linux-kernel - Re: Generic page fault (Was: libsigsegv ....)

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Message-ID: <CA+55aFw+K6aev6JPTiYxWjtJS0O8+MUwC-5=O4Gb+0mCd+tOfQ@mail.gmail.com>
Date:	Sat, 28 Feb 2015 16:41:41 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>
Subject: Re: Generic page fault (Was: libsigsegv ....)

On Sat, Feb 28, 2015 at 3:02 PM, Benjamin Herrenschmidt
<benh@...nel.crashing.org> wrote:
>
> Anyway, here's the current patch:

Ok, I think I like this approach better.

Your FAULT_FLAG_EXEC handling is wrong, though. It shouldn't check
VM_WRITE, it should check VM_EXEC. A bit too much copy-paste ;)

Btw, it's quite possible that we could just do all the PF_PROT
handling at the x86 level, before even calling the generic fault
handler. It's not like we even need the vma or the mm semaphore: if
it's a non-write protection fault, we always SIGSEGV. So why even
bother getting the locks and looking up the page tables etc?

Now, that PF_PROT handling isn't exactly performance-critical, but it
might help to remove the odd x86 special case from the generic code.

                      Linus
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