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Re: [Xen-devel] grant table interface addition?

from [Jan Beulich]

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To:	"Keir Fraser" <keir.fraser@xxxxxxxxxxxxx>
Subject:	Re: [Xen-devel] grant table interface addition?
From:	"Jan Beulich" <jbeulich@xxxxxxxxxx>
Date:	Mon, 03 Nov 2008 13:28:48 +0000
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>>> Keir Fraser <keir.fraser@xxxxxxxxxxxxx> 03.11.08 13:55 >>>
>On 3/11/08 12:13, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:
>
>> While looking in more detail into how all this fits together, I realized that
>> there appears to be a race condition in blktap: Since fast_flush_area()
>> and dispatch_rw_block_io() call create_lookup_pte_addr() without holding
>> mm->mmap_sem, there's nothing preventing the just verified (or
>> created) page table structures to go away again before
>> HYPERVISOR_grant_table_op() is able to finish (or even begin) its job.
>> Am I missing something here?
>
>So, for example, it could be munmap()ed under those functions' feet? Or the
>process could die? Looks like you could be right, although I've never looked
>closely at the blktap kernel driver.

Process death is probably not a concern, but munmap() of the region in
question or (potentially, maybe not in current kernels) even a nearby one
is.

Jan


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