Re: [Xen-devel] [PATCH] linux-2.6.18/x86_64: remove an inapplicable feature flag

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

>>> On 03.11.10 at 13:35, Jeremy Fitzhardinge <jeremy@xxxxxxxx> wrote:
> On 11/03/2010 05:13 AM, Jan Beulich wrote:
>>>>> On 03.11.10 at 09:59, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:
>>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>
>>>
>>> --- a/arch/x86_64/kernel/head-xen.S
>>> +++ b/arch/x86_64/kernel/head-xen.S
>>> @@ -206,6 +206,6 @@
>>>     ELFNOTE(Xen, XEN_ELFNOTE_ENTRY,          .quad,  startup_64)
>>>     ELFNOTE(Xen, XEN_ELFNOTE_HYPERCALL_PAGE, .quad,  hypercall_page)
>>>     ELFNOTE(Xen, XEN_ELFNOTE_L1_MFN_VALID,   .quad,  
>>> _PAGE_PRESENT,_PAGE_PRESENT)
>>> -   ELFNOTE(Xen, XEN_ELFNOTE_FEATURES,       .asciz, 
> "writable_page_tables|writable_descriptor_tables|auto_translated_physmap|pae_
> pgdir_above_4gb|supervisor_mode_kernel")
>>> +   ELFNOTE(Xen, XEN_ELFNOTE_FEATURES,       .asciz, 
> "writable_page_tables|writable_descriptor_tables|auto_translated_physmap|supe
> rvisor_mode_kernel")
>>>     ELFNOTE(Xen, XEN_ELFNOTE_LOADER,         .asciz, "generic")
>>>     ELFNOTE(Xen, XEN_ELFNOTE_SUSPEND_CANCEL, .long,  1)
>> If the flag was removed from the pv-ops 64-bit kernel too, we could
>> even start warning about inapplicable flags in hypervisor/tools.
>>
>> What puzzles me more though is that the pv-ops kernel requires
>> the writable_page_tables feature. Why is that?
> 
> It did in the very early days, but it hasn't used it since converting to
> PV MMU (couldn't, since it doesn't exist any more).  It lists
> "!writable_page_table", which I read as meaning "writable page tables
> not supported"; does it actually mean "must"?

Yes, it does (according to xen/include/public/elfnote.h).

Jan


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