Re: [Xen-devel] page fault handling in Xen

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 8 Oct 2005, at 23:39, Jonathan M. McCune wrote:

> We're curious about page fault handling in Xen-devel.  In particular, 
> during kernel boot-up, the kernel tests if the CPU "honours the WP 
> bit". This causes a page fault with error code 3 (expected behavior).  
> Does Xen still make a copy of the execution stack frame on the guest 
> OS stack, as specified in the original "Xen and the Art of 
> Virtualization" paper?  There is a footnote here that suggests that 
> using a pre-agreed shared memory location might be a better option.  
> Has this change been implemented?
> After the WP-test page fault is taken, what is supposed to happen from 
> Xen's perspective on the return from the page fault handler?  In 
> normal linux, the exception handler changes its own return address 
> (i.e., modifies the EIP register) to be the "fixup" address.  Does 
> this still happen with XenoLinux, or does the hypervisor get involved?
Everything works as on native, pretty much, except that the page-fault 
stack frame is extended by one word to contain the faulting linear 
address (because the guest cannot directly access %cr2).
 -- Keir


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