irqchip/gic-v3: Fix priority mask handling

When a kernel is built with CONFIG_ARM64_PSEUDO_NMI=y and pseudo-NMIs
are enabled at runtime, GICv3's gic_handle_irq() can leave DAIF and
ICC_PMR_EL1 in an unexpected state in some cases, breaking subsequent
usage of local_irq_enable() and resulting in softirqs being run with
IRQs erroneously masked (possibly resulting in deadlocks).

This can happen when an IRQ exception is taken from a context where
regular IRQs were unmasked, and either:

(1) ICC_IAR1_EL1 indicates a special INTID (e.g. as a result of an IRQ
    being withdrawn since the IRQ exception was taken).

(2) ICC_IAR1_EL1 and ICC_RPR_EL1 indicate an NMI was acknowledged.

When an NMI is taken from a context where regular IRQs were masked,
there is no problem.

When CONFIG_ARM64_DEBUG_PRIORITY_MASKING=y, this can be detected with
perf, e.g.

| # ./perf record -a -g -e cycles:k ls -alR / > /dev/null 2>&1
| ------------[ cut here ]------------
| WARNING: CPU: 0 PID: 14 at arch/arm64/include/asm/irqflags.h:32 arch_local_irq_enable+0x4c/0x6c
| Modules linked in:
| CPU: 0 PID: 14 Comm: ksoftirqd/0 Not tainted 5.18.0-rc5-00004-g876c38e3d20b #12
| Hardware name: linux,dummy-virt (DT)
| pstate: 204000c5 (nzCv daIF +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
| pc : arch_local_irq_enable+0x4c/0x6c
| lr : __do_softirq+0x110/0x5d8
| sp : ffff8000080bbbc0
| pmr_save: 000000f0
| x29: ffff8000080bbbc0 x28: ffff316ac3a6ca40 x27: 0000000000000000
| x26: 0000000000000000 x25: ffffa04611c06008 x24: ffffa04611c06008
| x23: 0000000040400005 x22: 0000000000000200 x21: ffff8000080bbe20
| x20: ffffa0460fe10320 x19: 0000000000000009 x18: 0000000000000000
| x17: ffff91252dfa9000 x16: ffff800008004000 x15: 0000000000004000
| x14: 0000000000000028 x13: ffffa0460fe17578 x12: ffffa0460fed4294
| x11: ffffa0460fedc168 x10: ffffffffffffff80 x9 : ffffa0460fe10a70
| x8 : ffffa0460fedc168 x7 : 000000000000b762 x6 : 00000000057c3bdf
| x5 : ffff8000080bbb18 x4 : 0000000000000000 x3 : 0000000000000001
| x2 : ffff91252dfa9000 x1 : 0000000000000060 x0 : 00000000000000f0
| Call trace:
|  arch_local_irq_enable+0x4c/0x6c
|  __irq_exit_rcu+0x180/0x1ac
|  irq_exit_rcu+0x1c/0x44
|  el1_interrupt+0x4c/0xe4
|  el1h_64_irq_handler+0x18/0x24
|  el1h_64_irq+0x74/0x78
|  smpboot_thread_fn+0x68/0x2c0
|  kthread+0x124/0x130
|  ret_from_fork+0x10/0x20
| irq event stamp: 193241
| hardirqs last  enabled at (193240): [<ffffa0460fe10a9c>] __do_softirq+0x10c/0x5d8
| hardirqs last disabled at (193241): [<ffffa0461102ffe4>] el1_dbg+0x24/0x90
| softirqs last  enabled at (193234): [<ffffa0460fe10e00>] __do_softirq+0x470/0x5d8
| softirqs last disabled at (193239): [<ffffa0460fea9944>] __irq_exit_rcu+0x180/0x1ac
| ---[ end trace 0000000000000000 ]---

The necessary manipulation of DAIF and ICC_PMR_EL1 depends on the
interrupted context, but the structure of gic_handle_irq() makes this
also depend on whether the GIC reports an IRQ, NMI, or special INTID:

*  When the interrupted context had regular IRQs masked (and hence the
   interrupt must be an NMI), the entry code performs the NMI
   entry/exit and gic_handle_irq() should return with DAIF and
   ICC_PMR_EL1 unchanged.

   This is handled correctly today.

* When the interrupted context had regular IRQs unmasked, the entry code
  performs IRQ entry/exit, but expects gic_handle_irq() to always update
  ICC_PMR_EL1 and DAIF.IF to unmask NMIs (but not regular IRQs) prior to
  returning (which it must do prior to invoking any regular IRQ
  handler).

  This unbalanced calling convention is necessary because we don't know
  whether an NMI has been taken until acknowledged by a read from
  ICC_IAR1_EL1, and so we need to perform the read with NMI masked in
  case an NMI has been taken (and needs to be handled with NMIs masked).

  Unfortunately, this is not handled consistently:

  - When ICC_IAR1_EL1 reports a special INTID, gic_handle_irq() returns
    immediately without manipulating ICC_PMR_EL1 and DAIF.

  - When RPR_EL1 indicates an NMI, gic_handle_irq() calls
    gic_handle_nmi() to invoke the NMI handler, then returns without
    manipulating ICC_PMR_EL1 and DAIF.

  - For regular IRQs, gic_handle_irq() manipulates ICC_PMR_EL1 and DAIF
    prior to invoking the IRQ handler.

There were related problems with special INTID handling in the past,
where if an exception was taken from a context with regular IRQs masked
and ICC_IAR_EL1 reported a special INTID, gic_handle_irq() would
erroneously unmask NMIs in NMI context permitted an unexpected nested
NMI. That case specifically was fixed by commit:

  a97709f563a078e2 ("irqchip/gic-v3: Do not enable irqs when handling spurious interrups")

... but unfortunately that commit added an inverse problem, where if an
exception was taken from a context with regular IRQs *unmasked* and
ICC_IAR_EL1 reported a special INTID, gic_handle_irq() would erroneously
fail to  unmask NMIs (and consequently regular IRQs could not be
unmasked during softirq processing). Before and after that commit, if an
NMI was taken from a context with regular IRQs unmasked gic_handle_irq()
would not unmask NMIs prior to returning, leading to the same problem
with softirq handling.

This patch fixes this by restructuring gic_handle_irq(), splitting it
into separate irqson/irqsoff helper functions which consistently perform
the DAIF + ICC_PMR1_EL1 manipulation based upon the interrupted context,
regardless of the event indicated by ICC_IAR1_EL1.

The special INTID handling is moved into the low-level IRQ/NMI handler
invocation helper functions, so that early returns don't prevent the
required manipulation of DAIF + ICC_PMR_EL1.

Fixes: f32c926651dcd168 ("irqchip/gic-v3: Handle pseudo-NMIs")
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220513133038.226182-4-mark.rutland@arm.com

0 files changed, 0 insertions, 0 deletions