[PATCH v14 00/39] arm64/sme: Initial support for the Scalable Matrix Extension

Mark Brown
2022-04-19T11:24:29Z

This series provides initial support for the ARMv9 Scalable Matrix
Extension (SME). SME takes the approach used for vectors in SVE and
extends this to provide architectural support for matrix operations. A
more detailed overview can be found in [1].

For the kernel SME can be thought of as a series of features which are
intended to be used together by applications but operate mostly
orthogonally:

- The ZA matrix register.
- Streaming mode, in which ZA can be accessed and a subset of SVE
features are available.
- A second vector length, used for streaming mode SVE and ZA and
controlled using a similar interface to that for SVE.
- TPIDR2, a new userspace controllable system register intended for use
by the C library for storing context related to the ZA ABI.

A substantial part of the series is dedicated to refactoring the
existing SVE support so that we don't need to duplicate code for
handling vector lengths and the SVE registers, this involves creating an
array of vector types and making the users take the vector type as a
parameter. I'm not 100% happy with this but wasn't able to come up with
anything better, duplicating code definitely felt like a bad idea so
this felt like the least bad thing. If this approach makes sense to
people it might make sense to split this off into a separate series
and/or merge it while the rest is pending review to try to make things a
little more digestable, the series is very large so it'd probably make
things easier to digest if some of the preparatory refactoring could be
merged before the rest is ready.

One feature of the architecture of particular note is that switching
to and from streaming mode may change the size of and invalidate the
contents of the SVE registers, and when in streaming mode the FFR is not
accessible. This complicates aspects of the ABI like signal handling
and ptrace.

This initial implementation is mainly intended to get the ABI in place,
there are several areas which will be worked on going forwards - some of
these will be blockers, others could be handled in followup serieses:

- SME is currently not supported for KVM guests, this will be done as a
followup series. A host system can use SME and run KVM guests but
SME is not available in the guests.
- The KVM host support is done in a very simplistic way, were anyone to
attempt to use it in production there would be performance impacts on
hosts with SME support. As part of this we also add enumeration of
fine grained traps.
- There is not currently ptrace or signal support TPIDR2, this will be
done as a followup series.
- No support is currently provided for scheduler control of SME or SME
applications, given the size of the SME register state the context
switch overhead may be noticable so this may be needed especially for
real time applications. Similar concerns already exist for larger
SVE vector lengths but are amplified for SME, particularly as the
vector length increases.
- There has been no work on optimising the performance of anything the
kernel does.

It is not expected that any systems will be encountered that support SME
but not SVE, SME is an ARMv9 feature and SVE is mandatory for ARMv9.
The code attempts to handle any such systems that are encountered but
this hasn't been tested extensively.

