linux-kernel - Re: [PATCH] x86: extend e820 ealy_res support 32bit

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Date:	Sat, 24 May 2008 09:54:53 +0100
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Yinghai Lu <yhlu.kernel@...il.com>
CC:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: extend e820 ealy_res support 32bit - fix v2

Yinghai Lu wrote:
> [PATCH] x86: extend e820 ealy_res support 32bit - fix v2
>
> use find_e820_area to find addess for new RAMDISK, instead of using ram blindly
>
> also print out low ram and bootmap info
>
> v2: remove extra -1 in reaseve_early calling
>     panic if can not find space for new RAMDISK
>   

OK, I've fixed earlyprintk=xen, so I can finally get some useful 
debugging information.

With this patch it still crashes, but outputs:

(early) Reserving virtual address space above 0xf57fe000
(early) Linux version 2.6.26-rc3-sched-devel.git (jeremy@...tim.goop.org) (gcc version 4.1.2 20070925 (Red Hat 4.1.2-33)) #466 SMP PREEMPT Sat May 24 01:05:41 PDT 2008
(early) ACPI in unprivileged domain disabled
(early) BIOS-provided physical RAM map:
(early)  Xen: 0000000000000000 - 000000000009f000 (usable)
(early)  Xen: 0000000000100000 - 0000000010000000 (usable)
(early) console [xenboot0] enabled
(early) debug: ignoring loglevel setting.
(early)  limit_regions start: 0000000000000000 - 000000000009f000 (early) (usable)
(early)  limit_regions start: 0000000000100000 - 0000000010000000 (early) (usable)
(early)  limit_regions endfunc: 0000000000000000 - 000000000009f000 (early) (usable)
(early)  limit_regions endfunc: 0000000000100000 - 0000000010000000 (early) (usable)
(early) user-defined physical RAM map:
(early)  user: 0000000000000000 - 000000000009f000 (early) (usable)
(early)  user: 0000000000100000 - 0000000010000000 (early) (usable)
(early) 0MB HIGHMEM available.
(early) 256MB LOWMEM available.
(early)   low ram: 0102c000 - 10000000
(early)   bootmap 0102c000 - 0102e000
(early)   early res: 0 [0-fff] BIOS data page
(early)   early res: 1 [1000-1fff] EX TRAMPOLINE
(early)   early res: 2 [6000-6fff] TRAMPOLINE
(early)   early res: 3 [102c000-102dfff] BOOTMAP
(early) Scan SMP from c0000000 for 1024 bytes.
(early) Scan SMP from c009fc00 for 1024 bytes.
(early) Scan SMP from c00f0000 for 65536 bytes.
(early) Scan SMP from c00c2c20 for 1024 bytes.
(early) NX (Execute Disable) protection: active
[crash]

Hm, I think this is the problem:

		/*
		 * don't need to reserve again, already reserved early
		 * in i386_start_kernel
		 */

A Xen pv boot doesn't presently go via i386_start_kernel; it goes 
directly from xen_start_kernel to start_kernel (you can see that the 
"early res" lines are missing important things like the kernel code and 
pagetables).

I tried making xen_start_kernel directly call i386_start_kernel, and it 
nearly works.  The problem is that the initial address space layout for 
a Xen domain is:

    kernel
    ramdisk
    init pagetable

which means that in

	reserve_early(__pa_symbol(&_text), __pa_symbol(&_end), "TEXT DATA BSS");

#ifdef CONFIG_BLK_DEV_INITRD
	/* Reserve INITRD */
	if (boot_params.hdr.type_of_loader && boot_params.hdr.ramdisk_image) {
		u64 ramdisk_image = boot_params.hdr.ramdisk_image;
		u64 ramdisk_size  = boot_params.hdr.ramdisk_size;
		u64 ramdisk_end   = ramdisk_image + ramdisk_size;
		reserve_early(ramdisk_image, ramdisk_end, "RAMDISK");
	}
#endif
	reserve_early(__pa_symbol(&_end), init_pg_tables_end, "INIT_PG_TABLE");

the INIT_PG_TABLE reserve_early() will panic because it partially 
overlaps with the RAMDISK reservation.

    J
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