Re: [PATCH] mm/userfaultfd: fix memory corruption due to writeprotect
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| From: | Nadav Amit <nadav.amit-AT-gmail.com> | |
| To: | Will Deacon <will-AT-kernel.org> | |
| Subject: | Re: [PATCH] mm/userfaultfd: fix memory corruption due to writeprotect | |
| Date: | Tue, 12 Jan 2021 14:29:51 -0800 | |
| Message-ID: | <F33D2DD9-97D5-44A0-890B-35FE686E36DC@gmail.com> | |
| Cc: | Yu Zhao <yuzhao-AT-google.com>, Laurent Dufour <ldufour-AT-linux.vnet.ibm.com>, Peter Zijlstra <peterz-AT-infradead.org>, Vinayak Menon <vinmenon-AT-codeaurora.org>, Linus Torvalds <torvalds-AT-linux-foundation.org>, Andy Lutomirski <luto-AT-kernel.org>, Peter Xu <peterx-AT-redhat.com>, Andrea Arcangeli <aarcange-AT-redhat.com>, linux-mm <linux-mm-AT-kvack.org>, lkml <linux-kernel-AT-vger.kernel.org>, Pavel Emelyanov <xemul-AT-openvz.org>, Mike Kravetz <mike.kravetz-AT-oracle.com>, Mike Rapoport <rppt-AT-linux.vnet.ibm.com>, stable <stable-AT-vger.kernel.org>, Minchan Kim <minchan-AT-kernel.org>, surenb-AT-google.com |
> On Jan 12, 2021, at 1:43 PM, Will Deacon <will@kernel.org> wrote: > > On Tue, Jan 12, 2021 at 12:38:34PM -0800, Nadav Amit wrote: >>> On Jan 12, 2021, at 11:56 AM, Yu Zhao <yuzhao@google.com> wrote: >>> On Tue, Jan 12, 2021 at 11:15:43AM -0800, Nadav Amit wrote: >>>> I will send an RFC soon for per-table deferred TLB flushes tracking. >>>> The basic idea is to save a generation in the page-struct that tracks >>>> when deferred PTE change took place, and track whenever a TLB flush >>>> completed. In addition, other users - such as mprotect - would use >>>> the tlb_gather interface. >>>> >>>> Unfortunately, due to limited space in page-struct this would only >>>> be possible for 64-bit (and my implementation is only for x86-64). >>> >>> I don't want to discourage you but I don't think this would end up >>> well. PPC doesn't necessarily follow one-page-struct-per-table rule, >>> and I've run into problems with this before while trying to do >>> something similar. >> >> Discourage, discourage. Better now than later. >> >> It will be relatively easy to extend the scheme to be per-VMA instead of >> per-table for architectures that prefer it this way. It does require >> TLB-generation tracking though, which Andy only implemented for x86, so I >> will focus on x86-64 right now. > > Can you remind me of what we're missing on arm64 in this area, please? I'm > happy to help get this up and running once you have something I can build > on. Let me first finish making something that we can use as a basis for a discussion. I do not waste your time before I have something ready.