[PATCH v6 00/10] Improve signal performance on PPC64 with KUAP

[Christopher M. Riedl]

As reported by Anton, there is a large penalty to signal handling
performance on radix systems using KUAP. The signal handling code
performs many user access operations, each of which needs to switch the
KUAP permissions bit to open and then close user access. This involves a
costly 'mtspr' operation [0].

There is existing work done on x86 and by Christophe Leroy for PPC32 to
instead open up user access in "blocks" using user_*_access_{begin,end}.
We can do the same in PPC64 to bring performance back up on KUAP-enabled
radix and now also hash MMU systems [1].

Hash MMU KUAP support along with uaccess flush has landed in linuxppc/next
since the last revision. This series also provides a large benefit on hash
with KUAP. However, in the hash implementation of KUAP the user AMR is
always restored during system_call_exception() which cannot be avoided.
Fewer user access switches naturally also result in less uaccess flushing.

The first two patches add some needed 'unsafe' versions of copy-from
functions. While these do not make use of asm-goto they still allow for
avoiding the repeated uaccess switches.

The third patch moves functions called by setup_sigcontext() into a new
prepare_setup_sigcontext() to simplify converting setup_sigcontext()
into an 'unsafe' version which assumes an open uaccess window later.

The fourth and fifths patches clean-up some of the Transactional Memory
ifdef stuff to simplify using uaccess blocks later.

The next two patches rewrite some of the signal64 helper functions to
be 'unsafe'. Finally, the last three patches update the main signal
handling functions to make use of the new 'unsafe' helpers and eliminate
some additional uaccess switching.

I used the will-it-scale signal1 benchmark to measure and compare
performance [2]. The below results are from running a minimal
kernel+initramfs QEMU/KVM guest on a POWER9 Blackbird:

	signal1_threads -t1 -s10

	|                              | hash   | radix  |
	| ---------------------------- | ------ | ------ |
	| linuxppc/next                | 117288 | 135555 |
	| linuxppc/next w/o KUAP+KUEP  | 224759 | 227886 |
	| unsafe-signal64              | 197378 | 233528 |

[0]: https://github.com/linuxppc/issues/issues/277
[1]: https://patchwork.ozlabs.org/project/linuxppc-dev/list/?series=196278
[2]: https://github.com/antonblanchard/will-it-scale/blob/master/tests/signal1.c

v6:	* Rebase on latest linuxppc/next and address feedback comments from
	  Daniel Axtens and friends (also pick up some Reviewed-by tags)
	* Simplify __get_user_sigset(), fix sparse warnings, and use it
	  in ppc32 signal handling
	* Remove ctx_has_vsx_region arg to prepare_setup_sigcontext()
	* Remove local buffer in copy_{fpr,vsx}_from_user()
	* Rework the TM ifdefery-removal and remove one of the ifdef
	  pairs altogether

v5:	* Use sizeof(buf) in copy_{vsx,fpr}_from_user() (Thanks David Laight)
	* Rebase on latest linuxppc/next

v4:	* Fix issues identified by Christophe Leroy (Thanks for review)
	* Use __get_user() directly to copy the 8B sigset_t

v3:	* Rebase on latest linuxppc/next
	* Reword confusing commit messages
	* Add missing comma in macro in signal.h which broke compiles without
	  CONFIG_ALTIVEC
	* Validate hash KUAP signal performance improvements

v2:	* Rebase on latest linuxppc/next + Christophe Leroy's PPC32
	  signal series
	* Simplify/remove TM ifdefery similar to PPC32 series and clean
	  up the uaccess begin/end calls
	* Isolate non-inline functions so they are not called when
	  uaccess window is open

Christopher M. Riedl (8):
  powerpc/uaccess: Add unsafe_copy_from_user
  powerpc/signal: Add unsafe_copy_{vsx,fpr}_from_user()
  powerpc/signal64: Remove non-inline calls from setup_sigcontext()
  powerpc: Reference parameter in MSR_TM_ACTIVE() macro
  powerpc/signal64: Remove TM ifdefery in middle of if/else block
  powerpc/signal64: Replace setup_sigcontext() w/
    unsafe_setup_sigcontext()
  powerpc/signal64: Replace restore_sigcontext() w/
    unsafe_restore_sigcontext()
  powerpc/signal: Use __get_user() to copy sigset_t

Daniel Axtens (2):
  powerpc/signal64: Rewrite handle_rt_signal64() to minimise uaccess
    switches
  powerpc/signal64: Rewrite rt_sigreturn() to minimise uaccess switches

 arch/powerpc/include/asm/reg.h     |   2 +-
 arch/powerpc/include/asm/uaccess.h |   3 +
 arch/powerpc/kernel/process.c      |   3 +-
 arch/powerpc/kernel/signal.h       |  33 +++
 arch/powerpc/kernel/signal_32.c    |   2 +-
 arch/powerpc/kernel/signal_64.c    | 315 +++++++++++++++++------------
 6 files changed, 227 insertions(+), 131 deletions(-)

-- 
2.26.1