[Xen-devel] Re: A race condition in xenlinux exit_mmap

[hanzhu <hanzhu@xxxxxxxxxxx>]

Hi, Keir,
Why not just reuse VM_FOREIGN(blktap uses this flag to represent foreign 
mapped vma) flag to unmap the foreign mapped pages before call 
arch_exit_mmap? This could be a simple alternative.
_______________________________________________________
Best Regards,
hanzhu



Keir Fraser дµÀ:
> On 1 Aug 2006, at 10:21, Li, Xin B wrote:
>
> > 2 possible solutions are:
> > 1) call arch_exit_mmap after unmap_vmas.
> > 2) unmap foreign mapped pages before calling arch_exit_mmap, and then we
> > can do the normal cleanup jobs.
> A longer term plan is to add an explicit flag to PTEs that are foreign 
> mappings (and so are not refcounted). However, I think the easiest 
> solution for now is to add a flag to mmu_context structure indicating 
> whether this mm has ever had any foreign mappings (so you would set it 
> in direct_remap_pfn_range()). If it has then we do not call mm_unpin() 
> from _arch_exit_mmap() -- doing so is only an optimisation which we 
> can simply not do for the very small number of mm's that have foreign 
> mappings.
> Do you mind creating a patch to do this? I can send you more details 
> if you like.
>  -- Keir
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