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From: "Alexander van Heukelum" <heukelum@fastmail.fm>
To: "Mark McLoughlin" <markmc@redhat.com>,
	"Alexander van Heukelum" <heukelum@mailshack.com>
Cc: "Ingo Molnar" <mingo@elte.hu>,
	"Ian Campbell" <ijc@hellion.org.uk>,
	"H. Peter Anvin" <hpa@zytor.com>, "Andi Kleen" <ak@suse.de>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Jeremy Fitzhardinge" <jeremy@goop.org>,
	"LKML" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] reserve end-of-conventional-memory to 1MB on 32-bit
Date: Fri, 29 Feb 2008 19:38:43 +0100	[thread overview]
Message-ID: <1204310323.24514.1239870063@webmail.messagingengine.com> (raw)
In-Reply-To: <1204305247.2037.2.camel@muff>

On Fri, 29 Feb 2008 17:14:07 +0000, "Mark McLoughlin"
<markmc@redhat.com> said:
> On Fri, 2008-02-29 at 12:49 +0100, Alexander van Heukelum wrote:
> > This patch adds explicit detection of the EBDA and reservation
> > of the rom and adapter address space 0xa0000-0x100000 to the
> > i386 kernels. It uses reserve_bootmem instead of reserve_early,
> > because reserve_early is not yet available on i386.
> > 
> > Before this patch, the EBDA size was hardcoded as 4Kb. Also, the 
> > reservation of the adapter range was done by modifying the e820
> > map which is now not necessary any longer, and the code is removed
> > from copy_e820_map.
> > 
> > The changes in e820_64.c are only a change in the comment above
> > copy_e820_map, and some changes of the types of local variables
> > in that function such that the 32 and 64 bit versions become equal.
> > 
> > Signed-off-by: Alexander van Heukelum <heukelum@fastmail.fm>
> > 
> > ---
> > 
> > On Thu, Feb 28, 2008 at 09:09:56PM +0000, Ian Campbell wrote:
> > > On Thu, 2008-02-28 at 14:13 +0100, Alexander van Heukelum wrote:
> > > > The 32-bit code still uses reserve_bootmem, so this is not really
> > > > a unification with the 64-bit version of the ebda reservation code,
> > > > but at least it provides the same detection logic and reserves the
> > > > same areas.
> > > > 
> > > > This does not crash immediately on qemu. No further testing was
> > > > done! Otherwise:
> > > 
> > > I haven't tested extensively either but it does seem to solve the
> > > problem for Xen.
> > > 
> > > Thanks!
> > > Ian
> > 
> > Thank you!
> > 
> > Ingo,
> > 
> > I think this is ready for -x86#testing.
> > It boots to a small userspace in qemu (i386).
> > If I should separate the cleanups, let me know.
> 
> 	I haven't investigated in any detail, but with 2.6.25-rc3 and your
> patch I'm seeing a Xen guest hit this BUG:
> 
> void __init smp_alloc_memory(void)
> {
>         trampoline_base = alloc_bootmem_low_pages(PAGE_SIZE);
>         /*                                                                
>          * Has to be in very low memory so we can execute                 
>          * real-mode AP code.                                             
>          */
>         if (__pa(trampoline_base) >= 0x9F000)
>                 BUG();
> }
> 
> 	Stack looks like:
> 
>   [<c137ef97>] smp_alloc_memory+0x25  <--
>   [<c137ef97>] smp_alloc_memory+0x25 
>   [<c137a500>] setup_arch+0x28e 
>   [<c13735f7>] start_kernel+0x7a 
>   [<c1379240>] xen_start_kernel+0x300 

Ouch.

My first guess is that the BIOS data area is completely non-existent for
Xen.
Is it guaranteed that the memory is zeroed out on boot? In that case we
can
special-case it easily:

change:
        /* Paranoia: should never happen, but... */
        if (lowmem >= 0x100000)
                lowmem = 0xa0000;

into:
        /* Strange case, like Xen ;) */
        if (lowmem == 0 || lowmem >= 0x100000)
                lowmem = 0x9f000;

Can you test that?

