On 22-Oct-2022, at 10:52 AM, Nicholas Piggin [off-list ref] wrote:

Commit a4cb3651a1743 ("powerpc/64s/interrupt: Fix lost interrupts when
returning to soft-masked context") fixed the problem of pending irqs
pending cleared when clearing the HARD_DIS bit, but then it didn't clear
the bit at all. This change clears HARD_DIS without affecting other bits
in the mask.

When an interrupt hits in a soft-masked section that has MSR[EE]=1, it
can hard disable and set PACA_IRQS_HARD_DIS,which  must be cleared
when returning to the EE=1 caller (unless it was set due to a
MUST_HARD_MASK interrupt becoming pending). Failure to clear this leaves
the returned-to context running with MSR[EE]=1 and PACA_IRQS_HARD_DIS,
which confuses irq assertions and could be dangerous for code that might
test the flag.

This was observed in a hash MMU kernel where a kernel hash fault hits in
a local_irqs_disabled region that has EE=1. The hash fault also runs
with EE=1, then as it returns, a decrementer hits in the restart section
and the irq restart code hard-masks which sets the PACA_IRQ_HARD_DIS
flag, which is not clear when the original context is returned to.

Reported-by: Sachin Sant <redacted>
Fixes: a4cb3651a1743 ("powerpc/64s/interrupt: Fix lost interrupts when returning to soft-masked context")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
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Thanks Nick. The patch fixes the reported problem

Tested-by: Sachin Sant <redacted>