On Mon, Oct 01, 2012 at 12:00:26PM +0100, Stefano Stabellini wrote:
> On Sun, 30 Sep 2012, Yinghai Lu wrote:
> > After
> >
> > | commit 8548c84da2f47e71bbbe300f55edb768492575f7
> > | Author: Takashi Iwai <ti...@suse.de>
> > | Date: Sun Oct 23 23:19:12 2011 +0200
> > |
> > | x86: Fix S4 regression
> > |
> > | Commit 4b239f458 ("x86-64, mm: Put early page table high") causes a S4
> > | regression since 2.6.39, namely the machine reboots occasionally at S4
> > | resume. It doesn't happen always, overall rate is about 1/20. But,
> > | like other bugs, once when this happens, it continues to happen.
> > |
> > | This patch fixes the problem by essentially reverting the memory
> > | assignment in the older way.
> >
> > Have some page table around 512M again, that will prevent kdump to find 512M
> > under 768M.
> >
> > We need revert that reverting, so we could put page table high again for
> > 64bit.
> >
> > Takashi agreed that S4 regression could be something else.
> >
> > https://lkml.org/lkml/2012/6/15/182
> >
> > Signed-off-by: Yinghai Lu <ying...@kernel.org>
> > ---
> > arch/x86/mm/init.c | 2 +-
> > 1 files changed, 1 insertions(+), 1 deletions(-)
> >
> > diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
> > index 9f69180..aadb154 100644
> > --- a/arch/x86/mm/init.c
> > +++ b/arch/x86/mm/init.c
> > @@ -76,8 +76,8 @@ static void __init find_early_table_space(struct
> > map_range *mr,
> > #ifdef CONFIG_X86_32
> > /* for fixmap */
> > tables += roundup(__end_of_fixed_addresses * sizeof(pte_t), PAGE_SIZE);
> > -#endif
> > good_end = max_pfn_mapped << PAGE_SHIFT;
> > +#endif
> >
> > base = memblock_find_in_range(start, good_end, tables, PAGE_SIZE);
> > if (!base)
>
> Isn't this going to cause init_memory_mapping to allocate pagetable
> pages from memory not yet mapped?
> Last time I spoke with HPA and Thomas about this, they seem to agree
> that it isn't a very good idea.
> Also, it is proven to cause a certain amount of headaches on Xen,
> see commit d8aa5ec3382e6a545b8f25178d1e0992d4927f19.
>
Any comments, thoughts? hpa? Yinghai?
So it seems that during init_memory_mapping Xen needs to modify page table
bits and the memory where the page tables live needs to be direct mapped at
that time.
Since we now call init_memory_mapping for every E820_RAM range sequencially,
the only way to satisfy Xen is to find_early_page_table_space (good_end needs
to be within memory already mapped at the time) for every init_memory_mapping
call.
What do you think Yinghai?
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