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From: "Jan Beulich" <jbeulich@novell.com>
To: "Jeremy Fitzhardinge" <jeremy@goop.org>
Cc: <virtualization@lists.osdl.org>, <xen-devel@lists.xensource.com>,
	"Andi Kleen" <ak@muc.de>, "Andrew Morton" <akpm@osdl.org>,
	"Chris Wright" <chrisw@sous-sol.org>,
	<linux-kernel@vger.kernel.org>, "Dan Hecht" <dhecht@vmware.com>
Subject: [Xen-devel] Re: [patch 05/21] Xen-paravirt: paravirt_ops: allocate a fixmap slot
Date: Wed, 14 Feb 2007 08:37:26 +0000	[thread overview]
Message-ID: <45D2D856.76E4.0078.0@novell.com> (raw)
In-Reply-To: <45D26797.5090600@goop.org>

>>> Jeremy Fitzhardinge <jeremy@goop.org> 14.02.07 02:36 >>>
>Dan Hecht wrote:
>> Why doesn't Xen allocate the shared_info page from the pseudo-physical
>> space?  Doesn't it already have to steal pages from the
>> pseudo-physical space for e.g. initial page tables, console, etc?  Why
>> not do the same for shared_info, and then you don't need a reserve the
>> fixmap slot.
>
>Unlike the pagetable pages or the console page, the shared info page
>doesn't have a pseudo-physical address, so in order to map it we need to
>directly construct a pte containing the mfn for that page.  Inserting
>this mapping into the fixmap space seems like the easiest way to do
>this.  It's not like a fixmap slot costs anything.

Otoh there are many fixmap slots not used under Xen, perhaps it would
be possible to use one of those... One slot certainly doesn't cost a lot,
but many (like the IO-APIC group) may already matter, especially on
PAE systems with lots of memory). Consequently, if these can't be
squeezed out as needed, re-using would seem more appropriate than
adding.
(I would certainly favor [conditionally] removing them, but can't easily
see how to do this under CONFIG_PARAVIRT. Background being that
we've already been hit by those [namely the LAPIC one] remaining
present, hence the build not being able to detect that accesses to the
LAPIC page can't work. While no such access was ever left in the base
kernel, modules are more susceptible to this, and in our case it was
the [native, i.e. pre-xenoprof] oprofile driver that had been forgotten
to be disabled.)

Jan

  parent reply	other threads:[~2007-02-14  8:36 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20070213221729.772002682@goop.org>
     [not found] ` <20070213221829.929261125@goop.org>
2007-02-13 22:39   ` [patch 06/21] Xen-paravirt: remove ctor for pgd cache Zachary Amsden
     [not found] ` <20070213221830.466651996@goop.org>
2007-02-13 22:45   ` [patch 13/21] Xen-paravirt: Add nosegneg capability to the vsyscall page notes Zachary Amsden
2007-02-13 22:49     ` Jeremy Fitzhardinge
2007-02-13 22:54       ` Zachary Amsden
2007-02-13 23:13         ` Jeremy Fitzhardinge
2007-02-14  5:38     ` [Xen-devel] " Rusty Russell
     [not found] ` <20070213221830.542511707@goop.org>
2007-02-13 22:53   ` [patch 14/21] Xen-paravirt: Add XEN config options and disable unsupported config options Dan Hecht
2007-02-13 23:29     ` Jeremy Fitzhardinge
2007-02-13 23:58       ` [Xen-devel] " Zachary Amsden
2007-02-13 23:58       ` Dan Hecht
     [not found] ` <20070213221830.238235953@goop.org>
2007-02-14  1:06   ` [patch 10/21] Xen-paravirt: Name: dont export paravirt_ops structure, do individual functions Zachary Amsden
2007-02-14  1:16     ` Jeremy Fitzhardinge
2007-02-14  1:18       ` Zachary Amsden
2007-02-14  1:37         ` Jeremy Fitzhardinge
2007-02-14  1:43           ` Zachary Amsden
2007-02-14  1:44             ` Jeremy Fitzhardinge
2007-02-14  5:51     ` Rusty Russell
2007-02-14 19:36     ` Christoph Hellwig
     [not found] ` <20070213221829.845132535@goop.org>
2007-02-14  1:23   ` [patch 05/21] Xen-paravirt: paravirt_ops: allocate a fixmap slot Dan Hecht
2007-02-14  1:36     ` Jeremy Fitzhardinge
2007-02-14  2:34       ` Dan Hecht
2007-02-14  8:43         ` Gerd Hoffmann
2007-02-14  8:37       ` Jan Beulich [this message]
2007-02-14  9:15         ` [Xen-devel] " Andi Kleen
     [not found] ` <20070213221829.513618819@goop.org>
2007-02-14  9:24   ` [patch 02/21] Xen-paravirt: Handle a zero-sized VT console Gerd Hoffmann
     [not found] ` <20070213221830.707197267@goop.org>
2007-02-13 23:54   ` [patch 16/21] Xen-paravirt: Add code into head.S to handle being booted by Xen Andi Kleen
2007-02-14  0:39     ` Jeremy Fitzhardinge
2007-02-14  8:56       ` [Xen-devel] " Jan Beulich
2007-02-14 18:53     ` Jeremy Fitzhardinge
2007-02-14 20:10       ` Eric W. Biederman
2007-02-14 20:41         ` Jeremy Fitzhardinge
2007-02-14 21:06           ` Eric W. Biederman
2007-02-15  0:13             ` Jeremy Fitzhardinge
2007-02-15  1:39               ` Eric W. Biederman
2007-02-15  1:52                 ` Jeremy Fitzhardinge
2007-02-15  2:18                   ` Eric W. Biederman
2007-02-15  2:23                     ` Jeremy Fitzhardinge
2007-02-15  2:41                       ` Eric W. Biederman
2007-02-14 20:33   ` Eric W. Biederman
2007-02-14 20:42     ` Jeremy Fitzhardinge
     [not found] ` <20070213221831.150207238@goop.org>
2007-02-14 20:40   ` [patch 21/21] Xen-paravirt: Add the Xen virtual network device driver Eric W. Biederman
     [not found] ` <20070213221830.619562494@goop.org>
2007-02-14 20:45   ` [patch 15/21] Xen-paravirt: Add Xen interface header files Eric W. Biederman
2007-02-15  0:10     ` Jeremy Fitzhardinge
2007-02-15 17:32       ` Christoph Hellwig

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