[PATCH 14/14] powerpc/64s: use the same default PPR for user and kernel
Christophe Leroy
christophe.leroy at csgroup.eu
Tue May 18 00:09:05 AEST 2021
Le 15/03/2021 à 23:04, Nicholas Piggin a écrit :
> Change the default PPR to userspace to 4 (medium), matching the
> normal kernel PPR.
>
> This allows system calls and user interrupts to avoid setting PPR on
> entry and exit, providing a significant speedup.
>
> This is a change to the user environment. The problem with changing
> the kernel to match userspace at 3 (medium-low), is that userspace
> can then boost priority above the kernel which is also undesirable.
>
> glibc does not seem to change PPR anywhere, so the decision is to
> go with this.
>
> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
> ---
> arch/powerpc/include/asm/interrupt.h | 2 ++
> arch/powerpc/include/asm/processor.h | 4 ++--
> arch/powerpc/kernel/exceptions-64s.S | 3 ---
> arch/powerpc/kernel/interrupt.c | 33 ++++++++++++++++++++++++++++
> arch/powerpc/kernel/interrupt_64.S | 17 --------------
> 5 files changed, 37 insertions(+), 22 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/interrupt.h b/arch/powerpc/include/asm/interrupt.h
> index d6d54bbcba2f..293e6be9fd71 100644
> --- a/arch/powerpc/include/asm/interrupt.h
> +++ b/arch/powerpc/include/asm/interrupt.h
> @@ -57,6 +57,8 @@ static inline void interrupt_enter_prepare(struct pt_regs *regs, struct interrup
> #ifdef CONFIG_PPC64
> bool trace_enable = false;
>
> + if (unlikely(regs->ppr != DEFAULT_PPR))
> + mtspr(SPRN_PPR, DEFAULT_PPR);
> if (IS_ENABLED(CONFIG_TRACE_IRQFLAGS)) {
> if (irq_soft_mask_set_return(IRQS_DISABLED) == IRQS_ENABLED)
> trace_enable = true;
> diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h
> index cb1edf21a82e..5ff589042103 100644
> --- a/arch/powerpc/include/asm/processor.h
> +++ b/arch/powerpc/include/asm/processor.h
> @@ -27,8 +27,8 @@
> #endif
>
> #ifdef CONFIG_PPC64
> -/* Default SMT priority is set to 3. Use 11- 13bits to save priority. */
> -#define PPR_PRIORITY 3
> +/* Default SMT priority is set to 4. Use 11- 13bits to save priority. */
> +#define PPR_PRIORITY 4
> #ifdef __ASSEMBLY__
> #define DEFAULT_PPR (PPR_PRIORITY << 50)
> #else
> diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
> index 75cee7cdf887..0d40614d13e0 100644
> --- a/arch/powerpc/kernel/exceptions-64s.S
> +++ b/arch/powerpc/kernel/exceptions-64s.S
> @@ -367,7 +367,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
> BEGIN_FTR_SECTION
> mfspr r9,SPRN_PPR
> END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
> - HMT_MEDIUM
> std r10,IAREA+EX_R10(r13) /* save r10 - r12 */
> BEGIN_FTR_SECTION
> mfspr r10,SPRN_CFAR
> @@ -1962,8 +1961,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_REAL_LE)
> mfspr r11,SPRN_SRR0
> mfspr r12,SPRN_SRR1
>
> - HMT_MEDIUM
> -
> .if ! \virt
> __LOAD_HANDLER(r10, system_call_common_real)
> mtctr r10
> diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
> index 09cf699d0e2e..a6e0595da0dd 100644
> --- a/arch/powerpc/kernel/interrupt.c
> +++ b/arch/powerpc/kernel/interrupt.c
> @@ -40,6 +40,11 @@ notrace long system_call_exception(long r3, long r4, long r5,
>
> regs->orig_gpr3 = r3;
>
> +#ifdef CONFIG_PPC_BOOK3S_64
> + if (unlikely(regs->ppr != DEFAULT_PPR))
> + mtspr(SPRN_PPR, DEFAULT_PPR);
> +#endif
Can you have some helper functions to do this instead of those 4 lines #ifdefed blocks all over the
place ?
