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

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Date:   Thu, 18 Nov 2021 16:24:48 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Sai Prakash Ranjan <quic_saipraka@...cinc.com>
Cc:     Will Deacon <will@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Catalin Marinas <catalin.marinas@....com>,
        quic_psodagud@...cinc.com, Marc Zyngier <maz@...nel.org>,
        gregkh <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCHv4 2/2] arm64/io: Add a header for mmio access instrumentation

On Mon, Nov 15, 2021 at 12:33 PM Sai Prakash Ranjan
<quic_saipraka@...cinc.com> wrote:
>  /*
>   * 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));
>  }

Woundn't removing the #define here will break the logic in
include/asm-generic/io.h,
making it fall back to the pointer-dereference version for the actual access?

> +#if IS_ENABLED(CONFIG_TRACE_MMIO_ACCESS) && !(defined(__DISABLE_TRACE_MMIO__))
> +DECLARE_TRACEPOINT(rwmmio_write);
> +DECLARE_TRACEPOINT(rwmmio_read);
> +
> +void log_write_mmio(const char *width, volatile void __iomem *addr);
> +void log_read_mmio(const char *width, const volatile void __iomem *addr);
> +
> +#define __raw_write(v, a, _l)  ({                              \
> +       volatile void __iomem *_a = (a);                        \
> +       if (tracepoint_enabled(rwmmio_write))                   \
> +               log_write_mmio(__stringify(write##_l), _a);     \
> +       arch_raw_write##_l((v), _a);                            \
> +       })

This feels like it's getting too big to be inlined. Have you considered
integrating this with the lib/logic_iomem.c infrastructure instead?

That already provides a way to override MMIO areas, and it lets you do
the logging from a single place rather than having it duplicated in every
single caller. It also provides a way of filtering it based on the ioremap()
call.

        Arnd