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On 07.01.13 at 13:52, Daniel Kiper [off-list ref] wrote:

On Mon, Jan 07, 2013 at 09:48:20AM +0000, Jan Beulich wrote:

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On 04.01.13 at 18:25, Daniel Kiper [off-list ref] wrote:

Right, so where is virtual mapping of control page established?
I could not find relevant code in SLES kernel which does that.

In the hypervisor (xen/arch/x86/machine_kexec.c:machine_kexec_load()).
xen/arch/x86/machine_kexec.c:machine_kexec() then simply uses
image->page_list[1].

This (xen/arch/x86/machine_kexec.c:machine_kexec_load()) maps relevant
page (allocated earlier by dom0) in hypervisor fixmap area. However,
it does not make relevant mapping in transition page table which
leads to crash when %cr3 is switched from Xen page table to
transition page table.

That indeed could explain _random_ failures - the fixmap entries
get created with _PAGE_GLOBAL set, i.e. don't get flushed with
the CR3 write unless CR4.PGE is clear.

And I don't see how your allocation of intermediate page tables
would help: You wouldn't know where the mapping of the control
page lives until you're actually in the early relocate_kernel code.
Or was it that what distinguishes your cloned code from the
native original?

Jan