[PATCH v3 0/2] irqchip/gic-v3: Support pseudo-NMIs when SCR_EL3.FIQ == 0

[Alexandru Elisei]

Trusted Firmware-A's default interrupt routing model is to clear
SCR_EL3.FIQ, which is the only case that GICv3 doesn't support. This series
tries to fix that by detecting it at runtime and using a different priority
value for ICC_PMR_EL1 when masking regular interrupts. As a result, we will
be able to support pseudo-NMIs on all combinations of GIC security states
and firmware configurations.

The first patch was there because when I started working on the PMU NMI
patches I found it confusing that there was no clear message stating that
NMIs were successfully enabled. The second patch is the main patch of the
series, where pseudo-NMIs are enabled even if SCR_EL3.FIQ == 0.

As an aside, the set of priorities that I've added would work in all cases
if there was no need to use GIC_PRIO_PSR_I_SET, but that is a much more
intrusive change and I'm not comfortable attempting it. I'm pretty sure I
will end up breaking things really badly.

I've tested the series using PMU NMIs [1], rebased on top of v5.9-rc4, on
the model and on espressobin-v7. Tests that I've run:

1. On the model:
- Host with SCR_EL3.FIQ == 1 (so using the original priorities), ran
  perf record -a -- iperf3 -c 127.0.0.1 -t 30.
- On a KVM guest (security disabled, so using the original priorities),
  ran the same command.

2. On an espressobin-v7:
- Host with SCR_EL3.FIQ == 0 (using the priority added by the series),
  ran perf record -a -- iperf3 -c 127.0.0.1 -t 60.
- On a KVM guest (security disabled, so using the original priorities),
  ran the same command.
- Stress test for one hour with CONFIG_ARM64_DEBUG_PRIORITY_MASKING set
  for the host and guest. On the host, I ran in parallel
  perf record -a -- iperf3 -c 127.0.0.1 -t 3600  and
  perf record -ae L1-dcache-loads -a -- sleep 3600. On the guest, I ran
  the same iperf3 command as on the host.

Changes since v2:
* Renamed gic_prio_irqoff() -> GIC_PRIO_IRQOFF, thus avoiding any changes
  to daifflags.h and irqflags.h, as per Marc's excellent suggestion.
* Added comment gic_cpu_sys_reg_init() explaining why we cannot get the
  warning on the boot CPU.

Changes since v1:
* Rebased on top of v5.9-rc1
* Changed pmr to u64 in arch_local_irq_{enable,disable} to stop
  clang from complaining and to match local_daif_restore().

[1] https://lkml.org/lkml/2020/8/19/671

Alexandru Elisei (2):
  irqchip/gicv3: Spell out when pseudo-NMIs are enabled
  irqchip/gic-v3: Support pseudo-NMIs when SCR_EL3.FIQ == 0

 arch/arm64/include/asm/arch_gicv3.h |  8 +++-
 arch/arm64/include/asm/ptrace.h     | 14 ++++++-
 arch/arm64/kernel/image-vars.h      |  2 +
 drivers/irqchip/irq-gic-v3.c        | 60 ++++++++++++++++++++++-------
 4 files changed, 68 insertions(+), 16 deletions(-)

-- 
2.28.0