Something like
#ifdef CONFIG_PPC_BOOK3S_64
static inline void set_ppr_regs(struct pt_regs *regs)
{
if (unlikely(regs->ppr != DEFAULT_PPR))
mtspr(SPRN_PPR, regs->ppr);
}
static inline void set_ppr_default(struct pt_regs *regs)
{
if (unlikely(regs->ppr != DEFAULT_PPR))
mtspr(SPRN_PPR, DEFAULT_PPR);
}
#else
static inline void set_ppr_regs(struct pt_regs *regs) { }
static inline void set_ppr_default(struct pt_regs *regs) { }
#endif
> +
> if (IS_ENABLED(CONFIG_PPC_IRQ_SOFT_MASK_DEBUG))
> BUG_ON(irq_soft_mask_return() != IRQS_ALL_DISABLED);
>
> @@ -237,6 +242,11 @@ notrace unsigned long syscall_exit_prepare_main(unsigned long r3,
>
> account_cpu_user_exit();
>
> +#ifdef CONFIG_PPC_BOOK3S_64
> + if (unlikely(regs->ppr != DEFAULT_PPR))
> + mtspr(SPRN_PPR, regs->ppr);
> +#endif
> +
> #ifndef CONFIG_PPC_BOOK3E_64 /* BOOK3E not using this */
> /*
> * We do this at the end so that we do context switch with KERNEL AMR
> @@ -315,6 +325,11 @@ notrace unsigned long syscall_exit_restart(unsigned long r3, struct pt_regs *reg
> */
> hard_irq_disable();
>
> +#ifdef CONFIG_PPC_BOOK3S_64
> + if (unlikely(regs->ppr != DEFAULT_PPR))
> + mtspr(SPRN_PPR, DEFAULT_PPR);
> +#endif
> +
> trace_hardirqs_off();
> user_exit_irqoff();
> account_cpu_user_entry();
> @@ -398,6 +413,11 @@ notrace unsigned long interrupt_exit_user_prepare(struct pt_regs *regs)
>
> account_cpu_user_exit();
>
> +#ifdef CONFIG_PPC_BOOK3S_64
> + if (unlikely(regs->ppr != DEFAULT_PPR))
> + mtspr(SPRN_PPR, regs->ppr);
> +#endif
> +
> /*
> * We do this at the end so that we do context switch with KERNEL AMR
> */
> @@ -489,6 +509,11 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs)
> local_paca->tm_scratch = regs->msr;
> #endif
>
> +#ifdef CONFIG_PPC_BOOK3S_64
> + if (unlikely(regs->ppr != DEFAULT_PPR))
> + mtspr(SPRN_PPR, regs->ppr);
> +#endif
> +
> /*
> * Don't want to mfspr(SPRN_AMR) here, because this comes after mtmsr,
> * which would cause Read-After-Write stalls. Hence, we take the AMR
> @@ -505,6 +530,10 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs)
> notrace unsigned long interrupt_exit_user_restart(struct pt_regs *regs)
> {
> hard_irq_disable();
> +#ifdef CONFIG_PPC_BOOK3S_64
> + if (unlikely(regs->ppr != DEFAULT_PPR))
> + mtspr(SPRN_PPR, DEFAULT_PPR);
> +#endif
>
> trace_hardirqs_off();
> user_exit_irqoff();
> @@ -523,6 +552,10 @@ notrace unsigned long interrupt_exit_user_restart(struct pt_regs *regs)
> notrace unsigned long interrupt_exit_kernel_restart(struct pt_regs *regs)
> {
> hard_irq_disable();
> +#ifdef CONFIG_PPC_BOOK3S_64
> + if (unlikely(regs->ppr != DEFAULT_PPR))
> + mtspr(SPRN_PPR, DEFAULT_PPR);
> +#endif
>
> #ifndef CONFIG_PPC_BOOK3E_64
> set_kuap(AMR_KUAP_BLOCKED);
> diff --git a/arch/powerpc/kernel/interrupt_64.S b/arch/powerpc/kernel/interrupt_64.S
> index eef61800f734..53fc446dcbeb 100644
> --- a/arch/powerpc/kernel/interrupt_64.S
> +++ b/arch/powerpc/kernel/interrupt_64.S
> @@ -99,10 +99,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_TM)
> ld r11,exception_marker at toc(r2)
> std r11,-16(r10) /* "regshere" marker */
>
> -BEGIN_FTR_SECTION
> - HMT_MEDIUM
> -END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
> -
> ENTER_KERNEL_SECURITY_FALLBACK
>
> /*
> @@ -142,10 +138,6 @@ BEGIN_FTR_SECTION
> stdcx. r0,0,r1 /* to clear the reservation */
> END_FTR_SECTION_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS)
>
> -BEGIN_FTR_SECTION
> - HMT_MEDIUM_LOW
> -END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
> -
> cmpdi r3,0
> bne .Lsyscall_vectored_\name\()_restore_regs
>
> @@ -377,10 +369,6 @@ END_FTR_SECTION_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS)
> mtspr SPRN_XER,r0
> .Lsyscall_restore_regs_cont:
>
> -BEGIN_FTR_SECTION
> - HMT_MEDIUM_LOW
> -END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
> -
> /*
> * We don't need to restore AMR on the way back to userspace for KUAP.
> * The value of AMR only matters while we're in the kernel.
> @@ -533,11 +521,6 @@ _ASM_NOKPROBE_SYMBOL(interrupt_return_\srr\())
> tdnei r4,IRQS_ENABLED
>
> #ifdef CONFIG_PPC_BOOK3S
> -BEGIN_FTR_SECTION
> - ld r10,_PPR(r1)
> - mtspr SPRN_PPR,r10
> -END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
> -
> .ifc \srr,srr
> lbz r4,PACASRR_VALID(r13)
> .else
>
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