Re: [PATCH v3 1/3] powerpc: Remove MSR_PR check in interrupt_exit_{user/kernel}_prepare()

[Christophe Leroy]

Le 25/08/2021 à 07:27, Michael Ellerman a écrit :
> Christophe Leroy <christophe.leroy@xxxxxxxxxx> writes:
> > 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@xxxxxxxxxx>
> > Acked-by: Nicholas Piggin <npiggin@xxxxxxxxx>
> > ---
> >   arch/powerpc/kernel/interrupt.c | 2 --
> >   1 file changed, 2 deletions(-)
>
> I'll pick this one up independent of the other two patches.

Second patch should be ok as well, no ?

Christophe