powerpc: Remove MSR_PR check in interrupt_exit_{user/kernel}_prepare()

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.leroy@csgroup.eu>
Acked-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/385ead49ccb66a259b25fee3eebf0bd4094068f3.1629707037.git.christophe.leroy@csgroup.eu

diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
index abc2b3d..531f0a1 100644 (file)
--- a/arch/powerpc/kernel/interrupt.c
+++ b/arch/powerpc/kernel/interrupt.c
@@ -464,7 +464,6 @@ 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);
 
@@ -498,7 +497,6 @@ 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.