Am 02.11.2010 07:52, Sheng Yang wrote:
> On Monday 01 November 2010 19:41:21 Jan Kiszka wrote:
>> Hi Sheng,
>>
>> I'm not claiming to understand the details, but this looks like use
>> (dereference of pte via dma_pte_addr) after release (free_pgtable_page
>> of dmar_domain->pgd aka pte) to me:
>>
>> static int intel_iommu_attach_device(struct iommu_domain *domain,
>> struct device *dev)
>> {
>> [...]
>> pte = dmar_domain->pgd;
>> if (dma_pte_present(pte)) {
>> free_pgtable_page(dmar_domain->pgd);
>> dmar_domain->pgd = (struct dma_pte *)
>> phys_to_virt(dma_pte_addr(pte));
>> }
>>
>> At least it crashes here right on pte->val access. Swap both lines?
>
> I think code is right.
>
> The comment above indicate the case: the code want to decrease the level of page
> table. Mostly it is a 4 level page table, and the code would turn it into 3 levels
> pagetable. What the code did is just get the first entry of the old pagetable level
> 4, then free the level 4 pagetable's page, and make the pagetable to a level 3
> pagetable.
>
> Seems it make no sense to swap the lines...
It fixes the crash here, and I'm convinced the current code is wrong.
See the patch I've just sent out.
Jan
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