Re: [PATCH v6 07/24] arm64: Make PMR part of task context

[Mark Rutland]

On Mon, Nov 12, 2018 at 11:56:58AM +0000, Julien Thierry wrote:
> If ICC_PMR_EL1 is used to mask interrupts, its value should be
> saved/restored whenever a task is context switched out/in or
> gets an exception.
> 
> Add PMR to the registers to save in the pt_regs struct upon kernel entry,
> and restore it before ERET. Also, initialize it to a sane value when
> creating new tasks.

Could you please elaborate on when this matters?

Does this actually matter for context-switch? Can we do that in a
pseudo-NMI handler?

Or does this only matter for exception entry/return, and not
context-switch?

Thanks,
Mark.

> Signed-off-by: Julien Thierry <julien.thierry@xxxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Will Deacon <will.deacon@xxxxxxx>
> Cc: Dave Martin <Dave.Martin@xxxxxxx>
> ---
>  arch/arm64/include/asm/processor.h |  3 +++
>  arch/arm64/include/asm/ptrace.h    | 14 +++++++++++---
>  arch/arm64/kernel/asm-offsets.c    |  1 +
>  arch/arm64/kernel/entry.S          | 13 +++++++++++++
>  arch/arm64/kernel/process.c        |  6 ++++++
>  5 files changed, 34 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
> index 6b0d4df..b2315ef 100644
> --- a/arch/arm64/include/asm/processor.h
> +++ b/arch/arm64/include/asm/processor.h
> @@ -168,6 +168,9 @@ static inline void start_thread_common(struct pt_regs *regs, unsigned long pc)
>  	memset(regs, 0, sizeof(*regs));
>  	forget_syscall(regs);
>  	regs->pc = pc;
> +
> +	if (system_supports_irq_prio_masking())
> +		regs->pmr_save = GIC_PRIO_IRQON;
>  }
>  
>  static inline void start_thread(struct pt_regs *regs, unsigned long pc,
> diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h
> index ce6998c..0ad46f5 100644
> --- a/arch/arm64/include/asm/ptrace.h
> +++ b/arch/arm64/include/asm/ptrace.h
> @@ -19,6 +19,8 @@
>  #ifndef __ASM_PTRACE_H
>  #define __ASM_PTRACE_H
>  
> +#include <asm/cpufeature.h>
> +
>  #include <uapi/asm/ptrace.h>
>  
>  /* Current Exception Level values, as contained in CurrentEL */
> @@ -173,7 +175,8 @@ struct pt_regs {
>  #endif
>  
>  	u64 orig_addr_limit;
> -	u64 unused;	// maintain 16 byte alignment
> +	/* Only valid when ARM64_HAS_IRQ_PRIO_MASKING is enabled. */
> +	u64 pmr_save;
>  	u64 stackframe[2];
>  };
>  
> @@ -208,8 +211,13 @@ static inline void forget_syscall(struct pt_regs *regs)
>  #define processor_mode(regs) \
>  	((regs)->pstate & PSR_MODE_MASK)
>  
> -#define interrupts_enabled(regs) \
> -	(!((regs)->pstate & PSR_I_BIT))
> +#define irqs_priority_unmasked(regs)					\
> +	(system_supports_irq_prio_masking() ?				\
> +		(regs)->pmr_save & GIC_PRIO_STATUS_BIT :		\
> +		true)
> +
> +#define interrupts_enabled(regs)			\
> +	(!((regs)->pstate & PSR_I_BIT) && irqs_priority_unmasked(regs))
>  
>  #define fast_interrupts_enabled(regs) \
>  	(!((regs)->pstate & PSR_F_BIT))
> diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
> index 323aeb5..bab4122 100644
> --- a/arch/arm64/kernel/asm-offsets.c
> +++ b/arch/arm64/kernel/asm-offsets.c
> @@ -78,6 +78,7 @@ int main(void)
>    DEFINE(S_ORIG_X0,		offsetof(struct pt_regs, orig_x0));
>    DEFINE(S_SYSCALLNO,		offsetof(struct pt_regs, syscallno));
>    DEFINE(S_ORIG_ADDR_LIMIT,	offsetof(struct pt_regs, orig_addr_limit));
> +  DEFINE(S_PMR_SAVE,		offsetof(struct pt_regs, pmr_save));
>    DEFINE(S_STACKFRAME,		offsetof(struct pt_regs, stackframe));
>    DEFINE(S_FRAME_SIZE,		sizeof(struct pt_regs));
>    BLANK();
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index 039144e..eb8120e 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -249,6 +249,12 @@ alternative_else_nop_endif
>  	msr	sp_el0, tsk
>  	.endif
>  
> +	/* Save pmr */
> +alternative_if ARM64_HAS_IRQ_PRIO_MASKING
> +	mrs_s	x20, SYS_ICC_PMR_EL1
> +	str	x20, [sp, #S_PMR_SAVE]
> +alternative_else_nop_endif
> +
>  	/*
>  	 * Registers that may be useful after this macro is invoked:
>  	 *
> @@ -269,6 +275,13 @@ alternative_else_nop_endif
>  	/* No need to restore UAO, it will be restored from SPSR_EL1 */
>  	.endif
>  
> +	/* Restore pmr */
> +alternative_if ARM64_HAS_IRQ_PRIO_MASKING
> +	ldr	x20, [sp, #S_PMR_SAVE]
> +	msr_s	SYS_ICC_PMR_EL1, x20
> +	dsb	sy
> +alternative_else_nop_endif
> +
>  	ldp	x21, x22, [sp, #S_PC]		// load ELR, SPSR
>  	.if	\el == 0
>  	ct_user_enter
> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> index d9a4c2d..71e8850 100644
> --- a/arch/arm64/kernel/process.c
> +++ b/arch/arm64/kernel/process.c
> @@ -231,6 +231,9 @@ void __show_regs(struct pt_regs *regs)
>  
>  	printk("sp : %016llx\n", sp);
>  
> +	if (system_supports_irq_prio_masking())
> +		printk("pmr_save: %08llx\n", regs->pmr_save);
> +
>  	i = top_reg;
>  
>  	while (i >= 0) {
> @@ -362,6 +365,9 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start,
>  		if (arm64_get_ssbd_state() == ARM64_SSBD_FORCE_DISABLE)
>  			childregs->pstate |= PSR_SSBS_BIT;
>  
> +		if (system_supports_irq_prio_masking())
> +			childregs->pmr_save = GIC_PRIO_IRQON;
> +
>  		p->thread.cpu_context.x19 = stack_start;
>  		p->thread.cpu_context.x20 = stk_sz;
>  	}
> -- 
> 1.9.1
>