Avi wrote: >The fact that the check is only done on i386 and not on x86_64 > may come from one of > > - an oversight > - by the time x86_64 processors came along, the problem with > conflicting sizes was resolved > - the whole thing is bogus > > Copying hpa who may be in a position to find out which.
Talking to hpa it is more of the last. For more than just this reason. Since the whole area of initial page tables seems to be rather sensitive and easy to break there have been discussions and plans to come up with a rewrite to improve on all those shortcomings. The detail I am not agreeing with hpa is the fixup for the immediate breakage at head. IMO right now the code just has regressed and that should be fixed as soon as possible. Plus doing a specific and small fix allows that to be applicable to stable (which again still depends on things being upstream). Hence the re-send in the hope that on the larger scale the may be agreement on the immediate fix. I am not doubting the usefulness or need of a better solution, but I think that having a remedy of the current situation just until then has enough benefit to be considered. -Stefan >From 1d5cc3971716a039c91abc18cb6f9bcbe5dde490 Mon Sep 17 00:00:00 2001 From: Stefan Bader <stefan.ba...@canonical.com> Date: Fri, 13 Jul 2012 15:16:33 +0200 Subject: [PATCH] x86/mm: Limit 2/4M size calculation to x86_32 commit 722bc6b (x86/mm: Fix the size calculation of mapping tables) did modify the extra space calculation for mapping tables in order to make up for the first 2/4M memory range using 4K pages. However this setup is only used when compiling for 32bit. On 64bit there is only the trailing area of 4K pages (which is already added). The code was already adapted once for things went wrong on a 8TB machine (bd2753b x86/mm: Only add extra pages count for the first memory range during pre-allocation early page table space), but it looks a bit like it currently would overdo things for 64bit. I only noticed while bisecting for the reason I could not make a crash kernel boot (which ended up on this patch). Signed-off-by: Stefan Bader <stefan.ba...@canonical.com> Cc: sta...@vger.kernel.org # v3.5 Cc: WANG Cong <xiyou.wangc...@gmail.com> Cc: Yinghai Lu <ying...@kernel.org> Cc: Tejun Heo <t...@kernel.org> --- arch/x86/mm/init.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c index e0e6990..28a1c99 100644 --- a/arch/x86/mm/init.c +++ b/arch/x86/mm/init.c @@ -60,10 +60,11 @@ static void __init find_early_table_space(struct map_range *mr, unsigned long en extra = end - ((end>>PMD_SHIFT) << PMD_SHIFT); #ifdef CONFIG_X86_32 extra += PMD_SIZE; -#endif + /* The first 2/4M doesn't use large pages. */ if (mr->start < PMD_SIZE) extra += mr->end - mr->start; +#endif ptes = (extra + PAGE_SIZE - 1) >> PAGE_SHIFT; } else -- 1.7.10.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/