linux-kernel - Re: Crash in intel_iommu_assign

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Date:	Tue, 2 Nov 2010 14:52:19 +0800
From:	Sheng Yang <sheng@...ux.intel.com>
To:	Jan Kiszka <jan.kiszka@....de>
Cc:	kvm <kvm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Crash in intel_iommu_assign_device

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...

--
regards
Yang, Sheng

> 
> Jan
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