[PATCH 1/3] powerpc: Remove MSR_PR check in interrupt_exit_{user/kernel}_prepare()

[Christophe Leroy]

In those hot functions that are called at every interrupt, any saved
cycle is worth it.

interrupt_exit_user_prepare() and interrupt_exit_kernel_prepare() are
called from three places:
- From entry_32.S
- From interrupt_64.S
- From interrupt_exit_user_restart() and interrupt_exit_kernel_restart()

In entry_32.S, there are inambiguously called based on MSR_PR:

        interrupt_return:
                lwz     r4,_MSR(r1)
                addi    r3,r1,STACK_FRAME_OVERHEAD
                andi.   r0,r4,MSR_PR
                beq     .Lkernel_interrupt_return
                bl      interrupt_exit_user_prepare
        ...
        .Lkernel_interrupt_return:
                bl      interrupt_exit_kernel_prepare

In interrupt_64.S, that's similar:

        interrupt_return_\srr\():
                ld      r4,_MSR(r1)
                andi.   r0,r4,MSR_PR
                beq     interrupt_return_\srr\()_kernel
        interrupt_return_\srr\()_user: /* make backtraces match the _kernel 
variant */
                addi    r3,r1,STACK_FRAME_OVERHEAD
                bl      interrupt_exit_user_prepare
        ...
        interrupt_return_\srr\()_kernel:
                addi    r3,r1,STACK_FRAME_OVERHEAD
                bl      interrupt_exit_kernel_prepare

In interrupt_exit_user_restart() and interrupt_exit_kernel_restart(),
MSR_PR is verified respectively by BUG_ON(!user_mode(regs)) and
BUG_ON(user_mode(regs)) prior to calling interrupt_exit_user_prepare()
and interrupt_exit_kernel_prepare().

The verification in interrupt_exit_user_prepare() and
interrupt_exit_kernel_prepare() are therefore useless and can be removed.

Signed-off-by: Christophe Leroy <christophe.le...@csgroup.eu>
Acked-by: Nicholas Piggin <npig...@gmail.com>
---
 arch/powerpc/kernel/interrupt.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
index 21bbd615ca41..f26caf911ab5 100644
--- a/arch/powerpc/kernel/interrupt.c
+++ b/arch/powerpc/kernel/interrupt.c
@@ -465,7 +465,6 @@ notrace unsigned long interrupt_exit_user_prepare(struct 
pt_regs *regs)
 
        if (!IS_ENABLED(CONFIG_BOOKE) && !IS_ENABLED(CONFIG_40x))
                BUG_ON(!(regs->msr & MSR_RI));
-       BUG_ON(!(regs->msr & MSR_PR));
        BUG_ON(arch_irq_disabled_regs(regs));
        CT_WARN_ON(ct_state() == CONTEXT_USER);
 
@@ -499,7 +498,6 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct 
pt_regs *regs)
        if (!IS_ENABLED(CONFIG_BOOKE) && !IS_ENABLED(CONFIG_40x) &&
            unlikely(!(regs->msr & MSR_RI)))
                unrecoverable_exception(regs);
-       BUG_ON(regs->msr & MSR_PR);
        /*
         * CT_WARN_ON comes here via program_check_exception,
         * so avoid recursion.
-- 
2.25.0