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SubjectRe: [PATCH v8 12/26] arm64: irqflags: Use ICC_PMR_EL1 for interrupt masking
On Tue, Jan 08, 2019 at 02:07:30PM +0000, Julien Thierry 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@arm.com>
> Suggested-by: Daniel Thompson <daniel.thompson@linaro.org>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Cc: Oleg Nesterov <oleg@redhat.com>
> ---
> arch/arm64/include/asm/efi.h | 11 ++++
> arch/arm64/include/asm/irqflags.h | 123 +++++++++++++++++++++++++++++---------
> 2 files changed, 106 insertions(+), 28 deletions(-)
>
> diff --git a/arch/arm64/include/asm/efi.h b/arch/arm64/include/asm/efi.h
> index 7ed3208..134ff6e 100644
> --- a/arch/arm64/include/asm/efi.h
> +++ b/arch/arm64/include/asm/efi.h
> @@ -44,6 +44,17 @@
>
> #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) \
> + do { \
> + (state_flags) = read_sysreg(daif); \
> + } while (0)
> +
> +#define arch_efi_restore_flags(state_flags) \
> + do { \
> + write_sysreg(state_flags, daif); \
> + } while (0)
> +
> +

Randomly commenting a few minor nits as I glance down my mailbox...

There's no need to protect single statements with do { } while(0).

Just protect an expression statement that could be misparsed with ( ).

->

#define arch_efi_save_flags(state_flags) ((state_flags) = read_sysreg(daif))
#define arch_efi_restore_flags(state_flags) write_sysreg(state_flags, daif)
[...]

> diff --git a/arch/arm64/include/asm/irqflags.h b/arch/arm64/include/asm/irqflags.h
> index 24692ed..fa3b06f 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
> @@ -36,47 +38,96 @@

[...]

> /*
> + * Having two ways to control interrupt status is a bit complicated. Some
> + * locations like exception entries will have PSR.I bit set by the architecture
> + * while PMR is unmasked.
> + * We need the irqflags to represent that interrupts are disabled in such cases.
> + *
> + * For this, we lower the value read from PMR when the I bit is set so it is
> + * considered as an irq masking priority. (With PMR, lower value means masking
> + * more interrupts).
> + */
> +#define _get_irqflags(daif_bits, pmr) \
> +({ \
> + unsigned long flags; \
> + \
> + BUILD_BUG_ON(GIC_PRIO_IRQOFF < (GIC_PRIO_IRQON & ~PSR_I_BIT)); \
> + asm volatile(ALTERNATIVE( \
> + "mov %0, %1\n" \
> + "nop\n" \
> + "nop", \
> + "and %0, %1, #" __stringify(PSR_I_BIT) "\n" \
> + "mvn %0, %0\n" \
> + "and %0, %0, %2", \
> + ARM64_HAS_IRQ_PRIO_MASKING) \
> + : "=&r" (flags) \
> + : "r" (daif_bits), "r" (pmr) \
> + : "memory"); \
> + \
> + flags; \
> +})

Nit: does this need to be a macro?

({ ... }) is mildly gross and it's preferable to avoid it if the code
works just as well without...
pmr would need to be passed as a pointer, with "r" (*pmr) in the asm,
but I think it would compile down to precisely the same code.

> +
> +/*
> * Save the current interrupt enable state.
> */
> static inline unsigned long arch_local_save_flags(void)
> {
> - unsigned long flags;
> - asm volatile(
> - "mrs %0, daif // arch_local_save_flags"
> - : "=r" (flags)
> + unsigned long daif_bits;
> + unsigned long pmr; // Only used if alternative is on
> +
> + daif_bits = read_sysreg(daif);
> +
> + // Get PMR
> + asm volatile(ALTERNATIVE(
> + "nop",
> + "mrs_s %0, " __stringify(SYS_ICC_PMR_EL1),
> + ARM64_HAS_IRQ_PRIO_MASKING)
> + : "=&r" (pmr)

Why earlyclobber?

> :
> : "memory");

[...]

> @@ -85,16 +136,32 @@ static inline unsigned long arch_local_save_flags(void)

[...]

> 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)

Why earlyclobber? %0 is not written before the reading of any input
argument so far as I can see, in either alternative.

Cheers
---Dave
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