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Pach series "Add FOLL_LONGTERM to GUP fast and use it".
HFI1, qib, and mthca, use get_user_pages_fast() due to its performance
advantages. These pages can be held for a significant time. But
get_user_pages_fast() does not protect against mapping FS DAX pages.
Introduce FOLL_LONGTERM and use this flag in get_user_pages_fast() which
retains the performance while also adding the FS DAX checks. XDP has also
shown interest in using this functionality.[1]
In addition we change get_user_pages() to use the new FOLL_LONGTERM flag
and remove the specialized get_user_pages_longterm call.
[1] https://lkml.org/lkml/2019/3/19/939
"longterm" is a relative thing and at this point is probably a misnomer.
This is really flagging a pin which is going to be given to hardware and
can't move. I've thought of a couple of alternative names but I think we
have to settle on if we are going to use FL_LAYOUT or something else to
solve the "longterm" problem. Then I think we can change the flag to a
better name.
Secondly, it depends on how often you are registering memory. I have
spoken with some RDMA users who consider MR in the performance path...
For the overall application performance. I don't have the numbers as the
tests for HFI1 were done a long time ago. But there was a significant
advantage. Some of which is probably due to the fact that you don't have
to hold mmap_sem.
Finally, architecturally I think it would be good for everyone to use
*_fast. There are patches submitted to the RDMA list which would allow
the use of *_fast (they reworking the use of mmap_sem) and as soon as they
are accepted I'll submit a patch to convert the RDMA core as well. Also
to this point others are looking to use *_fast.
As an aside, Jasons pointed out in my previous submission that *_fast and
*_unlocked look very much the same. I agree and I think further cleanup
will be coming. But I'm focused on getting the final solution for DAX at
the moment.
This patch (of 7):
This patch starts a series which aims to support FOLL_LONGTERM in
get_user_pages_fast(). Some callers who would like to do a longterm (user
controlled pin) of pages with the fast variant of GUP for performance
purposes.
Rather than have a separate get_user_pages_longterm() call, introduce
FOLL_LONGTERM and change the longterm callers to use it.
This patch does not change any functionality. In the short term
"longterm" or user controlled pins are unsafe for Filesystems and FS DAX
in particular has been blocked. However, callers of get_user_pages_fast()
were not "protected".
FOLL_LONGTERM can _only_ be supported with get_user_pages[_fast]() as it
requires vmas to determine if DAX is in use.
NOTE: In merging with the CMA changes we opt to change the
get_user_pages() call in check_and_migrate_cma_pages() to a call of
__get_user_pages_locked() on the newly migrated pages. This makes the
code read better in that we are calling __get_user_pages_locked() on the
pages before and after a potential migration.
As a side affect some of the interfaces are cleaned up but this is not the
primary purpose of the series.
In review[1] it was asked:
<quote>
> This I don't get - if you do lock down long term mappings performance
> of the actual get_user_pages call shouldn't matter to start with.
>
> What do I miss?
A couple of points.
First "longterm" is a relative thing and at this point is probably a
misnomer. This is really flagging a pin which is going to be given to
hardware and can't move. I've thought of a couple of alternative names
but I think we have to settle on if we are going to use FL_LAYOUT or
something else to solve the "longterm" problem. Then I think we can
change the flag to a better name.
Second, It depends on how often you are registering memory. I have spoken
with some RDMA users who consider MR in the performance path... For the
overall application performance. I don't have the numbers as the tests
for HFI1 were done a long time ago. But there was a significant
advantage. Some of which is probably due to the fact that you don't have
to hold mmap_sem.
Finally, architecturally I think it would be good for everyone to use
*_fast. There are patches submitted to the RDMA list which would allow
the use of *_fast (they reworking the use of mmap_sem) and as soon as they
are accepted I'll submit a patch to convert the RDMA core as well. Also
to this point others are looking to use *_fast.
As an asside, Jasons pointed out in my previous submission that *_fast and
*_unlocked look very much the same. I agree and I think further cleanup
will be coming. But I'm focused on getting the final solution for DAX at
the moment.
</quote>
[1] https://lore.kernel.org/lkml/20190220180255.GA12020@iweiny-DESK2.sc.intel.com/T/#md6abad2569f3bf6c1f03686c8097ab6563e94965
[ira.weiny@intel.com: v3]
Link: http://lkml.kernel.org/r/20190328084422.29911-2-ira.weiny@intel.com
Link: http://lkml.kernel.org/r/20190328084422.29911-2-ira.weiny@intel.com
Link: http://lkml.kernel.org/r/20190317183438.2057-2-ira.weiny@intel.com
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Rich Felker <dalias@libc.org>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Mike Marshall <hubcap@omnibond.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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ssh://gitolite.kernel.org/pub/scm/linux/kernel/git/powerpc/linux
Pull powerpc updates from Michael Ellerman:
"Slightly delayed due to the issue with printk() calling
probe_kernel_read() interacting with our new user access prevention
stuff, but all fixed now.
