From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f54.google.com (mail-pa0-f54.google.com [209.85.220.54]) by kanga.kvack.org (Postfix) with ESMTP id 1E4356B0253 for ; Fri, 25 Sep 2015 19:19:00 -0400 (EDT) Received: by pacfv12 with SMTP id fv12so120305031pac.2 for ; Fri, 25 Sep 2015 16:18:59 -0700 (PDT) Received: from blackbird.sr71.net (www.sr71.net. [198.145.64.142]) by mx.google.com with ESMTP id ey7si8654007pab.142.2015.09.25.16.18.57 for ; Fri, 25 Sep 2015 16:18:58 -0700 (PDT) Subject: Re: [PATCH 10/26] x86, pkeys: notify userspace about protection key faults References: <20150916174903.E112E464@viggo.jf.intel.com> <20150916174906.51062FBC@viggo.jf.intel.com> <20150924092320.GA26876@gmail.com> <20150924093026.GA29699@gmail.com> <560435B4.1010603@sr71.net> <20150925071119.GB15753@gmail.com> From: Dave Hansen Message-ID: <5605D660.8000009@sr71.net> Date: Fri, 25 Sep 2015 16:18:56 -0700 MIME-Version: 1.0 In-Reply-To: <20150925071119.GB15753@gmail.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Ingo Molnar Cc: x86@kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Linus Torvalds , Andrew Morton , Peter Zijlstra , Thomas Gleixner On 09/25/2015 12:11 AM, Ingo Molnar wrote: >>> > > Btw., how does pkey support interact with hugepages? >> > >> > Surprisingly little. I've made sure that everything works with huge pages and >> > that the (huge) PTEs and VMAs get set up correctly, but I'm not sure I had to >> > touch the huge page code at all. I have test code to ensure that it works the >> > same as with small pages, but everything worked pretty naturally. > Yeah, so the reason I'm asking about expectations is that this code: > > + follow_ret = follow_pte(tsk->mm, address, &ptep, &ptl); > + if (!follow_ret) { > + /* > + * On a successful follow, make sure to > + * drop the lock. > + */ > + pte = *ptep; > + pte_unmap_unlock(ptep, ptl); > + ret = pte_pkey(pte); > > is visibly hugepage-unsafe: if a vma is hugepage mapped, there are no ptes, only > pmds - and the protection key index lives in the pmd. We don't seem to recover > that information properly. You got me on this one. I assumed that follow_pte() handled huge pages. It does not. But, the code still worked. Since follow_pte() fails for all huge pages, it just falls back to pulling the protection key out of the VMA, which _does_ work for huge pages. I've actually removed the PTE walking and I just now use the VMA directly. I don't see a ton of additional value from walking the page tables when we can get what we need from the VMA. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org