> 
>>> 
> 
> 
> 



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