Re: [PATCH] x86/iommu: account for necessary allocations when calculating Dom0's initial allocation size

["Jan Beulich" <JBeulich@novell.com>]

>>> On 14.12.10 at 10:28, Keir Fraser <keir@xen.org> wrote:
> Thank Jan. I'm not really sure about putting your earlier patch into 4.0.2,
> so can I put only this patch in for 4.0.2, replacing max_pdx with max_page?

Yes, that would be the correct equivalent without that other patch.

But it is clear that without the other one a system may not even
boot if the holes are large enough - but that's the case in plain
4.0.0 too, i.e. not a regression.

Jan

> On 14/12/2010 09:03, "Jan Beulich" <JBeulich@novell.com> wrote:
> 
>> As of c/s 21812:e382656e4dcc, IOMMU related allocations for Dom0
>> happen only after it got all of its memory allocated, and hence the
>> reserve (mainly for setting up its swiotlb) may get exhausted without
>> accounting for the necessary allocations up front.
>> 
>> While not precise, the estimate has been found to be within a couple
>> of pages for the systems it got tested on.
>> 
>> For the calculation to be reasonably correct, this depends on the
>> patch titled "x86/iommu: don't map RAM holes above 4G" sent out
>> yesterday.
>> 
>> Signed-off-by: Jan Beulich <jbeulich@novell.com>
>> 
>> --- a/xen/arch/x86/domain_build.c
>> +++ b/xen/arch/x86/domain_build.c
>> @@ -191,6 +191,15 @@ static unsigned long __init compute_dom0
>>      if ( is_pv_32on64_domain(d) )
>>          avail -= opt_dom0_max_vcpus - 1;
>>  
>> +    /* Reserve memory for iommu_dom0_init() (rough estimate). */
>> +    if ( iommu_enabled )
>> +    {
>> +        unsigned int s;
>> +
>> +        for ( s = 9; s < BITS_PER_LONG; s += 9 )
>> +            avail -= max_pdx >> s;
>> +    }
>> +
>>      /*
>>       * If domain 0 allocation isn't specified, reserve 1/16th of available
>>       * memory for things like DMA buffers. This reservation is clamped to
>> 
>> 
>> 
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