page fault handling in Xen

["Jonathan M. McCune" <jonmccune@cmu.edu>]

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Hello,

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?

Thanks,
-Jon


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