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   1 From 65722736c3baf29e02e964a09e85c9ef71c48e8d Mon Sep 17 00:00:00 2001
   2 From: Nicholas Piggin <npiggin@gmail.com>
   3 Date: Sat, 22 Oct 2022 15:22:07 +1000
   4 Subject: powerpc/64s/interrupt: Fix clear of PACA_IRQS_HARD_DIS when returning to soft-masked context
   5
   6 From: Nicholas Piggin <npiggin@gmail.com>
   7
   8 commit 65722736c3baf29e02e964a09e85c9ef71c48e8d upstream.
   9
  10 Commit a4cb3651a1743 ("powerpc/64s/interrupt: Fix lost interrupts when
  11 returning to soft-masked context") fixed the problem of pending irqs
  12 being cleared when clearing the HARD_DIS bit, but then it didn't clear
  13 the bit at all. This change clears HARD_DIS without affecting other bits
  14 in the mask.
  15
  16 When an interrupt hits in a soft-masked section that has MSR[EE]=1, it
  17 can hard disable and set PACA_IRQS_HARD_DIS, which must be cleared when
  18 returning to the EE=1 caller (unless it was set due to a MUST_HARD_MASK
  19 interrupt becoming pending). Failure to clear this leaves the
  20 returned-to context running with MSR[EE]=1 and PACA_IRQS_HARD_DIS, which
  21 confuses irq assertions and could be dangerous for code that might test
  22 the flag.
  23
  24 This was observed in a hash MMU kernel where a kernel hash fault hits in
  25 a local_irqs_disabled region that has EE=1. The hash fault also runs
  26 with EE=1, then as it returns, a decrementer hits in the restart section
  27 and the irq restart code hard-masks which sets the PACA_IRQ_HARD_DIS
  28 flag, which is not clear when the original context is returned to.
  29
  30 Reported-by: Sachin Sant <sachinp@linux.ibm.com>
  31 Fixes: a4cb3651a1743 ("powerpc/64s/interrupt: Fix lost interrupts when returning to soft-masked context")
  32 Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
  33 Tested-by: Sachin Sant <sachinp@linux.ibm.com>
  34 Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
  35 Link: https://lore.kernel.org/r/20221022052207.471328-1-npiggin@gmail.com
  36 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  37 ---
  38  arch/powerpc/kernel/interrupt_64.S |   13 +++++++++++--
  39  1 file changed, 11 insertions(+), 2 deletions(-)
  40
  41 --- a/arch/powerpc/kernel/interrupt_64.S
  42 +++ b/arch/powerpc/kernel/interrupt_64.S
  43 @@ -565,15 +565,24 @@ _ASM_NOKPROBE_SYMBOL(interrupt_return_\s
  44          * Returning to soft-disabled context.
  45          * Check if a MUST_HARD_MASK interrupt has become pending, in which
  46          * case we need to disable MSR[EE] in the return context.
  47 +        *
  48 +        * The MSR[EE] check catches among other things the short incoherency
  49 +        * in hard_irq_disable() between clearing MSR[EE] and setting
  50 +        * PACA_IRQ_HARD_DIS.
  51          */
  52         ld      r12,_MSR(r1)
  53         andi.   r10,r12,MSR_EE
  54         beq     .Lfast_kernel_interrupt_return_\srr\() // EE already disabled
  55         lbz     r11,PACAIRQHAPPENED(r13)
  56         andi.   r10,r11,PACA_IRQ_MUST_HARD_MASK
  57 -       beq     .Lfast_kernel_interrupt_return_\srr\() // No HARD_MASK pending
  58 +       bne     1f // HARD_MASK is pending
  59 +       // No HARD_MASK pending, clear possible HARD_DIS set by interrupt
  60 +       andi.   r11,r11,(~PACA_IRQ_HARD_DIS)@l
  61 +       stb     r11,PACAIRQHAPPENED(r13)
  62 +       b       .Lfast_kernel_interrupt_return_\srr\()
  63
  64 -       /* Must clear MSR_EE from _MSR */
  65 +
  66 +1:     /* Must clear MSR_EE from _MSR */
  67  #ifdef CONFIG_PPC_BOOK3S
  68         li      r10,0
  69         /* Clear valid before changing _MSR */