* [PATCH] linux-2.6.18/x86_64: remove an inapplicable feature flag
@ 2010-11-03 8:59 Jan Beulich
2010-11-03 9:13 ` Jan Beulich
0 siblings, 1 reply; 5+ messages in thread
From: Jan Beulich @ 2010-11-03 8:59 UTC (permalink / raw)
To: xen-devel@lists.xensource.com
[-- Attachment #1: Type: text/plain, Size: 803 bytes --]
Signed-off-by: Jan Beulich <jbeulich@novell.com>
--- 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|supervisor_mode_kernel")
ELFNOTE(Xen, XEN_ELFNOTE_LOADER, .asciz, "generic")
ELFNOTE(Xen, XEN_ELFNOTE_SUSPEND_CANCEL, .long, 1)
[-- Attachment #2: xen-x86_64-no-pae-above-4gb.patch --]
[-- Type: text/plain, Size: 853 bytes --]
Subject: x86_64: remove an inapplicable feature flag
Signed-off-by: Jan Beulich <jbeulich@novell.com>
--- 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|supervisor_mode_kernel")
ELFNOTE(Xen, XEN_ELFNOTE_LOADER, .asciz, "generic")
ELFNOTE(Xen, XEN_ELFNOTE_SUSPEND_CANCEL, .long, 1)
[-- Attachment #3: Type: text/plain, Size: 138 bytes --]
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^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] linux-2.6.18/x86_64: remove an inapplicable feature flag
2010-11-03 8:59 [PATCH] linux-2.6.18/x86_64: remove an inapplicable feature flag Jan Beulich
@ 2010-11-03 9:13 ` Jan Beulich
2010-11-03 12:35 ` Jeremy Fitzhardinge
0 siblings, 1 reply; 5+ messages in thread
From: Jan Beulich @ 2010-11-03 9:13 UTC (permalink / raw)
To: Jeremy Fitzhardinge; +Cc: xen-devel@lists.xensource.com
>>> On 03.11.10 at 09:59, "Jan Beulich" <JBeulich@novell.com> wrote:
> Signed-off-by: Jan Beulich <jbeulich@novell.com>
>
> --- 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|supervisor_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? And assuming it
supports it at all (which seems questionable given that it unlikely
was ever tested), why would it not also indicate support for
writable_descriptor_tables and auto_translated_physmap?
Jan
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] linux-2.6.18/x86_64: remove an inapplicable feature flag
2010-11-03 9:13 ` Jan Beulich
@ 2010-11-03 12:35 ` Jeremy Fitzhardinge
2010-11-03 14:04 ` Jan Beulich
0 siblings, 1 reply; 5+ messages in thread
From: Jeremy Fitzhardinge @ 2010-11-03 12:35 UTC (permalink / raw)
To: Jan Beulich; +Cc: xen-devel@lists.xensource.com
On 11/03/2010 05:13 AM, Jan Beulich wrote:
>>>> On 03.11.10 at 09:59, "Jan Beulich" <JBeulich@novell.com> wrote:
>> Signed-off-by: Jan Beulich <jbeulich@novell.com>
>>
>> --- 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|supervisor_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"?
J
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] linux-2.6.18/x86_64: remove an inapplicable feature flag
2010-11-03 12:35 ` Jeremy Fitzhardinge
@ 2010-11-03 14:04 ` Jan Beulich
2010-11-03 14:50 ` Ian Campbell
0 siblings, 1 reply; 5+ messages in thread
From: Jan Beulich @ 2010-11-03 14:04 UTC (permalink / raw)
To: Jeremy Fitzhardinge; +Cc: xen-devel@lists.xensource.com
>>> On 03.11.10 at 13:35, Jeremy Fitzhardinge <jeremy@goop.org> wrote:
> On 11/03/2010 05:13 AM, Jan Beulich wrote:
>>>>> On 03.11.10 at 09:59, "Jan Beulich" <JBeulich@novell.com> wrote:
>>> Signed-off-by: Jan Beulich <jbeulich@novell.com>
>>>
>>> --- 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
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] linux-2.6.18/x86_64: remove an inapplicable feature flag
2010-11-03 14:04 ` Jan Beulich
@ 2010-11-03 14:50 ` Ian Campbell
0 siblings, 0 replies; 5+ messages in thread
From: Ian Campbell @ 2010-11-03 14:50 UTC (permalink / raw)
To: Jan Beulich; +Cc: Jeremy Fitzhardinge, xen-devel@lists.xensource.com
On Wed, 2010-11-03 at 14:04 +0000, Jan Beulich wrote:
> >>> On 03.11.10 at 13:35, Jeremy Fitzhardinge <jeremy@goop.org> wrote:
> > On 11/03/2010 05:13 AM, Jan Beulich wrote:
> >>>>> On 03.11.10 at 09:59, "Jan Beulich" <JBeulich@novell.com> wrote:
> >>> Signed-off-by: Jan Beulich <jbeulich@novell.com>
> >>>
> >>> --- 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).
The selection of ! for this meaning was very ill-conceived! I don't know
what I was thinking...
I think it is correct to remove this flag. The pvops kernel has no
support for running in a mode where page tables are not read-only, which
is not to be confused with the trap-n-emulate type of writeable page
table update which it does use.
Ian.
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2010-11-03 14:50 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz follow: Atom feed
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2010-11-03 8:59 [PATCH] linux-2.6.18/x86_64: remove an inapplicable feature flag Jan Beulich
2010-11-03 9:13 ` Jan Beulich
2010-11-03 12:35 ` Jeremy Fitzhardinge
2010-11-03 14:04 ` Jan Beulich
2010-11-03 14:50 ` Ian Campbell
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