v14:
- Rebase onto v5.18-rc3.
v13:
- Preserve ZA in both parent and child on clone() and add a test case
for this.
- Fix EFI integration for FA64.
- Minor tweaks to the ABI document following Catlain's review.
- Add and make use of thread_get_cur_vl() helper.
- Fix some issues with SVE/FPSIMD register type moves in streaming SVE
ptrace.
- Typo fixes.
- Roll in separately posted series extending ptrace coverage in
kselftest for better integrated testing of the series.
v12:
- Fix some typos in the ABI document.
- Print a message when we skip a vector length in the signal tests.
- Add note of earliest toolchain versions with SME to manual encodings
for future reference now that's landed.
- Drop reference to PCS in sme.rst, it's not referenced and one of the
links was broken.
- Encode smstop and smstart as sysregs in the kernel.
- Don't redundantly flush the SVE register state when loading FPSIMD
state with SME enabled for the task, the architecture will do this
for us.
- Introduce and use task_get_cur_vl() to get the vector length for the
currently active SVE registers.
- Fix support for !FA64 mode in signal and syscall tests.
- Simplify instruction sequence for ssve_regs signal test.
- Actually include the ZA signal test in the patch set.
v11:
- Rebase onto v5.17-rc3.
- Provide a sme-inst.h to collect manual encodings in kselftest.
v10:
- Actually do the rebase of fixups from the previous version into
relevant patches.
v9:
- Remove defensive programming around IS_ENABLED() and FGT in KVM code.
- Fix naming of TPIDR2 FGT register bit.
- Add patches making handling of floating point register bits more
consistent (also sent as separate series).
- Drop now unused enumeration of fine grained traps.
v8:
- Rebase onto v5.17-rc1.
- Support interoperation with KVM, SME is disabled for KVM guests with
minimal handling for cleaning up SME state when entering and leaving
the guest.
- Document and implement that signal handlers are invoked with ZA and
streaming mode disabled.
- Use the RDSVL instruction introduced in EAC2 of the architecture to
obtain the streaming mode vector length during enumeration, ZA state
loading/saving and in test programs.
- Store a pointer to SVCR in fpsimd_last_state and use it in fpsimd_save()
for interoperation with KVM.
- Add a test case sme_trap_no_sm checking that we generate a SIGILL
when using an instruction that requires streaming mode without
enabling it.
- Add basic ZA context form validation to testcases helper library.
- Move signal tests over to validating streaming VL from ZA information.
- Pulled in patch removing ARRAY_SIZE() so that kselftest builds
cleanly and to avoid trivial conflicts.
v7:
- Rebase onto v5.16-rc3.
- Reduce indentation when supporting custom triggers for signal tests
as suggested by Catalin.
- Change to specifying a width for all CPU features rather than adding
single bit specific infrastructure.
- Don't require zeroing of non-shared SVE state during syscalls.
v6:
- Rebase onto v5.16-rc1.
- Return to disabling TIF_SVE on kernel entry even if we have SME
state, this avoids the need for KVM to handle the case where TIF_SVE
is set on guest entry.
- Add syscall-abi.h to SME updates to syscall-abi, mistakenly omitted
from commit.
v5:
- Rebase onto currently merged SVE and kselftest patches.
- Add support for the FA64 option, introduced in the recently published
EAC1 update to the specification.
- Pull in test program for the syscall ABI previously sent separately
with some revisions and add coverage for the SME ABI.
- Fix checking for options with 1 bit fields in ID_AA64SMFR0_EL1.
- Minor fixes and clarifications to the ABI documentation.
v4:
- Rebase onto merged patches.
- Remove an uneeded NULL check in vec_proc_do_default_vl().
- Include patch to factor out utility routines in kselftests written in
assembler.
- Specify -ffreestanding when building TPIDR2 test.
v3:
- Skip FFR rather than predicate registers in sve_flush_live().
- Don't assume a bool is all zeros in sve_flush_live() as per AAPCS.
- Don't redundantly specify a zero index when clearing FFR.
v2:
- Fix several issues with !SME and !SVE configurations.
- Preserve TPIDR2 when creating a new thread/process unless
CLONE_SETTLS is set.
- Report traps due to using features in an invalid mode as SIGILL.
- Spell out streaming mode behaviour in SVE ABI documentation more
directly.
- Document TPIDR2 in the ABI document.
- Use SMSTART and SMSTOP rather than read/modify/write sequences.
- Rework logic for exiting streaming mode on syscall.
- Don't needlessly initialise SVCR on access trap.
- Always restore SME VL for userspace if SME traps are disabled.
- Only yield to encourage preemption every 128 iterations in za-test,
otherwise do a getpid(), and validate SVCR after syscall.
- Leave streaming mode disabled except when reading the vector length
in za-test, and disable ZA after detecting a mismatch.
- Add SME support to vlset.
- Clarifications and typo fixes in comments.
- Move sme_alloc() forward declaration back a patch.

[1] https://community.arm.com/developer/ip-products/processors/b/processors-ip-blog/posts/scalable-matrix-extension-armv9-a-architecture

