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Date: Thu, 29 Nov 2018 16:46:00 +0000
From: Mark Rutland <mark.rutland@....com>
To: Julien Thierry <julien.thierry@....com>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
daniel.thompson@...aro.org, joel@...lfernandes.org,
marc.zyngier@....com, christoffer.dall@....com,
james.morse@....com, catalin.marinas@....com, will.deacon@....com,
Dave Martin <Dave.Martin@....com>
Subject: Re: [PATCH v6 07/24] arm64: Make PMR part of task context
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@....com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will.deacon@....com>
> Cc: Dave Martin <Dave.Martin@....com>
> ---
> 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
>
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