Re: [Xen-devel] [PATCH] x86/hap: fix race condition between ENABLE_LOGDIRTY and track_dirty_vram hypercall

[Tim Deegan <tim@xxxxxxx>]

At 16:02 +0900 on 29 Nov (1354204941), Kouya Shimura wrote:
> I'm not sure why paging_lock() is used partially in hap_XXX_vram_tracking
> functions. Thus, this patch introduces a new lock.
> It would be better to use paging_lock() instead of the new lock
> since shadow paging mode (not HAP mode) uses paging_lock to avoid
> this race condition.

I think you're right - it would be better to use the paging_lock. 

Cc'ing Robert Phillips, who's got a big patch outstanding that touches
the locking in this code.  I think the right thing to do is make sure
his patch fixes the issue and the backport just the locking parts of it
to older trees.

Robert, in your patch you do wrap this all in the paging_lock, but then
unlock to call various enable and disable routines.  Is there a version
of this reace condition there, where some other CPU might call
LOG_DIRTY_ENABLE while you've temporarily dropped the lock?

Cheers,

Tim.

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