[Xen-devel] RE: [PATCH] X server crashes Xen on xeno-unstable.bk

["Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>]

> Starting an X server on xeno-unstable.bk causes Xen to crash with
> a page fault generated in Xen. It turns out that the fault is
> generated by put_page_from_l1e().
> 
> The culprit is the following dereference:
> 
>      struct domain   *e = page->u.inuse.domain;
> 
> Where the value of page is undefined if the condition
> 
>      if ( !(l1v & _PAGE_PRESENT) || !pfn_is_ram(pfn) )
> 
> does hold. Unfortunately, this condition is checked after the 
> dereference.

Interesting. I'm guessing the reason we haven't seen this is that we
don't build on FC3. The newer version of gcc has obviously spotted the
opportunity to hoist the load.

I'll checkin the fix.

Thanks,
Ian


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