[Xen-devel] kexec design issues

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

As I became aware of only now (by way of a bug report), Linux side kexec
changes on i386 silently broke assumptions in the kexec hypercall interface.
Therefore I'd like to get an understanding on what the general perspective
on the following problems is:

1) machine_kexec_load() silently assumes that page_list[] has alternating
(and paired) physical/virtual entries. This is no longer valid with 2.6.27, and
while the immediate fix is to re-arrange the list entries so that the newly
added entry would end up after all pairs (in 2.6.29 an extra gap will need
to be added), this points out that the interface definition itself is really
flawed.

2) KEXEC_XEN_NO_PAGES is set to the apparently arbitrary value of 17.
While a build error would clearly show any incompatible Linux side change
in this case, it still seems bogus to hard-code this Linux defined value into
the hypercall interface.

3) machine_kexec_load() blindly iterates over all page_list[] entries,
regardless of whether any of them is zero, and hence establishes
(currently on 32-bit only) numerous bogus page table entries mapping
mfn 0.

Thanks for any comments,
Jan


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