[PATCH v2 00/28] ARM Scalable Vector Extension (SVE)

Dave Martin
2017-08-31T17:00:32Z

This series implements Linux kernel support for the ARM Scalable Vector
Extension (SVE). [1] It supersedes the previous v1: see [3] for link.
See the individual patches for details of changes.

The patches apply on v4.13-rc7 + linux-arm64/for-next/core.
For convenience, a git tree is available. [4]

To reduce spam, some people may not been copied on the entire series.
For those who did not receive the whole series, it can be found in the
linux-arm-kernel archive. [2]

*Note* The final two patches (27-28) of the series are still RFC --
before committing to this ABI it would be good to get feedback on
whether the approach makes sense and whether it suitable for other
architectures. These two patches are not required by the rest of the
series and can be revised or merged later.

Support for use of SVE by KVM guests is not currently included.
Instead, such use will be trapped and reflected to the guest as
undefined instruction execution. SVE is hidden from the view of the
CPU feature registers visible to guests, so that guests will not
expect it to work.

This series has been build- and boot-tested on Juno r0 and the ARM FVP
Base model with SVE plugin. Because there is no hardware with SVE
support yet, testing of the SVE functionality has only been performed on
the model.

Regression testing of v1 using LTP showed no regressions on the kernel
tests.

Regression testing of v2 is under way.

Series summary:

* Patches 1-5 contain some individual bits of preparatory spadework,
which are indirectly related to SVE.

Dave Martin (5):
regset: Add support for dynamically sized regsets
arm64: KVM: Hide unsupported AArch64 CPU features from guests
arm64: efi: Add missing Kconfig dependency on KERNEL_MODE_NEON
arm64: Port deprecated instruction emulation to new sysctl interface
arm64: fpsimd: Simplify uses of {set,clear}_ti_thread_flag()

Non-trivial changes among these are:

* Patch 1: updates the regset core code to handle regsets whose size
is not fixed at compile time. This avoids bloating coredumps even
though the maximum theoretical SVE regset size is large.

* Patch 2: extends KVM to modify the ARM architectural ID registers
seen by guests, by trapping and emulating certain registers. For
SVE this is a temporary measure, but it may be useful for other
architecture extensions. This patch may also be built on in the
future, since the only registers currently emulated are those
required for hiding SVE.

* Patches 6-10 add SVE-specific system register and structure layout
definitions, and the low-level boot code and accessors needed for
making use of SVE.

Dave Martin (5):
arm64/sve: System register and exception syndrome definitions
arm64/sve: Low-level SVE architectural state manipulation functions
arm64/sve: Kconfig update and conditional compilation support
arm64/sve: Signal frame and context structure definition
arm64/sve: Low-level CPU setup

* Patches 11-13 implement the core context management facilities to
provide each user task with its own SVE register context, signal
handling facilities, and sane programmer's model interoperation
between SVE and FPSIMD.

Dave Martin (3):
arm64/sve: Core task context handling
arm64/sve: Support vector length resetting for new processes
arm64/sve: Signal handling support

* Patches 14 and 16 provide backend logic for detecting and making use
of the different SVE vector lengths supported by the hardware.

* Patch 15 moves around code in cpufeatures.c to fit.

Dave Martin (3):
arm64/sve: Backend logic for setting the vector length
arm64: cpufeature: Move sys_caps_initialised declarations
arm64/sve: Probe SVE capabilities and usable vector lengths

* Patches 17-18 update the kernel-mode NEON / EFI FPSIMD frameworks to
interoperate correctly with SVE.

Dave Martin (2):
arm64/sve: Preserve SVE registers around kernel-mode NEON use
arm64/sve: Preserve SVE registers around EFI runtime service calls

* Patches 19-21 implement the userspace frontend for managing SVE,
comprising ptrace, some new arch-specific prctl() calls, and a new
sysctl for init-time setup.

Dave Martin (3):
arm64/sve: ptrace and ELF coredump support
arm64/sve: Add prctl controls for userspace vector length management
arm64/sve: Add sysctl to set the default vector length for new
processes

* Patches 22-24 provide stub KVM extensions for using KVM only on the
host, while denying guest access. (A future series will extend this
with full support for SVE in guests.)

Dave Martin (3):
arm64/sve: KVM: Prevent guests from using SVE
arm64/sve: KVM: Treat guest SVE use as undefined instruction
execution
arm64/sve: KVM: Hide SVE from CPU features exposed to guests

And finally:

* Patch 25 disengages the safety catch, enabling the kernel SVE runtime
support and allowing userspace to use SVE.

Dave Martin (1):
arm64/sve: Detect SVE and activate runtime support

* Patch 26 adds some basic documentation.

Dave Martin (1):
arm64/sve: Add documentation

* Patches 27-28 (which may be considered RFC) propose a mechanism to
report the maximum runtime signal frame size to userspace.

