From: Peter Xu <peterx@redhat.com>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Mike Kravetz <mike.kravetz@oracle.com>,
Nadav Amit <nadav.amit@gmail.com>,
Matthew Wilcox <willy@infradead.org>,
Mike Rapoport <rppt@linux.vnet.ibm.com>,
David Hildenbrand <david@redhat.com>,
Hugh Dickins <hughd@google.com>,
Jerome Glisse <jglisse@redhat.com>,
"Kirill A . Shutemov" <kirill@shutemov.name>,
Andrea Arcangeli <aarcange@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
Axel Rasmussen <axelrasmussen@google.com>,
Alistair Popple <apopple@nvidia.com>
Subject: Re: [PATCH v8 22/23] mm: Enable PTE markers by default
Date: Tue, 19 Apr 2022 18:01:14 -0400 [thread overview]
Message-ID: <Yl8xKh9Dc+nPr30a@xz-m1.local> (raw)
In-Reply-To: <Yl8ojDwxsD/wqWM4@cmpxchg.org>
On Tue, Apr 19, 2022 at 05:24:28PM -0400, Johannes Weiner wrote:
> On Tue, Apr 19, 2022 at 04:28:16PM -0400, Peter Xu wrote:
> > On Tue, Apr 19, 2022 at 04:14:11PM -0400, Johannes Weiner wrote:
> > > On Tue, Apr 19, 2022 at 03:59:21PM -0400, Peter Xu wrote:
> > > > @@ -910,16 +910,16 @@ config ANON_VMA_NAME
> > > Btw, this doesn't do much without userfaultfd being enabled in
> > > general, right?
> >
> > So far yes, but I'm thinking there can be potential other users of
> > PTE_MARKERS from mm world. The most close discussion is on the swap read
> > failures and this patch proposed by Miaohe:
> >
> > https://lore.kernel.org/lkml/20220416030549.60559-1-linmiaohe@huawei.com/
> >
> > So I hope we can still keep them around here under mm/ if possible, and
> > from the gut feeling it really should..
>
> Agreed, mm/ seems a good fit for PTE_MARKER.
>
> If it's invisible and gets selected as needed, it's less of a concern,
> IMO. I'm somewhat worried about when and how the user-visible options
> show up right now, though...
>
> > > Would it make sense to have it next to 'config USERFAULTFD' as a
> > > sub-option?
> >
> > Yes another good question. :)
> >
> > IIUC CONFIG_USERFAULTFD resides in init/Kconfig because it introduces a new
> > syscall. Same to the rest of the bits for uffd since then, namely:
> >
> > - USERFAULTFD_WP
> > - USERFAULTFD_MINOR
> >
> > What I am thinking now is the other way round of your suggestion: whether
> > we should move most of them out, at least the _WP and _MINOR configs into
> > mm/? Because IMHO they are really pure mm ideas and they're irrelevant to
> > syscalls and init.
>
> I'm thinking the MM submenu would probably be a better fit for all
> user-visible userfaultfd options, including the syscall. Like you say,
> it's an MM concept.
>
> But if moving the syscall knob out from init isn't popular, IMO it
> would be better to add the new WP option to init as well. This ensures
> that when somebody selects userfaultfd, they also see the relevant
> suboptions and don't have to chase them down across multiple submenus.
>
> Conversely, they should also have the necessary depend clauses so that
> suboptions aren't visible without the main feature. E.g. it asked me
> for userfaultd options even though I have CONFIG_USERFAULTFD=n.
Hmm, this is a bit weird... since we do have that dependency chain for
PTE_MARKER_UFFD_WP -> HAVE_ARCH_USERFAULTFD_WP -> USERFAULTFD:
in arch/x86/Kconfig:
config X86
...
select HAVE_ARCH_USERFAULTFD_WP if X86_64 && USERFAULTFD
in mm/Kconfig (with/without the "mm/uffd: Hide PTE_MARKER" patch applied):
config PTE_MARKER_UFFD_WP
...
depends on HAVE_ARCH_USERFAULTFD_WP
So logically if !USERFAULTFD we shouldn't see PTE_MARKER_UFFD_WP at all?
That's also what I got when I tried it out for either !USERFAULTFD on x86,
or any non-x86 platforms (because there we have !HAVE_ARCH_USERFAULTFD_WP
constantly irrelevant of USERFAULTFD). Though I could have missed
something..
