On 18/02/15 10:50, Andrew Cooper wrote:
> On 18/02/15 10:42, Juergen Gross wrote:
>>
>>>> /* Set up p2m_top to point to the domain-builder provided p2m
>>>> pages */
>>>> @@ -469,8 +473,10 @@ static pte_t *alloc_p2m_pmd(unsigned long addr,
>>>> pte_t *pte_pg)
>>>>
>>>> ptechk = lookup_address(vaddr, &level);
>>>> if (ptechk == pte_pg) {
>>>> + HYPERVISOR_shared_info->arch.p2m_generation++;
>>>> set_pmd(pmdp,
>>>> __pmd(__pa(pte_newpg[i]) | _KERNPG_TABLE));
>>>> + HYPERVISOR_shared_info->arch.p2m_generation++;
>>>
>>> Do these increments of p2m_generation need to be atomic?
>>
>> Hmm, they are done under lock. I don't think the compiler is allowed to
>> reorder the writes to p2m_generation across set_pmd().
>
> They do need smp_wmb() to guarantee that the increment is visible before
> the update occurs, just as the toolstack will need smp_rmb() to read.
smp_wmb() isn't good enough since you need the barrier even on non-smp
-- you need a wmb().
David
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