Mark Brown (39):
kselftest/arm64: Fix comment for ptrace_sve_get_fpsimd_data()
kselftest/arm64: Remove assumption that tasks start FPSIMD only
kselftest/arm64: Validate setting via FPSIMD and read via SVE regsets
arm64/sme: Provide ABI documentation for SME
arm64/sme: System register and exception syndrome definitions
arm64/sme: Manually encode SME instructions
arm64/sme: Early CPU setup for SME
arm64/sme: Basic enumeration support
arm64/sme: Identify supported SME vector lengths at boot
arm64/sme: Implement sysctl to set the default vector length
arm64/sme: Implement vector length configuration prctl()s
arm64/sme: Implement support for TPIDR2
arm64/sme: Implement SVCR context switching
arm64/sme: Implement streaming SVE context switching
arm64/sme: Implement ZA context switching
arm64/sme: Implement traps and syscall handling for SME
arm64/sme: Disable ZA and streaming mode when handling signals
arm64/sme: Implement streaming SVE signal handling
arm64/sme: Implement ZA signal handling
arm64/sme: Implement ptrace support for streaming mode SVE registers
arm64/sme: Add ptrace support for ZA
arm64/sme: Disable streaming mode and ZA when flushing CPU state
arm64/sme: Save and restore streaming mode over EFI runtime calls
KVM: arm64: Hide SME system registers from guests
KVM: arm64: Trap SME usage in guest
KVM: arm64: Handle SME host state when running guests
arm64/sme: Provide Kconfig for SME
kselftest/arm64: Add manual encodings for SME instructions
kselftest/arm64: sme: Add SME support to vlset
kselftest/arm64: Add tests for TPIDR2
kselftest/arm64: Extend vector configuration API tests to cover SME
kselftest/arm64: sme: Provide streaming mode SVE stress test
kselftest/arm64: signal: Handle ZA signal context in core code
kselftest/arm64: Add stress test for SME ZA context switching
kselftest/arm64: signal: Add SME signal handling tests
kselftest/arm64: Add streaming SVE to SVE ptrace tests
kselftest/arm64: Add coverage for the ZA ptrace interface
kselftest/arm64: Add SME support to syscall ABI test
selftests/arm64: Add a testcase for handling of ZA on clone()

