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Re: [Xen-devel] Re: [PATCH] Xen Guest Kexec

On 2 Mar 2006, at 16:36, Gerd Hoffmann wrote:

Looks like your new pagetables have a writable mapping of MFN 18c95,
which is the new page directory. i.e., the new p.t. set is not self

They where indeed.  Wrong usage of pte_wrprotect() :-/
Next question: Is there some way to _clear_ the trap table?

Hehe. The interface wasn't so much designed with this in mind, but it can be done. Pass in an array of 256 trap_info structs, where the i'th struct contains:
  vector=i, flags=0, cs=0, addr=1

Note the address must be non-zero, as that otherwise marks the end of the list! You can put whatever non-zero value you like in that field -- it really doesn't matter. In fact you need to pass a list of *257* trap_info structs, the last of which has addr==0. :-)

The critical thing that disables the trap is flags==0: that sets the 'dpl' for the 'trap gate' to zero so it effectively is unusable.

 -- Keir

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