[0/4] arm64: pseudo-nmi: elide code when CONFIG_ARM64_PSEUDO_NMI=n

Message

Mark Rutland Jan. 23, 2023, 12:40 p.m. UTC

This series addresses a couple of sub-optimal code generation issues with
arm64's pseudo-nmi support code:

* Even when CONFIG_ARM64_PSEUDO_NMI=n, we generate alternative code
  sequences and alt_instr entries which will never be used. This series
  reworks the irqflags code to use alternative branches (with an
  IS_ENABLED() check), which allows the alternatives to be elided when
  CONFIG_ARM64_PSEUDO_NMI=n.

* When PMHE is eanbled in HW, we must synchronize PMR updates using a
  DSB SY. We take pains to avoid this using a static key to skip the
  barrier when PMHE is not in use, but this results in unnecessarily
  branchy code. This series replaces the static key with an alternative,
  allowing the DSB SY to be relaxed to a NOP.

These changes make a defconfig kernel a little smaller, and does not
adversely affect the size of a CONFIG_ARM64_PSEUDO_NMI=y kernel. The
structural changes will also make it easier for a subsequent series to
rework the irqflag and daifflag management, addressing some
long-standing edge cases and preparing for ARMv8.8-A's FEAT_NMI.

I've tested this series under a QEM KVM VM on a ThunderX2 host, and a
QEMU TCG VM on an x86_64 host. I've tested with and without pseudo-NMI
support enabled, and with pseudo-NMI debug and lockdep enabled, using
perf record in system-wide mode.

Thanks,
Mark.

Mark Rutland (4):
  arm64: rename ARM64_HAS_SYSREG_GIC_CPUIF to ARM64_HAS_GIC_SYSREG_CPUIF
  arm64: rename ARM64_HAS_IRQ_PRIO_MASKING to ARM64_HAS_GIC_PRIO_MASKING
  arm64: add ARM64_HAS_GIC_PRIO_NO_PMHE cpucap
  arm64: irqflags: use alternative branches for pseudo-NMI logic

 arch/arm/include/asm/arch_gicv3.h   |   5 +
 arch/arm64/include/asm/arch_gicv3.h |   5 +
 arch/arm64/include/asm/barrier.h    |  11 +-
 arch/arm64/include/asm/cpufeature.h |   2 +-
 arch/arm64/include/asm/irqflags.h   | 183 +++++++++++++++++++---------
 arch/arm64/include/asm/ptrace.h     |   2 +-
 arch/arm64/kernel/cpufeature.c      |  26 +++-
 arch/arm64/kernel/entry.S           |  25 ++--
 arch/arm64/kernel/image-vars.h      |   2 -
 arch/arm64/tools/cpucaps            |   5 +-
 drivers/irqchip/irq-gic-v3.c        |  19 +--
 drivers/irqchip/irq-gic.c           |   2 +-
 12 files changed, 188 insertions(+), 99 deletions(-)