Documentation/arm64/elf_hwcaps.rst | 33 +
Documentation/arm64/index.rst | 1 +
Documentation/arm64/sme.rst | 428 +++++++++++++
Documentation/arm64/sve.rst | 70 ++-
arch/arm64/Kconfig | 11 +
arch/arm64/include/asm/cpu.h | 4 +
arch/arm64/include/asm/cpufeature.h | 24 +
arch/arm64/include/asm/el2_setup.h | 64 +-
arch/arm64/include/asm/esr.h | 13 +-
arch/arm64/include/asm/exception.h | 1 +
arch/arm64/include/asm/fpsimd.h | 123 +++-
arch/arm64/include/asm/fpsimdmacros.h | 87 +++
arch/arm64/include/asm/hwcap.h | 8 +
arch/arm64/include/asm/kvm_arm.h | 1 +
arch/arm64/include/asm/kvm_host.h | 4 +
arch/arm64/include/asm/processor.h | 26 +-
arch/arm64/include/asm/sysreg.h | 67 ++
arch/arm64/include/asm/thread_info.h | 2 +
arch/arm64/include/uapi/asm/hwcap.h | 8 +
arch/arm64/include/uapi/asm/ptrace.h | 69 ++-
arch/arm64/include/uapi/asm/sigcontext.h | 55 +-
arch/arm64/kernel/cpufeature.c | 106 ++++
arch/arm64/kernel/cpuinfo.c | 13 +
arch/arm64/kernel/entry-common.c | 11 +
arch/arm64/kernel/entry-fpsimd.S | 36 ++
arch/arm64/kernel/fpsimd.c | 585 ++++++++++++++++--
arch/arm64/kernel/process.c | 44 +-
arch/arm64/kernel/ptrace.c | 358 +++++++++--
arch/arm64/kernel/signal.c | 188 +++++-
arch/arm64/kernel/syscall.c | 29 +-
arch/arm64/kernel/traps.c | 1 +
arch/arm64/kvm/fpsimd.c | 43 +-
arch/arm64/kvm/hyp/nvhe/switch.c | 30 +
arch/arm64/kvm/hyp/vhe/switch.c | 11 +-
arch/arm64/kvm/sys_regs.c | 9 +-
arch/arm64/tools/cpucaps | 2 +
include/uapi/linux/elf.h | 2 +
include/uapi/linux/prctl.h | 9 +
kernel/sys.c | 12 +
tools/testing/selftests/arm64/abi/.gitignore | 1 +
tools/testing/selftests/arm64/abi/Makefile | 9 +-
.../selftests/arm64/abi/syscall-abi-asm.S | 79 ++-
.../testing/selftests/arm64/abi/syscall-abi.c | 204 +++++-
.../testing/selftests/arm64/abi/syscall-abi.h | 15 +
tools/testing/selftests/arm64/abi/tpidr2.c | 298 +++++++++
tools/testing/selftests/arm64/fp/.gitignore | 5 +
tools/testing/selftests/arm64/fp/Makefile | 19 +-
tools/testing/selftests/arm64/fp/rdvl-sme.c | 14 +
tools/testing/selftests/arm64/fp/rdvl.S | 10 +
tools/testing/selftests/arm64/fp/rdvl.h | 1 +
tools/testing/selftests/arm64/fp/sme-inst.h | 51 ++
tools/testing/selftests/arm64/fp/ssve-stress | 59 ++
tools/testing/selftests/arm64/fp/sve-ptrace.c | 175 +++++-
tools/testing/selftests/arm64/fp/sve-test.S | 20 +
tools/testing/selftests/arm64/fp/vec-syscfg.c | 10 +
tools/testing/selftests/arm64/fp/vlset.c | 10 +-
.../testing/selftests/arm64/fp/za-fork-asm.S | 61 ++
tools/testing/selftests/arm64/fp/za-fork.c | 156 +++++
tools/testing/selftests/arm64/fp/za-ptrace.c | 356 +++++++++++
tools/testing/selftests/arm64/fp/za-stress | 59 ++
tools/testing/selftests/arm64/fp/za-test.S | 388 ++++++++++++
.../testing/selftests/arm64/signal/.gitignore | 3 +
.../selftests/arm64/signal/test_signals.h | 4 +
.../arm64/signal/test_signals_utils.c | 6 +
.../testcases/fake_sigreturn_sme_change_vl.c | 92 +++
.../arm64/signal/testcases/sme_trap_no_sm.c | 38 ++
.../signal/testcases/sme_trap_non_streaming.c | 45 ++
.../arm64/signal/testcases/sme_trap_za.c | 36 ++
.../selftests/arm64/signal/testcases/sme_vl.c | 68 ++
.../arm64/signal/testcases/ssve_regs.c | 135 ++++
.../arm64/signal/testcases/testcases.c | 36 ++
.../arm64/signal/testcases/testcases.h | 3 +-
.../arm64/signal/testcases/za_regs.c | 128 ++++
73 files changed, 4991 insertions(+), 191 deletions(-)
create mode 100644 Documentation/arm64/sme.rst
create mode 100644 tools/testing/selftests/arm64/abi/syscall-abi.h
create mode 100644 tools/testing/selftests/arm64/abi/tpidr2.c
create mode 100644 tools/testing/selftests/arm64/fp/rdvl-sme.c
create mode 100644 tools/testing/selftests/arm64/fp/sme-inst.h
create mode 100644 tools/testing/selftests/arm64/fp/ssve-stress
create mode 100644 tools/testing/selftests/arm64/fp/za-fork-asm.S
create mode 100644 tools/testing/selftests/arm64/fp/za-fork.c
create mode 100644 tools/testing/selftests/arm64/fp/za-ptrace.c
create mode 100644 tools/testing/selftests/arm64/fp/za-stress
create mode 100644 tools/testing/selftests/arm64/fp/za-test.S
create mode 100644 tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_sme_change_vl.c
create mode 100644 tools/testing/selftests/arm64/signal/testcases/sme_trap_no_sm.c
create mode 100644 tools/testing/selftests/arm64/signal/testcases/sme_trap_non_streaming.c
create mode 100644 tools/testing/selftests/arm64/signal/testcases/sme_trap_za.c
create mode 100644 tools/testing/selftests/arm64/signal/testcases/sme_vl.c
create mode 100644 tools/testing/selftests/arm64/signal/testcases/ssve_regs.c
create mode 100644 tools/testing/selftests/arm64/signal/testcases/za_regs.c

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2.30.2