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

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Date:	Sat, 24 May 2008 12:57:11 -0700
From:	"Yinghai Lu" <yhlu.kernel@...il.com>
To:	"Jeremy Fitzhardinge" <jeremy@...p.org>
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

On Sat, May 24, 2008 at 1:54 AM, Jeremy Fitzhardinge <jeremy@...p.org> wrote:
> 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.

great. i guess 64bit XEN pv will call x86_64_start_kernel.

INIT_PG_TABLE is right after "TEXT DATA BSS".

So you bootloader will don't leave space between kernel and ramdisk?

or need to put INIT_PG_TABLE before end of BSS like 64bit did....

YH
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