On Fri, 5 Oct 2012, Yinghai Lu wrote:
> On Thu, Oct 4, 2012 at 2:54 PM, H. Peter Anvin <h...@zytor.com> wrote:
> >
> > See my other post. This is bringing up the Kernel Summit algorithm again.
> >
>
> sure. please check if you are ok with attached one on top of x86/mm2
>
> Subject: [PATCH] x86: get early page table from BRK
>
> set pgt_buf early from BRK, and use it to map page table at first.
>
> also use the left at first, then use new extend one.
>
> Signed-off-by: Yinghai Lu <ying...@kernel.org>
If I read the patch correctly, it wouldn't actually change the pagetable
allocation flow or implement Peter's suggestion.
However it would pre-map (pgt_buf_start-pgt_buf_top) using brk memory.
So, if that's correct, we could remove the early_memremap call from
alloc_low_page and map_low_page, right?
Also the patch introduces an additional range of pagetable pages
(early_pgt_buf_start-early_pgt_buf_top) and that would need to be
communicated somehow to Xen (that at the moment assumes that the range
is pgt_buf_start-pgt_buf_top. Pretty bad).
Overall I still prefer Peter's suggestion :)
> ---
> arch/x86/include/asm/init.h | 4 ++++
> arch/x86/include/asm/pgtable.h | 1 +
> arch/x86/kernel/setup.c | 2 ++
> arch/x86/mm/init.c | 23 +++++++++++++++++++++++
> arch/x86/mm/init_32.c | 8 ++++++--
> arch/x86/mm/init_64.c | 8 ++++++--
> 6 files changed, 42 insertions(+), 4 deletions(-)
>
> Index: linux-2.6/arch/x86/include/asm/pgtable.h
> ===================================================================
> --- linux-2.6.orig/arch/x86/include/asm/pgtable.h
> +++ linux-2.6/arch/x86/include/asm/pgtable.h
> @@ -599,6 +599,7 @@ static inline int pgd_none(pgd_t pgd)
>
> extern int direct_gbpages;
> void init_mem_mapping(void);
> +void early_alloc_pgt_buf(void);
>
> /* local pte updates need not use xchg for locking */
> static inline pte_t native_local_ptep_get_and_clear(pte_t *ptep)
> Index: linux-2.6/arch/x86/kernel/setup.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/kernel/setup.c
> +++ linux-2.6/arch/x86/kernel/setup.c
> @@ -950,6 +950,8 @@ void __init setup_arch(char **cmdline_p)
>
> reserve_ibft_region();
>
> + early_alloc_pgt_buf();
> +
> /*
> * Need to conclude brk, before memblock_x86_fill()
> * it could use memblock_find_in_range, could overlap with
> Index: linux-2.6/arch/x86/mm/init.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/mm/init.c
> +++ linux-2.6/arch/x86/mm/init.c
> @@ -21,6 +21,10 @@ unsigned long __initdata pgt_buf_start;
> unsigned long __meminitdata pgt_buf_end;
> unsigned long __meminitdata pgt_buf_top;
>
> +unsigned long __initdata early_pgt_buf_start;
> +unsigned long __meminitdata early_pgt_buf_end;
> +unsigned long __meminitdata early_pgt_buf_top;
> +
> int after_bootmem;
>
> int direct_gbpages
> @@ -291,6 +295,11 @@ static void __init find_early_table_spac
> if (!base)
> panic("Cannot find space for the kernel page tables");
>
> + init_memory_mapping(base, base + tables);
> + printk(KERN_DEBUG "kernel direct mapping tables from %#llx to %#llx @
> [mem %#010lx-%#010lx]\n",
> + base, base + tables - 1, early_pgt_buf_start << PAGE_SHIFT,
> + (early_pgt_buf_end << PAGE_SHIFT) - 1);
> +
> pgt_buf_start = base >> PAGE_SHIFT;
> pgt_buf_end = pgt_buf_start;
> pgt_buf_top = pgt_buf_start + (tables >> PAGE_SHIFT);
> @@ -437,6 +446,20 @@ void __init init_mem_mapping(void)
> early_memtest(0, max_pfn_mapped << PAGE_SHIFT);
> }
>
> +RESERVE_BRK(early_pgt_alloc, 16384);
> +
> +void __init early_alloc_pgt_buf(void)
> +{
> + unsigned long tables = 13864;
> + phys_addr_t base;
> +
> + base = __pa(extend_brk(tables, PAGE_SIZE));
> +
> + early_pgt_buf_start = base >> PAGE_SHIFT;
> + early_pgt_buf_end = early_pgt_buf_start;
> + early_pgt_buf_top = early_pgt_buf_start + (tables >> PAGE_SHIFT);
> +}
> +
> /*
> * devmem_is_allowed() checks to see if /dev/mem access to a certain address
> * is valid. The argument is a physical page number.
> Index: linux-2.6/arch/x86/mm/init_32.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/mm/init_32.c
> +++ linux-2.6/arch/x86/mm/init_32.c
> @@ -61,10 +61,14 @@ bool __read_mostly __vmalloc_start_set =
>
> static __init void *alloc_low_page(void)
> {
> - unsigned long pfn = pgt_buf_end++;
> + unsigned long pfn;
> void *adr;
>
> - if (pfn >= pgt_buf_top)
> + if (early_pgt_buf_end < early_pgt_buf_top)
> + pfn = early_pgt_buf_end++;
> + else if (pgt_buf_end < pgt_buf_top)
> + pfn = pgt_buf_end++;
> + else
> panic("alloc_low_page: ran out of memory");
>
> adr = __va(pfn * PAGE_SIZE);
> Index: linux-2.6/arch/x86/mm/init_64.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/mm/init_64.c
> +++ linux-2.6/arch/x86/mm/init_64.c
> @@ -318,7 +318,7 @@ void __init cleanup_highmap(void)
>
> static __ref void *alloc_low_page(unsigned long *phys)
> {
> - unsigned long pfn = pgt_buf_end++;
> + unsigned long pfn;
> void *adr;
>
> if (after_bootmem) {
> @@ -328,7 +328,11 @@ static __ref void *alloc_low_page(unsign
> return adr;
> }
>
> - if (pfn >= pgt_buf_top)
> + if (early_pgt_buf_end < early_pgt_buf_top)
> + pfn = early_pgt_buf_end++;
> + else if (pgt_buf_end < pgt_buf_top)
> + pfn = pgt_buf_end++;
> + else
> panic("alloc_low_page: ran out of memory");
>
> adr = early_memremap(pfn * PAGE_SIZE, PAGE_SIZE);
--
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