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Date: Tue, 20 Jan 2009 13:07:09 +0100 From: Nick Piggin <npiggin@...e.de> To: Ingo Molnar <mingo@...e.hu> Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Linus Torvalds <torvalds@...ux-foundation.org> Subject: Re: [patch] x86: optimise page fault entry On Tue, Jan 20, 2009 at 11:09:46AM +0100, Ingo Molnar wrote: > > * Nick Piggin <npiggin@...e.de> wrote: > > > Hi, > > > > Sorry for the delay with this. The kernel ended up unbootable for me > > when I last dusted off the patch, so I couldn't test it and then > > promptly got sidetracked with other things. > > > > Anyway, this one is tested with a boot, some basic segfault sigbus etc > > tests, and passes various of the mmap and mprotect etc. ltp tests. > > > > Ingo, would you merge this into the x86 tree, please? (unless Linus has > > any objections to this version) > > -tip testing found a 32-bit boot regression, caused by this patch. The > bootup hangs early, during the WP write-test check: > > [ 0.004000] .data : 0xc0691f05 - 0xc09c746c (3285 kB) > [ 0.004000] .text : 0xc0100000 - 0xc0691f05 (5703 kB) > [ 0.004000] Checking if this processor honours the WP bit even in supervisor mode... > > i've excluded x86/mm from tip/master for now, you can find the broken tree > in the tip/tip.x86.mm.broken [v2.6.29-rc2-1069-g583f1b9] branch that i > just pushed out: > > git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git tip.x86.mm.broken Gah, I knew I should have tested with 32-bit. Sorry, I had actually tested it at some point, so I must have dropped this hunk along the way :( > Also, a patch structure sidenote, the diffstat is rather large: > > arch/x86/mm/fault.c | 436 ++++++++++++++++++++++++++++++--------------------- > 1 files changed, 255 insertions(+), 181 deletions(-) > > this shuffles 300 lines of highly critical x86 code around - which makes > me nervous. A finegrained, bisectable series would be far more debuggable. > Had we such a lineup i could have auto-bisected it for you already - while > now you have to see which bit of the ~500 lines of code flux broke the > 32-bit WP test. > > This hang might be easy to find and fix (the WP detect logic is simple), > but other failure modes might be less debuggable and this codepath deals > with a lot of obscure details like CPU errata. So it would be really nice > to have a finegrained splitup of this patch. I guess breaking out the shuffling of parameters (where this bug lies), breaking out functions from do_page_fault, and added branch annotations could be done.... that would still leave a fair hunk in the breakout patch, which I didn't see a really pleasing way to split out. > Three separate testsystems triggered this hang so it should be readily > reproducible. Yes, thanks, Nick --- arch/x86/mm/fault.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) Index: linux-2.6/arch/x86/mm/fault.c =================================================================== --- linux-2.6.orig/arch/x86/mm/fault.c +++ linux-2.6/arch/x86/mm/fault.c @@ -828,7 +828,7 @@ void __kprobes do_page_fault(struct pt_r return; /* Can handle a stale RO->RW TLB */ - if (spurious_fault(address, error_code)) + if (spurious_fault(error_code, address)) return; /* -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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