The only out-of-area changes are the addition of a cpuhp_state, small
additions to Documentation and MAINTAINERS updates.
Highlights:
- Support for Kernel Userspace Access/Execution Prevention (like
SMAP/SMEP/PAN/PXN) on some 64-bit and 32-bit CPUs. This prevents
the kernel from accidentally accessing userspace outside
copy_to/from_user(), or ever executing userspace.
- KASAN support on 32-bit.
- Rework of where we map the kernel, vmalloc, etc. on 64-bit hash to
use the same address ranges we use with the Radix MMU.
- A rewrite into C of large parts of our idle handling code for
64-bit Book3S (ie. power8 & power9).
- A fast path entry for syscalls on 32-bit CPUs, for a 12-17% speedup
in the null_syscall benchmark.
- On 64-bit bare metal we have support for recovering from errors
with the time base (our clocksource), however if that fails
currently we hang in __delay() and never crash. We now have support
for detecting that case and short circuiting __delay() so we at
least panic() and reboot.
- Add support for optionally enabling the DAWR on Power9, which had
to be disabled by default due to a hardware erratum. This has the
effect of enabling hardware breakpoints for GDB, the downside is a
badly behaved program could crash the machine by pointing the DAWR
at cache inhibited memory. This is opt-in obviously.
- xmon, our crash handler, gets support for a read only mode where
operations that could change memory or otherwise disturb the system
are disabled.
Plus many clean-ups, reworks and minor fixes etc.
Thanks to: Christophe Leroy, Akshay Adiga, Alastair D'Silva, Alexey
Kardashevskiy, Andrew Donnellan, Aneesh Kumar K.V, Anju T Sudhakar,
Anton Blanchard, Ben Hutchings, Bo YU, Breno Leitao, Cédric Le Goater,
Christopher M. Riedl, Christoph Hellwig, Colin Ian King, David Gibson,
Ganesh Goudar, Gautham R. Shenoy, George Spelvin, Greg Kroah-Hartman,
Greg Kurz, Horia Geantă, Jagadeesh Pagadala, Joel Stanley, Joe
Perches, Julia Lawall, Laurentiu Tudor, Laurent Vivier, Lukas Bulwahn,
Madhavan Srinivasan, Mahesh Salgaonkar, Mathieu Malaterre, Michael
Neuling, Mukesh Ojha, Nathan Fontenot, Nathan Lynch, Nicholas Piggin,
Nick Desaulniers, Oliver O'Halloran, Peng Hao, Qian Cai, Ravi
Bangoria, Rick Lindsley, Russell Currey, Sachin Sant, Stewart Smith,
Sukadev Bhattiprolu, Thomas Huth, Tobin C. Harding, Tyrel Datwyler,
Valentin Schneider, Wei Yongjun, Wen Yang, YueHaibing"
* tag 'powerpc-5.2-1' of ssh://gitolite.kernel.org/pub/scm/linux/kernel/git/powerpc/linux: (205 commits)
powerpc/64s: Use early_mmu_has_feature() in set_kuap()
powerpc/book3s/64: check for NULL pointer in pgd_alloc()
powerpc/mm: Fix hugetlb page initialization
ocxl: Fix return value check in afu_ioctl()
powerpc/mm: fix section mismatch for setup_kup()
powerpc/mm: fix redundant inclusion of pgtable-frag.o in Makefile
powerpc/mm: Fix makefile for KASAN
powerpc/kasan: add missing/lost Makefile
selftests/powerpc: Add a signal fuzzer selftest
powerpc/booke64: set RI in default MSR
ocxl: Provide global MMIO accessors for external drivers
ocxl: move event_fd handling to frontend
ocxl: afu_irq only deals with IRQ IDs, not offsets
ocxl: Allow external drivers to use OpenCAPI contexts
ocxl: Create a clear delineation between ocxl backend & frontend
ocxl: Don't pass pci_dev around
ocxl: Split pci.c
ocxl: Remove some unused exported symbols
ocxl: Remove superfluous 'extern' from headers
ocxl: read_pasid never returns an error, so make it void
...
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