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From: Eduardo Habkost <ehabkost@redhat.com>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ian Campbell <ijc@hellion.org.uk>,
	Alexander van Heukelum <heukelum@mailshack.com>,
	Ingo Molnar <mingo@elte.hu>,
	Alexander van Heukelum <heukelum@fastmail.fm>,
	Andi Kleen <ak@suse.de>, Thomas Gleixner <tglx@linutronix.de>,
	Jeremy Fitzhardinge <jeremy@goop.org>,
	Mark McLoughlin <markmc@redhat.com>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC] use realmode code to reserve end-of-conventional-memory to 1MB
Date: Wed, 5 Mar 2008 13:53:20 -0300	[thread overview]
Message-ID: <20080305165320.GJ20230@blackpad> (raw)
In-Reply-To: <47CEC561.6050008@zytor.com>

On Wed, Mar 05, 2008 at 08:08:01AM -0800, H. Peter Anvin wrote:
> Eduardo Habkost wrote:
> >>
> >>diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
> >>index 3bad477..2341492 100644
> >>--- a/arch/x86/xen/setup.c
> >>+++ b/arch/x86/xen/setup.c
> >>@@ -38,7 +38,8 @@ char * __init xen_memory_setup(void)
> >> 	unsigned long max_pfn = xen_start_info->nr_pages;
> >> 
> >> 	e820.nr_map = 0;
> >>-	add_memory_region(0, PFN_PHYS(max_pfn), E820_RAM);
> >>+	add_memory_region(0, LOWMEMSIZE(), E820_RAM);
> >>+	add_memory_region(HIGH_MEMORY, PFN_PHYS(max_pfn)-HIGH_MEMORY, 
> >>E820_RAM);
> >
> >Won't this waste 300+ KB of Perfectly Good RAM? Or I understood it
> >incorrectly?
> >
> >I am aware that it would take more work to tell all kernel code that it
> >shouldn't look for BIOS data on this region when running as a domU guest,
> >but it seems that it would be a better solution.
> >
> 
> No, the right thing is for Xen to not try to map RAM in this area.

Why? If the Xen host is telling us there is valid RAM in this area,
why can't we use it?

Existing Xen hosts use those physical address ranges for RAM. We can't
fix this on the e820 map on the guest side without making otherwise-valid
RAM unused.

-- 
Eduardo

  reply	other threads:[~2008-03-05 16:56 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 [this message]
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
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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