Re: [crash] Re: Latest brk patchset

[Yinghai Lu]

Jeremy Fitzhardinge wrote:
> H. Peter Anvin wrote:
>> Jeremy Fitzhardinge wrote:
>>> Yinghai Lu wrote:
>>>> could be max_pfn_mapped change in head_32.S that reduce mapping
>>>> range to _end only.
>>>>   
>>>
>>> Yes, I would say you're right.  Trimming the mapping to _end only
>>> leaves the space under the kernel avaliable for allocating pagetable
>>> from e820 space.  In this case we've got DEBUG_PAGEALLOC enabled,
>>> which inhibits the use of PSE, and BIOS corruption checking on, which
>>> eats a chunk of low memory.  In combination, there's only 0x8f000
>>> bytes free below the kernel, and it needs 0xe1000 to allocate for
>>> pagetables.
>>>
>>> Reverting 2bd2753ff46346543ab92e80df9d96366e21baa5 fixes the problem
>>> for me, though it does result in a kernel with a 73MB BSS...
>>>
>>
>> Waitaminute... there is no way we could end up with 73 MB page tables
>> unless something is seriously screwy.  Even with PAE and !PSE, we only
>> get 2 MB worth of page tables for each 1 GB mapped -- even with a 4:4
>> scheme this is only 8 MB.
> 
> Yes, something odd happened there.
> 
> Anyway, this patch fixes it.  I also removed ALLOCATOR_SLOP, because it
> is left over from when we used the bootmem allocator for the linear
> mapping pagetable, before using e820 allocation.
> 
> Did you also want to pull the changes to put the brk in .brk and rename
> the reservation symbols?
> 
>    J
> 
> The following changes since commit
> 2bd2753ff46346543ab92e80df9d96366e21baa5:
>  Yinghai Lu (1):
>        x86: put initial_pg_tables into .bss
> 
> are available in the git repository at:
> 
>  ssh://master.kernel.org/~jeremy/git/xen.git tip/x86/setup-memory
> 
> Jeremy Fitzhardinge (2):
>      x86-32: make sure we map enough to fit linear map pagetables
>      x86-32: remove ALLOCATOR_SLOP from head_32.S
> 
> arch/x86/kernel/head_32.S |   32 ++++++++++++++++++++------------
> 1 files changed, 20 insertions(+), 12 deletions(-)
> 
>> From 378c46828de3f34d94d83f08b2d6d81a0fc8f108 Mon Sep 17 00:00:00 2001
> From: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
> Date: Mon, 16 Mar 2009 12:07:54 -0700
> Subject: [PATCH] x86-32: make sure we map enough to fit linear map
> pagetables
> 
> head_32.S needs to map the kernel itself, and enough space so
> that mm/init.c can allocate space from the e820 allocator
> for the linear map of low memory.
> 
> Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
> 
> diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
> index c79741c..e929619 100644
> --- a/arch/x86/kernel/head_32.S
> +++ b/arch/x86/kernel/head_32.S
> @@ -38,8 +38,8 @@
> #define X86_VENDOR_ID    new_cpu_data+CPUINFO_x86_vendor_id
> 
> /*
> - * This is how much memory *in addition to the memory covered up to
> - * and including _end* we need mapped initially.
> + * This is how much memory in addition to the memory covered up to
> + * and including _end we need mapped initially.
>  * We need:
>  *     (KERNEL_IMAGE_SIZE/4096) / 1024 pages (worst case, non PAE)
>  *     (KERNEL_IMAGE_SIZE/4096) / 512 + 4 pages (worst case for PAE)
> @@ -52,19 +52,28 @@
>  * KERNEL_IMAGE_SIZE should be greater than pa(_end)
>  * and small than max_low_pfn, otherwise will waste some page table entries
>  */
> -LOW_PAGES = (KERNEL_IMAGE_SIZE + PAGE_SIZE_asm - 1)>>PAGE_SHIFT
> 
> #if PTRS_PER_PMD > 1
> -PAGE_TABLE_SIZE = (LOW_PAGES / PTRS_PER_PMD) + PTRS_PER_PGD
> +#define PAGE_TABLE_SIZE(pages) (((pages) / PTRS_PER_PMD) + PTRS_PER_PGD)
> #else
> -PAGE_TABLE_SIZE = (LOW_PAGES / PTRS_PER_PGD)
> +#define PAGE_TABLE_SIZE(pages) ((pages) / PTRS_PER_PGD)
> #endif
> ALLOCATOR_SLOP = 4
> 
> -INIT_MAP_SIZE = (PAGE_TABLE_SIZE + ALLOCATOR_SLOP) * PAGE_SIZE_asm
> -RESERVE_BRK(pagetables, INIT_MAP_SIZE)
> +/* Enough space to fit pagetables for the low memory linear map */
> +MAPPING_BEYOND_END = (PAGE_TABLE_SIZE(1 << (32 - PAGE_SHIFT)) * PAGE_SIZE)

that is for 4g?

YH

> 
> /*
> + * Worst-case size of the kernel mapping we need to make:
> + * the worst-case size of the kernel itself, plus the extra we need
> + * to map for the linear map.
> + */
> +KERNEL_PAGES = (KERNEL_IMAGE_SIZE + MAPPING_BEYOND_END)>>PAGE_SHIFT
> +
> +INIT_MAP_SIZE = (PAGE_TABLE_SIZE(KERNEL_PAGES) + ALLOCATOR_SLOP) *
> PAGE_SIZE_asm
> +RESERVE_BRK(pagetables, INIT_MAP_SIZE)
> +   
> +/*
>  * 32-bit kernel entrypoint; only used by the boot CPU.  On entry,
>  * %esi points to the real-mode code as a 32-bit pointer.
>  * CS and DS must be 4 GB flat segments, but we don't depend on
> @@ -197,9 +206,9 @@ default_entry:
>     loop 11b
> 
>     /*
> -     * End condition: we must map up to the end.
> +     * End condition: we must map up to the end + MAPPING_BEYOND_END.
>      */
> -    movl $pa(_end) + PTE_IDENT_ATTR, %ebp
> +    movl $pa(_end) + MAPPING_BEYOND_END + PTE_IDENT_ATTR, %ebp
>     cmpl %ebp,%eax
>     jb 10b
> 1:
> @@ -229,9 +238,9 @@ page_pde_offset = (__PAGE_OFFSET >> 20);
>     addl $0x1000,%eax
>     loop 11b
>     /*
> -     * End condition: we must map up to end
> +     * End condition: we must map up to the end + MAPPING_BEYOND_END.
>      */
> -    movl $pa(_end) + PTE_IDENT_ATTR, %ebp
> +    movl $pa(_end) + MAPPING_BEYOND_END + PTE_IDENT_ATTR, %ebp
>     cmpl %ebp,%eax
>     jb 10b
>     addl $__PAGE_OFFSET, %edi
> 

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