>
> What do you think?
I don't have a strong preference here, I think it's okay if it's preferred
that we only put user-visible configs into mm/Kconfig. It's just that I
see we have tons of user-invisible configs already in mm/Kconfig, to list
some:
config ARCH_HAS_HUGEPD
config MAPPING_DIRTY_HELPERS
config KMAP_LOCAL
config KMAP_LOCAL_NON_LINEAR_PTE_ARRAY
But I'm not sure whether it's a rule of thumb somewhere else.
At the meantime, I also looked at whether syscall configs are always and
only be put under init/, and funnily I got:
$ find . -name Kconfig | xargs grep --color -E "\".*syscall.*\""
./init/Kconfig: bool "Enable process_vm_readv/writev syscalls"
./init/Kconfig: bool "uselib syscall"
./init/Kconfig: bool "sgetmask/ssetmask syscalls support" if EXPERT
./init/Kconfig: bool "Sysfs syscall support" if EXPERT
./init/Kconfig: bool "open by fhandle syscalls" if EXPERT
./init/Kconfig: bool "Enable madvise/fadvise syscalls" if EXPERT
./arch/xtensa/Kconfig: bool "Enable fast atomic syscalls"
./arch/xtensa/Kconfig: bool "Enable spill registers syscall"
./arch/powerpc/Kconfig: bool "Support setting protections for 4k subpages (subpage_prot syscall)"
./arch/powerpc/Kconfig: bool "Enable filtering of RTAS syscalls"
./arch/Kconfig: bool "Support for randomizing kernel stack offset on syscall entry" if EXPERT
./arch/s390/Kconfig: bool "Verify kernel signature during kexec_file_load() syscall"
./arch/sh/mm/Kconfig: bool "Support vsyscall page"
./arch/x86/Kconfig: bool "Enable vsyscall emulation" if EXPERT
./arch/x86/Kconfig: bool "Verify kernel signature during kexec_file_load() syscall"
./arch/x86/Kconfig: bool "Require a valid signature in kexec_file_load() syscall"
./arch/x86/Kconfig: prompt "vsyscall table for legacy applications"
./arch/arm64/Kconfig: bool "Verify kernel signature during kexec_file_load() syscall"
./arch/arm64/Kconfig: bool "Enable the tagged user addresses syscall ABI"
./kernel/trace/Kconfig: bool "Trace syscalls"
./kernel/trace/Kconfig: bool "Run selftest on syscall events"
So let's put aside arch specific lines, ftrace does have FTRACE_SYSCALLS
that lies in the kernel/trace/ dir.. not sure whether we could move
USERFAULTFD and all the rest into mm/ as well? Or perhaps that's just a
bad example? :)
Thanks,
--
Peter Xu
next prev parent reply other threads:[~2022-04-19 22:01 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-05 1:46 [PATCH v8 00/23] userfaultfd-wp: Support shmem and hugetlbfs Peter Xu
2022-04-05 1:46 ` [PATCH v8 01/23] mm: Introduce PTE_MARKER swap entry Peter Xu
2022-04-12 1:07 ` Alistair Popple
2022-04-12 19:45 ` Peter Xu
2022-04-13 0:30 ` Alistair Popple
2022-04-13 13:44 ` Peter Xu
2022-04-19 8:25 ` Alistair Popple
2022-04-19 19:44 ` Peter Xu
2022-04-05 1:48 ` [PATCH v8 02/23] mm: Teach core mm about pte markers Peter Xu
2022-04-12 1:22 ` Alistair Popple
2022-04-12 19:53 ` Peter Xu
2022-04-05 1:48 ` [PATCH v8 03/23] mm: Check against orig_pte for finish_fault() Peter Xu
2022-04-12 2:05 ` Alistair Popple
2022-04-12 19:54 ` Peter Xu
