Re: [PATCHv4 2/2] arm64/io: Add a header for mmio access instrumentation

[Marc Zyngier]

On Mon, 15 Nov 2021 11:33:30 +0000,
Sai Prakash Ranjan <quic_saipraka@xxxxxxxxxxx> wrote:
> 
> The new generic header mmio-instrumented.h will keep arch code clean
> and separate from instrumented version which traces mmio register
> accesses. This instrumented header is generic and can be used by other
> architectures as well. Also add a generic flag (__DISABLE_TRACE_MMIO__)
> which is used to disable MMIO tracing in nVHE and if required can be
> used to disable tracing for specific drivers.
> 
> Signed-off-by: Sai Prakash Ranjan <quic_saipraka@xxxxxxxxxxx>
> ---
>  arch/arm64/include/asm/io.h       | 25 ++++-------
>  arch/arm64/kvm/hyp/nvhe/Makefile  |  2 +-
>  include/linux/mmio-instrumented.h | 70 +++++++++++++++++++++++++++++++
>  3 files changed, 80 insertions(+), 17 deletions(-)
>  create mode 100644 include/linux/mmio-instrumented.h
> 
> diff --git a/arch/arm64/include/asm/io.h b/arch/arm64/include/asm/io.h
> index 7fd836bea7eb..a635aaaf81b9 100644
> --- a/arch/arm64/include/asm/io.h
> +++ b/arch/arm64/include/asm/io.h
> @@ -10,6 +10,7 @@
>  
>  #include <linux/types.h>
>  #include <linux/pgtable.h>
> +#include <linux/mmio-instrumented.h>
>  
>  #include <asm/byteorder.h>
>  #include <asm/barrier.h>
> @@ -21,32 +22,27 @@
>  /*
>   * Generic IO read/write.  These perform native-endian accesses.
>   */
> -#define __raw_writeb __raw_writeb
> -static inline void __raw_writeb(u8 val, volatile void __iomem *addr)
> +static inline void arch_raw_writeb(u8 val, volatile void __iomem *addr)
>  {
>  	asm volatile("strb %w0, [%1]" : : "rZ" (val), "r" (addr));
>  }
>  
> -#define __raw_writew __raw_writew
> -static inline void __raw_writew(u16 val, volatile void __iomem *addr)
> +static inline void arch_raw_writew(u16 val, volatile void __iomem *addr)
>  {
>  	asm volatile("strh %w0, [%1]" : : "rZ" (val), "r" (addr));
>  }
>  
> -#define __raw_writel __raw_writel
> -static __always_inline void __raw_writel(u32 val, volatile void __iomem *addr)
> +static __always_inline void arch_raw_writel(u32 val, volatile void __iomem *addr)
>  {
>  	asm volatile("str %w0, [%1]" : : "rZ" (val), "r" (addr));
>  }
>  
> -#define __raw_writeq __raw_writeq
> -static inline void __raw_writeq(u64 val, volatile void __iomem *addr)
> +static inline void arch_raw_writeq(u64 val, volatile void __iomem *addr)
>  {
>  	asm volatile("str %x0, [%1]" : : "rZ" (val), "r" (addr));
>  }
>  
> -#define __raw_readb __raw_readb
> -static inline u8 __raw_readb(const volatile void __iomem *addr)
> +static inline u8 arch_raw_readb(const volatile void __iomem *addr)
>  {
>  	u8 val;
>  	asm volatile(ALTERNATIVE("ldrb %w0, [%1]",
> @@ -56,8 +52,7 @@ static inline u8 __raw_readb(const volatile void __iomem *addr)
>  	return val;
>  }
>  
> -#define __raw_readw __raw_readw
> -static inline u16 __raw_readw(const volatile void __iomem *addr)
> +static inline u16 arch_raw_readw(const volatile void __iomem *addr)
>  {
>  	u16 val;
>  
> @@ -68,8 +63,7 @@ static inline u16 __raw_readw(const volatile void __iomem *addr)
>  	return val;
>  }
>  
> -#define __raw_readl __raw_readl
> -static __always_inline u32 __raw_readl(const volatile void __iomem *addr)
> +static __always_inline u32 arch_raw_readl(const volatile void __iomem *addr)
>  {
>  	u32 val;
>  	asm volatile(ALTERNATIVE("ldr %w0, [%1]",
> @@ -79,8 +73,7 @@ static __always_inline u32 __raw_readl(const volatile void __iomem *addr)
>  	return val;
>  }
>  
> -#define __raw_readq __raw_readq
> -static inline u64 __raw_readq(const volatile void __iomem *addr)
> +static inline u64 arch_raw_readq(const volatile void __iomem *addr)
>  {
>  	u64 val;
>  	asm volatile(ALTERNATIVE("ldr %0, [%1]",
> diff --git a/arch/arm64/kvm/hyp/nvhe/Makefile b/arch/arm64/kvm/hyp/nvhe/Makefile
> index c3c11974fa3b..ff56d2165ea9 100644
> --- a/arch/arm64/kvm/hyp/nvhe/Makefile
> +++ b/arch/arm64/kvm/hyp/nvhe/Makefile
> @@ -4,7 +4,7 @@
>  #
>  
>  asflags-y := -D__KVM_NVHE_HYPERVISOR__ -D__DISABLE_EXPORTS
> -ccflags-y := -D__KVM_NVHE_HYPERVISOR__ -D__DISABLE_EXPORTS
> +ccflags-y := -D__KVM_NVHE_HYPERVISOR__ -D__DISABLE_EXPORTS -D__DISABLE_TRACE_MMIO__
>  
>  hostprogs := gen-hyprel
>  HOST_EXTRACFLAGS += -I$(objtree)/include
> diff --git a/include/linux/mmio-instrumented.h b/include/linux/mmio-instrumented.h
> new file mode 100644
> index 000000000000..99979c025cc1
> --- /dev/null
> +++ b/include/linux/mmio-instrumented.h
> @@ -0,0 +1,70 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (c) 2021 Qualcomm Innovation Center, Inc. All rights reserved.
> + */
> +
> +#ifndef _LINUX_MMIO_INSTRUMENTED_H
> +#define _LINUX_MMIO_INSTRUMENTED_H
> +
> +#include <linux/tracepoint-defs.h>
> +
> +/*
> + * Tracepoint and MMIO logging symbols should not be visible at EL2(HYP) as
> + * there is no way to execute them and any such MMIO access from EL2 will
> + * explode instantly (Words of Marc Zyngier). So introduce a generic flag
> + * __DISABLE_TRACE_MMIO__ to disable MMIO tracing in nVHE and other drivers
> + * if required.
> + */

This Gospel would be better placed next to the code that defines the
macro, given that this is an arch-independent include file, and hardly
anyone understands the quirks of a nVHE KVM (and only nVHE, something
that the comment fails to capture).

	M.

-- 
Without deviation from the norm, progress is not possible.