powerpc/64s/interrupt: Fix lost interrupts when returning to soft-masked context

commit a4cb3651a174366cc85a677da9e3681fbe97fdae upstream.

It's possible for an interrupt returning to an irqs-disabled context to
lose a pending soft-masked irq because it branches to part of the exit
code for irqs-enabled contexts, which is meant to clear only the
PACA_IRQS_HARD_DIS flag from PACAIRQHAPPENED by zeroing the byte. This
just looks like a simple thinko from a recent commit (if there was no
hard mask pending, there would be no reason to clear it anyway).

This also adds comment to the code that actually does need to clear the
flag.

Fixes: e485f6c751e0a ("powerpc/64/interrupt: Fix return to masked context after hard-mask irq becomes pending")
Reported-by: Sachin Sant <sachinp@linux.ibm.com>
Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221013064418.1311104-1-npiggin@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/powerpc/kernel/interrupt_64.S b/arch/powerpc/kernel/interrupt_64.S
index d76376ce7291eb83d5fbd0c3badd9d8b38c41a00..2ca1c037ea2584b13c6aaea69b9a2fe03f493f15 100644 (file)
--- a/arch/powerpc/kernel/interrupt_64.S
+++ b/arch/powerpc/kernel/interrupt_64.S
@@ -571,7 +571,7 @@ _ASM_NOKPROBE_SYMBOL(interrupt_return_\srr\()_kernel)
        beq     .Lfast_kernel_interrupt_return_\srr\() // EE already disabled
        lbz     r11,PACAIRQHAPPENED(r13)
        andi.   r10,r11,PACA_IRQ_MUST_HARD_MASK
-       beq     1f // No HARD_MASK pending
+       beq     .Lfast_kernel_interrupt_return_\srr\() // No HARD_MASK pending
 
        /* Must clear MSR_EE from _MSR */
 #ifdef CONFIG_PPC_BOOK3S
@@ -588,12 +588,23 @@ _ASM_NOKPROBE_SYMBOL(interrupt_return_\srr\()_kernel)
        b       .Lfast_kernel_interrupt_return_\srr\()
 
 .Linterrupt_return_\srr\()_soft_enabled:
+       /*
+        * In the soft-enabled case, need to double-check that we have no
+        * pending interrupts that might have come in before we reached the
+        * restart section of code, and restart the exit so those can be
+        * handled.
+        *
+        * If there are none, it is be possible that the interrupt still
+        * has PACA_IRQ_HARD_DIS set, which needs to be cleared for the
+        * interrupted context. This clear will not clobber a new pending
+        * interrupt coming in, because we're in the restart section, so
+        * such would return to the restart location.
+        */
 #ifdef CONFIG_PPC_BOOK3S
        lbz     r11,PACAIRQHAPPENED(r13)
        andi.   r11,r11,(~PACA_IRQ_HARD_DIS)@l
        bne-    interrupt_return_\srr\()_kernel_restart
 #endif
-1:
        li      r11,0
        stb     r11,PACAIRQHAPPENED(r13) // clear the possible HARD_DIS