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SubjectRe: [PATCH v10 12/25] arm64: irqflags: Use ICC_PMR_EL1 for interrupt masking
On Thu, Jan 31, 2019 at 02:58:50PM +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>
> Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> 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 | 100 +++++++++++++++++++++++++++-----------
> 2 files changed, 83 insertions(+), 28 deletions(-)
>
> diff --git a/arch/arm64/include/asm/efi.h b/arch/arm64/include/asm/efi.h
> index 7ed3208..c9e9a69 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)
>
> +/*
> + * Even when Linux uses IRQ priorities for IRQ disabling, EFI does not.
> + * And EFI shouldn't really play around with priority masking as it is not aware
> + * which priorities the OS has assigned to its interrupts.
> + */
> +#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 */
>
> /*
> diff --git a/arch/arm64/include/asm/irqflags.h b/arch/arm64/include/asm/irqflags.h
> index 24692ed..d4597b2 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 +38,27 @@
> /*
> * 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"
> - :
> + 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" (GIC_PRIO_IRQON)
> : "memory");
> }
>
> static inline void arch_local_irq_disable(void)
> {
> - asm volatile(
> - "msr daifset, #2 // arch_local_irq_disable"
> - :
> + asm volatile(ALTERNATIVE(
> + "msr daifset, #2 // arch_local_irq_disable",
> + "msr_s " __stringify(SYS_ICC_PMR_EL1) ", %0",
> + ARM64_HAS_IRQ_PRIO_MASKING)
> :
> + : "r" (GIC_PRIO_IRQOFF)
> : "memory");
> }
>
> @@ -71,12 +67,44 @@ 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 +113,32 @@ 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
>

Hi Julien,

This patch introduced a slew of Clang warnings:

In file included from arch/arm64/kernel/signal.c:21:
In file included from include/linux/compat.h:10:
In file included from include/linux/time.h:6:
In file included from include/linux/seqlock.h:36:
In file included from include/linux/spinlock.h:54:
In file included from include/linux/irqflags.h:16:
arch/arm64/include/asm/irqflags.h:50:10: warning: value size does not match register size specified by the constraint and modifier [-Wasm-operand-widths]
: "r" (GIC_PRIO_IRQON)
^
arch/arm64/include/asm/ptrace.h:39:25: note: expanded from macro 'GIC_PRIO_IRQON'
#define GIC_PRIO_IRQON 0xf0
^
arch/arm64/include/asm/irqflags.h:46:44: note: use constraint modifier "w"
"msr_s " __stringify(SYS_ICC_PMR_EL1) ",%0\n"
^~
%w0
arch/arm64/include/asm/alternative.h:286:29: note: expanded from macro 'ALTERNATIVE'
_ALTERNATIVE_CFG(oldinstr, newinstr, __VA_ARGS__, 1)
^
arch/arm64/include/asm/alternative.h:88:30: note: expanded from macro '_ALTERNATIVE_CFG'
__ALTERNATIVE_CFG(oldinstr, newinstr, feature, IS_ENABLED(cfg), 0)
^
arch/arm64/include/asm/alternative.h:76:2: note: expanded from macro '__ALTERNATIVE_CFG'
newinstr "\n" \
^
In file included from arch/arm64/kernel/signal.c:21:
In file included from include/linux/compat.h:10:
In file included from include/linux/time.h:6:
In file included from include/linux/seqlock.h:36:
In file included from include/linux/spinlock.h:54:
In file included from include/linux/irqflags.h:16:
arch/arm64/include/asm/irqflags.h:61:10: warning: value size does not match register size specified by the constraint and modifier [-Wasm-operand-widths]
: "r" (GIC_PRIO_IRQOFF)
^
arch/arm64/include/asm/ptrace.h:40:26: note: expanded from macro 'GIC_PRIO_IRQOFF'
#define GIC_PRIO_IRQOFF (GIC_PRIO_IRQON & ~0x80)
^
arch/arm64/include/asm/irqflags.h:58:45: note: use constraint modifier "w"
"msr_s " __stringify(SYS_ICC_PMR_EL1) ", %0",
^
arch/arm64/include/asm/irqflags.h:94:10: warning: value size does not match register size specified by the constraint and modifier [-Wasm-operand-widths]
: "r" (GIC_PRIO_IRQOFF)
^
arch/arm64/include/asm/ptrace.h:40:26: note: expanded from macro 'GIC_PRIO_IRQOFF'
#define GIC_PRIO_IRQOFF (GIC_PRIO_IRQON & ~0x80)
^
arch/arm64/include/asm/irqflags.h:91:18: note: use constraint modifier "w"
"csel %0, %0, %2, eq",
^~
%w2
arch/arm64/include/asm/alternative.h:286:29: note: expanded from macro 'ALTERNATIVE'
_ALTERNATIVE_CFG(oldinstr, newinstr, __VA_ARGS__, 1)
^
arch/arm64/include/asm/alternative.h:88:30: note: expanded from macro '_ALTERNATIVE_CFG'
__ALTERNATIVE_CFG(oldinstr, newinstr, feature, IS_ENABLED(cfg), 0)
^
arch/arm64/include/asm/alternative.h:76:2: note: expanded from macro '__ALTERNATIVE_CFG'
newinstr "\n" \
^
3 warnings generated.

I am not sure if they should be fixed with Clang's suggestion of a
constraint modifier or a cast like commit 1b57ec8c7527 ("arm64: io:
Ensure value passed to __iormb() is held in a 64-bit register"), hence
this message.

Thanks,
Nathan

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