Greetings,
    Alexander
-- 
  Alexander van Heukelum
  heukelum@fastmail.fm

-- 
http://www.fastmail.fm - Send your email first class


  reply	other threads:[~2008-02-29 18:38 UTC|newest]

Thread overview: 62+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-02-24 17:46 [PATCH] Fix alignment of early reservation for EBDA Alexander van Heukelum
2008-02-24 19:27 ` Andi Kleen
2008-02-24 19:41 ` Ingo Molnar
2008-02-24 20:53   ` Alexander van Heukelum
2008-02-25  2:18 ` H. Peter Anvin
2008-02-25 16:54   ` Alexander van Heukelum
2008-02-25 17:01     ` Ingo Molnar
2008-02-25 18:07       ` [PATCH] reserve_early end-of-conventional-memory to 1MB Alexander van Heukelum
2008-02-25 18:13         ` H. Peter Anvin
2008-02-25 19:46           ` Alexander van Heukelum
2008-02-25 21:17             ` H. Peter Anvin
2008-02-26  9:30             ` Ingo Molnar
2008-02-27 14:26               ` Andi Kleen
2008-02-27 14:38               ` [PATCH] reserve_early end-of-conventional-memory to 1MB II - some numbers to put it into perspective Andi Kleen
2008-02-27 16:44                 ` H. Peter Anvin
2008-02-27 20:01                 ` Alexander van Heukelum
2008-02-28 13:13         ` [PATCH] reserve end-of-conventional-memory to 1MB on 32-bit Alexander van Heukelum
2008-02-28 13:28           ` [RFC] use realmode code to reserve end-of-conventional-memory to 1MB Alexander van Heukelum
2008-02-28 21:12             ` Ian Campbell
2008-02-28 21:14               ` H. Peter Anvin
2008-02-28 23:16                 ` Ian Campbell
2008-02-29 20:00                   ` Ingo Molnar
2008-03-04 11:41                   ` Mark McLoughlin
2008-03-04 14:33                     ` Ingo Molnar
2008-03-04 15:12                       ` Ian Campbell
2008-03-04 15:13                       ` Jeremy Fitzhardinge
2008-03-04 15:25                         ` Ingo Molnar
2008-03-04 16:02                           ` Jeremy Fitzhardinge
2008-03-04 16:15                             ` Ingo Molnar
2008-03-04 16:15                       ` Mark McLoughlin
2008-03-04 16:23                         ` Ingo Molnar
2008-03-04 17:44                   ` Jeremy Fitzhardinge
2008-03-05 15:59                   ` Eduardo Habkost
2008-03-05 16:08                     ` H. Peter Anvin
2008-03-05 16:53                       ` Eduardo Habkost
2008-03-05 17:28                         ` H. Peter Anvin
2008-03-05 17:28                           ` Jeremy Fitzhardinge
2008-03-05 17:38                             ` H. Peter Anvin
2008-03-05 16:38                     ` Jeremy Fitzhardinge
2008-03-05 17:27                       ` H. Peter Anvin
2008-02-28 21:09           ` [PATCH] reserve end-of-conventional-memory to 1MB on 32-bit Ian Campbell
2008-02-29 11:49             ` Alexander van Heukelum
2008-02-29 17:14               ` Mark McLoughlin
2008-02-29 18:38                 ` Alexander van Heukelum [this message]
2008-02-29 18:44                   ` H. Peter Anvin
2008-02-29 18:56                     ` Alexander van Heukelum
2008-02-29 22:06                   ` Mark McLoughlin
2008-02-29 22:26                     ` Alexander van Heukelum
2008-03-01 16:09                     ` [PATCH] reserve end-of-conventional-memory to 1MB on 32-bit v2 Alexander van Heukelum
2008-03-01 16:12                       ` [PATCH] reserve end-of-conventional-memory to 1MB on 64-bit add-on Alexander van Heukelum
2008-03-04 11:44                       ` [PATCH] reserve end-of-conventional-memory to 1MB on 32-bit v2 Mark McLoughlin
2008-03-04 13:31                         ` Alexander van Heukelum
2008-03-04 14:49                         ` Ingo Molnar
2008-03-04 15:16                           ` Mark McLoughlin
2008-03-04 15:24                             ` Ingo Molnar
2008-03-04 15:18                         ` Jeremy Fitzhardinge
2008-03-04 16:51                           ` Alexander van Heukelum
2008-03-04 17:05                             ` H. Peter Anvin
2008-03-04 17:11                             ` Jeremy Fitzhardinge
2008-03-04 18:57                               ` [PATCH] reserve end-of-conventional-memory to 1MB, 32-bit, use paravirt_enabled Alexander van Heukelum
2008-03-04 19:12                                 ` [PATCH] reserve end-of-conventional-memory to 1MB, 64-bit, " Alexander van Heukelum
2008-02-27 14:25     ` [PATCH] Fix alignment of early reservation for EBDA Andi Kleen

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