Re: [PATCH v9 12/26] arm64: irqflags: Use ICC_PMR_EL1 for interrupt masking

[Ard Biesheuvel]

On Mon, 21 Jan 2019 at 16:34, Julien Thierry <julien.thierry@xxxxxxx> 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@xxxxxxx>
> Suggested-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Will Deacon <will.deacon@xxxxxxx>
> Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
> ---
>  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@xxxxxxxxxx>

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
>