Re: [Xen-devel] Failure in update_l1e()

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

> hi,
> 
> I am seeing occasional failures of cmpxchg_user() in update_l1e().
> According to the the comments in the source, this is due to a page fault
> caused by the update.
> 
> The error looks like this:
> 
> (XEN) DOM5: (file=memory.c, line=670) Failed to update 08fe6065 ->
> 08fe6465: saw 08fe6065
> DOM5: Failed update VA mapping: 000bffff, 08fe6465, 00000002
> 
> The odd value is due to a special use of one of the AVL bits for my own
> purposes.
> 
> This only happens when page_nr is 000bffff for some reason.
> 
> Any ideas what may be going wrong here?

Most likely the page that you are trying to modify is mapped
read-only.

Any PTE linear address passed to update_va_mapping() /must/ be
writeable, or teh update will fail.

 -- Keir


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