[not found] ` <CGME20220413140330eucas1p167da41e079712b829ef8237dc27b049c@eucas1p1.samsung.com>
2022-04-13 14:03 ` Marek Szyprowski
2022-04-13 16:43 ` Peter Xu
2022-04-14 7:51 ` Marek Szyprowski
2022-04-14 16:30 ` Peter Xu
2022-04-14 20:57 ` Andrew Morton
2022-04-14 21:08 ` Peter Xu
2022-04-15 14:21 ` Guenter Roeck
2022-04-15 14:41 ` Peter Xu
2022-04-05 1:48 ` [PATCH v8 04/23] mm/uffd: PTE_MARKER_UFFD_WP Peter Xu
2022-04-06 1:41 ` kernel test robot
2022-04-05 1:48 ` [PATCH v8 05/23] mm/shmem: Take care of UFFDIO_COPY_MODE_WP Peter Xu
2022-04-05 1:48 ` [PATCH v8 06/23] mm/shmem: Handle uffd-wp special pte in page fault handler Peter Xu
2022-05-11 16:30 ` David Hildenbrand
2022-05-12 16:34 ` Peter Xu
2022-04-05 1:48 ` [PATCH v8 07/23] mm/shmem: Persist uffd-wp bit across zapping for file-backed Peter Xu
2022-04-05 1:48 ` [PATCH v8 08/23] mm/shmem: Allow uffd wr-protect none pte for file-backed mem Peter Xu
2022-04-05 1:48 ` [PATCH v8 09/23] mm/shmem: Allows file-back mem to be uffd wr-protected on thps Peter Xu
2022-04-05 1:48 ` [PATCH v8 10/23] mm/shmem: Handle uffd-wp during fork() Peter Xu
2022-04-06 6:16 ` kernel test robot
2022-04-06 12:18 ` Peter Xu
2022-04-05 1:48 ` [PATCH v8 11/23] mm/hugetlb: Introduce huge pte version of uffd-wp helpers Peter Xu
2022-04-05 1:49 ` [PATCH v8 12/23] mm/hugetlb: Hook page faults for uffd write protection Peter Xu
2022-04-05 1:49 ` [PATCH v8 13/23] mm/hugetlb: Take care of UFFDIO_COPY_MODE_WP Peter Xu
2022-04-05 1:49 ` [PATCH v8 14/23] mm/hugetlb: Handle UFFDIO_WRITEPROTECT Peter Xu
2022-04-05 1:49 ` [PATCH v8 15/23] mm/hugetlb: Handle pte markers in page faults Peter Xu
2022-04-06 13:37 ` kernel test robot
2022-04-06 15:02 ` Peter Xu
2022-04-05 1:49 ` [PATCH v8 16/23] mm/hugetlb: Allow uffd wr-protect none ptes Peter Xu
2022-04-05 1:49 ` [PATCH v8 17/23] mm/hugetlb: Only drop uffd-wp special pte if required Peter Xu
2022-04-05 1:49 ` [PATCH v8 18/23] mm/hugetlb: Handle uffd-wp during fork() Peter Xu
2022-04-05 1:49 ` [PATCH v8 19/23] mm/khugepaged: Don't recycle vma pgtable if uffd-wp registered Peter Xu
2022-04-05 1:49 ` [PATCH v8 20/23] mm/pagemap: Recognize uffd-wp bit for shmem/hugetlbfs Peter Xu
2022-04-05 1:49 ` [PATCH v8 21/23] mm/uffd: Enable write protection for shmem & hugetlbfs Peter Xu
2022-04-05 1:49 ` [PATCH v8 22/23] mm: Enable PTE markers by default Peter Xu
2022-04-19 15:13 ` Johannes Weiner
2022-04-19 19:59 ` Peter Xu
2022-04-19 20:14 ` Johannes Weiner
2022-04-19 20:28 ` Peter Xu
2022-04-19 21:24 ` Johannes Weiner
2022-04-19 22:01 ` Peter Xu [this message]
2022-04-20 13:46 ` Johannes Weiner
2022-04-20 14:25 ` Peter Xu
2022-04-05 1:49 ` [PATCH v8 23/23] selftests/uffd: Enable uffd-wp for shmem/hugetlbfs Peter Xu
2022-04-05 22:16 ` [PATCH v8 00/23] userfaultfd-wp: Support shmem and hugetlbfs Andrew Morton
2022-04-05 22:42 ` Peter Xu
2022-04-05 22:49 ` Andrew Morton
2022-04-05 23:02 ` Peter Xu
2022-04-05 23:08 ` Andrew Morton
2022-05-10 19:05 ` Andrew Morton
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