Re: [Xen-devel] [PATCH] x86-64 linux: another adjustment to vmalloc fault handling

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> 17.02.06 12:05:13 >>>
>
>On 17 Feb 2006, at 10:38, Jan Beulich wrote:
>
>> Changeset 8847 improved things, but doesn't generally work. We namely 
>> experienced problems (when we originally tried the
>> same change) with accesses to machine_to_phys_mapping, which (in 
>> mfn_to_pfn) is specifically allowed to fault. Hence
>> there should not be attempts to fix up faults within the hypervisor 
>> range (as for any page table entries obtained there
>> no m2p translation exists for the guest, resulting in bogus physical 
>> addresses getting used for further fault
>> processing, frequently leading to nested faults).
>
>But machine_to_phys_mapping == 0xffff800000000000 while
>PAGE_OFFSET == HYPERVISOR_VIRT_END == 0xffff880000000000.
>
>So the patch doesn't really change anything, and 
>machine_to_phys_mapping lives below both PAGE_OFFSET and 
>HYPERVISOR_VIRT_END anyway.

Oh, I'm sorry, I mixed up TASK_SIZE64 and PAGE_OFFSET (we had used the former 
initially, because it's being done
similarly on i386). Between PAGE_OFFSET and HYPERVISOR_VIRT_END I just found 
using the latter here more correct, as
PAGE_OFFSET is not required to live at HYPERVISOR_VIRT_END, but that should 
always be the boundary for checking.

Jan

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