RE: [Xen-devel] Switching from writeable pagetable to shadow log-dirtyat runtime

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

> When we switch from writeable pagetable to shadow log-dirty 
> mode at runtime, there are some PTEs with write-protected; 
> once we do ptwr_flush(), we write-protect back the page 
> table. If we simply consult the guest page tables when 
> building the shadow page tables, then we also copy the write 
> protection to the shadow pages tables. Since the shadow code 
> does not have the logic for the writeable page table, the 
> guest kernel, for exmaple, can see write-protected page 
> table, resulting a panic. We are experiencing the problem 
> with PAE log-dirty mode (that we are working on now).

We should certainly be doing a ptwr_flush() before switching page table
modes.

My recollection is that domain_pause in shadow_enable would cause a
sync_pagetable_state, but that code has changed a lot since I wrote it.

Ian

> So I think the current state in the writeable page should be 
> flushed and adjusted (in audit, for example, make the 
> write-protected pages back to
> writeable) before we switch to shadow mode. Given the fact 
> that we can switch writeable pagetable to shadow log-dirty at 
> runtime for the plain 32-bit, I'm wondering where we are 
> doing that kind of thing.
> 
> Jun
> ---
> Intel Open Source Technology Center 
> 
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