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Date: Fri, 13 Mar 2009 13:27:28 -0700
From: Jeremy Fitzhardinge <jeremy@...p.org>
To: Yinghai Lu <yinghai@...nel.org>
CC: "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
the arch/x86 maintainers <x86@...nel.org>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL] x86: add brk allocator for very early allocations
Yinghai Lu wrote:
> Jeremy Fitzhardinge wrote:
>
>> Yinghai Lu wrote:
>>
>>> could have more explanation about the 1M size.
>>> because initial_pg_tables will sit in it. please consider to add
>>> something like
>>>
>>> in head_32.S
>>>
>>> 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
>>> #else
>>> PAGE_TABLE_SIZE = (LOW_PAGES / PTRS_PER_PGD)
>>> #endif
>>> ALLOCATOR_SLOP = 4
>>>
>>>
>> OK, how does this look:
>>
>> The following changes since commit
>> 21e8ba72daf5d7f0af33968f873499c85f96ccef:
>> Jeremy Fitzhardinge (1):
>> x86: use brk allocation for DMI
>>
>> are available in the git repository at:
>>
>> git://git.kernel.org/pub/scm/linux/kernel/git/jeremy/xen.git push/x86/brk
>>
>> Jeremy Fitzhardinge (1):
>> x86: allow extend_brk users to reserve brk space
>>
>> Yinghai Lu (1):
>> x86-32: compute initial mapping size more accurately
>>
>> arch/x86/include/asm/page_32_types.h | 5 +++++
>> arch/x86/include/asm/setup.h | 30 ++++++++++++++++++++++++++++++
>> arch/x86/kernel/head_32.S | 4 +++-
>> arch/x86/kernel/setup.c | 2 ++
>> arch/x86/kernel/vmlinux_32.lds.S | 4 +++-
>> arch/x86/kernel/vmlinux_64.lds.S | 4 +++-
>> 6 files changed, 46 insertions(+), 3 deletions(-)
>>
>> git diff 21e8ba72daf5d7f0af33968f873499c85f96ccef..push/x86/brk
>> diff --git a/arch/x86/include/asm/page_32_types.h
>> b/arch/x86/include/asm/page_32_types.h
>> index f1e4a79..0f915ae 100644
>> --- a/arch/x86/include/asm/page_32_types.h
>> +++ b/arch/x86/include/asm/page_32_types.h
>> @@ -39,6 +39,11 @@
>> #define __VIRTUAL_MASK_SHIFT 32
>> #endif /* CONFIG_X86_PAE */
>>
>> +/*
>> + * Kernel image size is limited to 512 MB (see in
>> arch/x86/kernel/head_32.S)
>> + */
>> +#define KERNEL_IMAGE_SIZE (512 * 1024 * 1024)
>> +
>> #ifndef __ASSEMBLY__
>>
>> /*
>> diff --git a/arch/x86/include/asm/setup.h b/arch/x86/include/asm/setup.h
>> index 366d366..61b126b 100644
>> --- a/arch/x86/include/asm/setup.h
>> +++ b/arch/x86/include/asm/setup.h
>> @@ -104,6 +104,29 @@ extern struct boot_params boot_params;
>> extern unsigned long _brk_end;
>> void *extend_brk(size_t size, size_t align);
>>
>> +/*
>> + * Reserve space in the brk section. The name must be unique within
>> + * the file, and somewhat descriptive. The size is in bytes. Must be
>> + * used at file scope.
>> + *
>> + * (This uses a temp function to wrap the asm so we can pass it the
>> + * size parameter; otherwise we wouldn't be able to. We can't use a
>> + * "section" attribute on a normal variable because it always ends up
>> + * being @progbits, which ends up allocating space in the vmlinux
>> + * executable.)
>> + */
>> +#define RESERVE_BRK(name,sz) \
>> + static void __section(.discard) __used \
>> + __brk_reservation_fn_##name##__(void) { \
>> + asm volatile ( \
>> + ".pushsection .brk_reservation,\"aw\",@nobits;" \
>> + "__brk_reservation_" #name "__:" \
>> + " 1:.skip %c0;" \
>> + " .size __brk_reservation_" #name "__, . - 1b;" \
>> + " .popsection" \
>> + : : "i" (sz)); \
>> + }
>> +
>> #ifdef __i386__
>>
>> void __init i386_start_kernel(void);
>> @@ -115,6 +138,13 @@ void __init x86_64_start_reservations(char
>> *real_mode_data);
>>
>> #endif /* __i386__ */
>> #endif /* _SETUP */
>> +#else
>> +#define RESERVE_BRK(name,sz) \
>> + .pushsection .brk_reservation,"aw",@nobits; \
>> +__brk_reservation_##name##__: \
>> +1: .skip sz; \
>> + .size __brk_reservation_##name##__,.-1b; \
>> + .popsection
>> #endif /* __ASSEMBLY__ */
>> #endif /* __KERNEL__ */
>>
>> diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
>> index d243437..80dc05e 100644
>> --- a/arch/x86/kernel/head_32.S
>> +++ b/arch/x86/kernel/head_32.S
>> @@ -54,7 +54,7 @@
>> *
>> * This should be a multiple of a page.
>> */
>> -LOW_PAGES = 1<<(32-PAGE_SHIFT_asm)
>> +LOW_PAGES = (KERNEL_IMAGE_SIZE + PAGE_SIZE_asm - 1)>>PAGE_SHIFT
>>
>> /*
>> * To preserve the DMA pool in PAGEALLOC kernels, we'll allocate
>> @@ -75,6 +75,8 @@ ALLOCATOR_SLOP = 4
>>
>> INIT_MAP_BEYOND_END = BOOTBITMAP_SIZE + (PAGE_TABLE_SIZE +
>> ALLOCATOR_SLOP)*PAGE_SIZE_asm
>>
>
> no user for INIT_MAP_BEYOND_END any more.
>
There are several remaining references:
: abulafia:pts/0; grep INIT_MAP_BEYOND_END arch/x86/kernel/head_32.S
INIT_MAP_BEYOND_END = BOOTBITMAP_SIZE + (PAGE_TABLE_SIZE + ALLOCATOR_SLOP)*PAGE_SIZE_asm
* and PAGE_OFFSET for up to _end+sizeof(page tables)+INIT_MAP_BEYOND_END.
* End condition: we must map up to and including INIT_MAP_BEYOND_END
leal (INIT_MAP_BEYOND_END+PTE_IDENT_ATTR)(%edi),%ebp
* End condition: we must map up to and including INIT_MAP_BEYOND_END
leal (INIT_MAP_BEYOND_END+PTE_IDENT_ATTR)(%edi),%ebp
Are you saying they're redundant and should be removed?
> could add
> /*
> * Build-time check on the image size:
> */
> ASSERT((_end - LOAD_OFFSET <= KERNEL_IMAGE_SIZE),
> "kernel image bigger than KERNEL_IMAGE_SIZE")
>
>
> for 32bit
>
I guess we could, but it doesn't seem very urgent.
J
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