Re: [Xen-devel] [PATCH] xen/arm: p2m: Restrict preemption check in apply_p2m_changes

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Konrad,

On 05/05/15 16:50, Konrad Rzeszutek Wilk wrote:
>> ---
>>  xen/arch/arm/p2m.c | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
>> index 65efa94..59dd23a 100644
>> --- a/xen/arch/arm/p2m.c
>> +++ b/xen/arch/arm/p2m.c
>> @@ -948,6 +948,7 @@ static int apply_p2m_changes(struct domain *d,
>>      const unsigned long sgfn = paddr_to_pfn(start_gpaddr),
>>                          egfn = paddr_to_pfn(end_gpaddr);
>>      const unsigned int preempt_count_limit = (op == MEMACCESS) ? 1 : 0x2000;
>> +    const bool_t preempt = !is_idle_vcpu(current);
>>      bool_t flush = false;
>>      bool_t flush_pt;
>>  
>> @@ -980,7 +981,8 @@ static int apply_p2m_changes(struct domain *d,
>>           * always make at least one pass as long as preempt_count_limit is
>>           * initialized with a value >= 1.
>>           */
>> -        if ( count >= preempt_count_limit && hypercall_preempt_check() )
>> +        if ( preempt && count >= preempt_count_limit
>> +             && hypercall_preempt_check() )
> 
> Could you  use the softirq_pending() check to deal when there are no domains?

apply_p2m_changes will only be called with no current domain (i.e idle
vcpu) during DOM0 construction.

If we check softirq_pending for this case, you will Xen will fail to
build DOM0 but the preemption is not supported.

I suspect this is the same on x86.

Regards,

-- 
Julien Grall

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