Dave Martin (2):
arm64: signal: Report signal frame size to userspace via auxv
arm64/sve: signal: Include SVE when computing AT_MINSIGSTKSZ

References:

[1] ARM Scalable Vector Extension
https://community.arm.com/groups/processors/blog/2016/08/22/technology-update-the-scalable-vector-extension-sve-for-the-armv8-a-architecture

[2] linux-arm-kernel August 2017 Archives by thread
http://lists.infradead.org/pipermail/linux-arm-kernel/2017-August/thread.html

[3] [PATCH 00/27] ARM Scalable Vector Extension (SVE)
http://lists.infradead.org/pipermail/linux-arm-kernel/2017-August/524691.html

[4] http://linux-arm.org/git?p=linux-dm.git;a=shortlog;h=refs/heads/sve/v2
git://linux-arm.org/linux-dm.git sve/v2

Full series and diffstat:

Dave Martin (28):
regset: Add support for dynamically sized regsets
arm64: KVM: Hide unsupported AArch64 CPU features from guests
arm64: efi: Add missing Kconfig dependency on KERNEL_MODE_NEON
arm64: Port deprecated instruction emulation to new sysctl interface
arm64: fpsimd: Simplify uses of {set,clear}_ti_thread_flag()
arm64/sve: System register and exception syndrome definitions
arm64/sve: Low-level SVE architectural state manipulation functions
arm64/sve: Kconfig update and conditional compilation support
arm64/sve: Signal frame and context structure definition
arm64/sve: Low-level CPU setup
arm64/sve: Core task context handling
arm64/sve: Support vector length resetting for new processes
arm64/sve: Signal handling support
arm64/sve: Backend logic for setting the vector length
arm64: cpufeature: Move sys_caps_initialised declarations
arm64/sve: Probe SVE capabilities and usable vector lengths
arm64/sve: Preserve SVE registers around kernel-mode NEON use
arm64/sve: Preserve SVE registers around EFI runtime service calls
arm64/sve: ptrace and ELF coredump support
arm64/sve: Add prctl controls for userspace vector length management
arm64/sve: Add sysctl to set the default vector length for new
processes
arm64/sve: KVM: Prevent guests from using SVE
arm64/sve: KVM: Treat guest SVE use as undefined instruction execution
arm64/sve: KVM: Hide SVE from CPU features exposed to guests
arm64/sve: Detect SVE and activate runtime support
arm64/sve: Add documentation
arm64: signal: Report signal frame size to userspace via auxv
arm64/sve: signal: Include SVE when computing AT_MINSIGSTKSZ

Documentation/arm64/cpu-feature-registers.txt | 6 +-
Documentation/arm64/sve.txt | 477 +++++++++++++++++
arch/arm/include/asm/kvm_host.h | 3 +
arch/arm64/Kconfig | 12 +
arch/arm64/include/asm/cpu.h | 4 +
arch/arm64/include/asm/cpucaps.h | 3 +-
arch/arm64/include/asm/cpufeature.h | 35 ++
arch/arm64/include/asm/elf.h | 5 +
arch/arm64/include/asm/esr.h | 3 +-
arch/arm64/include/asm/fpsimd.h | 71 ++-
arch/arm64/include/asm/fpsimdmacros.h | 148 ++++++
arch/arm64/include/asm/kvm_arm.h | 5 +-
arch/arm64/include/asm/kvm_host.h | 11 +
arch/arm64/include/asm/processor.h | 10 +
arch/arm64/include/asm/sysreg.h | 24 +
arch/arm64/include/asm/thread_info.h | 2 +
arch/arm64/include/asm/traps.h | 2 +
arch/arm64/include/uapi/asm/auxvec.h | 3 +-
arch/arm64/include/uapi/asm/hwcap.h | 1 +
arch/arm64/include/uapi/asm/ptrace.h | 135 +++++
arch/arm64/include/uapi/asm/sigcontext.h | 120 ++++-
arch/arm64/kernel/armv8_deprecated.c | 15 +-
arch/arm64/kernel/cpufeature.c | 96 +++-
arch/arm64/kernel/cpuinfo.c | 7 +
arch/arm64/kernel/entry-fpsimd.S | 17 +
arch/arm64/kernel/entry.S | 14 +-
arch/arm64/kernel/fpsimd.c | 729 +++++++++++++++++++++++++-
arch/arm64/kernel/head.S | 13 +-
arch/arm64/kernel/process.c | 4 +
arch/arm64/kernel/ptrace.c | 270 +++++++++-
arch/arm64/kernel/signal.c | 222 +++++++-
arch/arm64/kernel/signal32.c | 2 +-
arch/arm64/kernel/traps.c | 5 +-
arch/arm64/kvm/handle_exit.c | 8 +
arch/arm64/kvm/hyp/switch.c | 12 +-
arch/arm64/kvm/sys_regs.c | 292 +++++++++--
arch/arm64/mm/proc.S | 14 +-
fs/binfmt_elf.c | 6 +-
include/linux/regset.h | 67 ++-
include/uapi/linux/elf.h | 1 +
include/uapi/linux/prctl.h | 9 +
kernel/sys.c | 12 +
virt/kvm/arm/arm.c | 3 +
43 files changed, 2753 insertions(+), 145 deletions(-)
create mode 100644 Documentation/arm64/sve.txt

--
2.1.4