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Date: Mon, 21 Jan 2019 16:45:15 +0100
From: Ard Biesheuvel <ard.biesheuvel@...aro.org>
To: Julien Thierry <julien.thierry@....com>
Cc: linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Daniel Thompson <daniel.thompson@...aro.org>,
Joel Fernandes <joel@...lfernandes.org>,
Marc Zyngier <marc.zyngier@....com>,
Christoffer Dall <christoffer.dall@....com>,
James Morse <james.morse@....com>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will.deacon@....com>,
Mark Rutland <mark.rutland@....com>,
Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH v9 12/26] arm64: irqflags: Use ICC_PMR_EL1 for interrupt masking
On Mon, 21 Jan 2019 at 16:34, Julien Thierry <julien.thierry@....com> wrote:
>
> Instead disabling interrupts by setting the PSR.I bit, use a priority
> higher than the one used for interrupts to mask them via PMR.
>
> When using PMR to disable interrupts, the value of PMR will be used
> instead of PSR.[DAIF] for the irqflags.
>
> Signed-off-by: Julien Thierry <julien.thierry@....com>
> Suggested-by: Daniel Thompson <daniel.thompson@...aro.org>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will.deacon@....com>
> Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> Cc: Oleg Nesterov <oleg@...hat.com>
> ---
> arch/arm64/include/asm/efi.h | 6 +++
> arch/arm64/include/asm/irqflags.h | 104 ++++++++++++++++++++++++++++----------
> 2 files changed, 82 insertions(+), 28 deletions(-)
>
> diff --git a/arch/arm64/include/asm/efi.h b/arch/arm64/include/asm/efi.h
> index 7ed3208..3db6772 100644
> --- a/arch/arm64/include/asm/efi.h
> +++ b/arch/arm64/include/asm/efi.h
> @@ -44,6 +44,12 @@
>
> #define ARCH_EFI_IRQ_FLAGS_MASK (PSR_D_BIT | PSR_A_BIT | PSR_I_BIT | PSR_F_BIT)
>
> +#define arch_efi_save_flags(state_flags) \
> + ((void)((state_flags) = read_sysreg(daif)))
> +
> +#define arch_efi_restore_flags(state_flags) write_sysreg(state_flags, daif)
> +
> +
> /* arch specific definitions used by the stub code */
>
> /*
For the EFI changes
Acked-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
although it deserves a comment as to why it is unaffected by
ARM64_HAS_IRQ_PRIO_MASKING
> diff --git a/arch/arm64/include/asm/irqflags.h b/arch/arm64/include/asm/irqflags.h
> index 24692ed..7e82a92 100644
> --- a/arch/arm64/include/asm/irqflags.h
> +++ b/arch/arm64/include/asm/irqflags.h
> @@ -18,7 +18,9 @@
>
> #ifdef __KERNEL__
>
> +#include <asm/alternative.h>
> #include <asm/ptrace.h>
> +#include <asm/sysreg.h>
>
> /*
> * Aarch64 has flags for masking: Debug, Asynchronous (serror), Interrupts and
> @@ -36,33 +38,31 @@
> /*
> * CPU interrupt mask handling.
> */
> -static inline unsigned long arch_local_irq_save(void)
> -{
> - unsigned long flags;
> - asm volatile(
> - "mrs %0, daif // arch_local_irq_save\n"
> - "msr daifset, #2"
> - : "=r" (flags)
> - :
> - : "memory");
> - return flags;
> -}
> -
> static inline void arch_local_irq_enable(void)
> {
> - asm volatile(
> - "msr daifclr, #2 // arch_local_irq_enable"
> - :
> + unsigned long unmasked = GIC_PRIO_IRQON;
> +
> + asm volatile(ALTERNATIVE(
> + "msr daifclr, #2 // arch_local_irq_enable\n"
> + "nop",
> + "msr_s " __stringify(SYS_ICC_PMR_EL1) ",%0\n"
> + "dsb sy",
> + ARM64_HAS_IRQ_PRIO_MASKING)
> :
> + : "r" (unmasked)
> : "memory");
> }
>
> static inline void arch_local_irq_disable(void)
> {
> - asm volatile(
> - "msr daifset, #2 // arch_local_irq_disable"
> - :
> + unsigned long masked = GIC_PRIO_IRQOFF;
> +
> + asm volatile(ALTERNATIVE(
> + "msr daifset, #2 // arch_local_irq_disable",
> + "msr_s " __stringify(SYS_ICC_PMR_EL1) ", %0",
> + ARM64_HAS_IRQ_PRIO_MASKING)
> :
> + : "r" (masked)
> : "memory");
> }
>
> @@ -71,12 +71,44 @@ static inline void arch_local_irq_disable(void)
> */
> static inline unsigned long arch_local_save_flags(void)
> {
> + unsigned long daif_bits;
> unsigned long flags;
> - asm volatile(
> - "mrs %0, daif // arch_local_save_flags"
> - : "=r" (flags)
> - :
> +
> + daif_bits = read_sysreg(daif);
> +
> + /*
> + * The asm is logically equivalent to:
> + *
> + * if (system_uses_irq_prio_masking())
> + * flags = (daif_bits & PSR_I_BIT) ?
> + * GIC_PRIO_IRQOFF :
> + * read_sysreg_s(SYS_ICC_PMR_EL1);
> + * else
> + * flags = daif_bits;
> + */
> + asm volatile(ALTERNATIVE(
> + "mov %0, %1\n"
> + "nop\n"
> + "nop",
> + "mrs_s %0, " __stringify(SYS_ICC_PMR_EL1) "\n"
> + "ands %1, %1, " __stringify(PSR_I_BIT) "\n"
> + "csel %0, %0, %2, eq",
> + ARM64_HAS_IRQ_PRIO_MASKING)
> + : "=&r" (flags), "+r" (daif_bits)
> + : "r" (GIC_PRIO_IRQOFF)
> : "memory");
> +
> + return flags;
> +}
> +
> +static inline unsigned long arch_local_irq_save(void)
> +{
> + unsigned long flags;
> +
> + flags = arch_local_save_flags();
> +
> + arch_local_irq_disable();
> +
> return flags;
> }
>
> @@ -85,16 +117,32 @@ static inline unsigned long arch_local_save_flags(void)
> */
> static inline void arch_local_irq_restore(unsigned long flags)
> {
> - asm volatile(
> - "msr daif, %0 // arch_local_irq_restore"
> - :
> - : "r" (flags)
> - : "memory");
> + asm volatile(ALTERNATIVE(
> + "msr daif, %0\n"
> + "nop",
> + "msr_s " __stringify(SYS_ICC_PMR_EL1) ", %0\n"
> + "dsb sy",
> + ARM64_HAS_IRQ_PRIO_MASKING)
> + : "+r" (flags)
> + :
> + : "memory");
> }
>
> static inline int arch_irqs_disabled_flags(unsigned long flags)
> {
> - return flags & PSR_I_BIT;
> + int res;
> +
> + asm volatile(ALTERNATIVE(
> + "and %w0, %w1, #" __stringify(PSR_I_BIT) "\n"
> + "nop",
> + "cmp %w1, #" __stringify(GIC_PRIO_IRQOFF) "\n"
> + "cset %w0, ls",
> + ARM64_HAS_IRQ_PRIO_MASKING)
> + : "=&r" (res)
> + : "r" ((int) flags)
> + : "memory");
> +
> + return res;
> }
> #endif
> #endif
> --
> 1.9.1
>
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