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Message-ID: <20230919194337.GC424@noisy.programming.kicks-ass.net>
Date: Tue, 19 Sep 2023 21:43:37 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Dan Raymond <draymond@...valley.net>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org, tglx@...utronix.de,
mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
hpa@...or.com
Subject: Re: [PATCH v1] arch/x86: port I/O tracing on x86
On Mon, Sep 18, 2023 at 11:55:10AM -0600, Dan Raymond wrote:
> Add support for port I/O tracing on x86. Memory mapped I/O tracing is
> available on x86 via CONFIG_MMIOTRACE but that relies on page faults
> so it doesn't work with port I/O. This feature uses tracepoints in a
> similar manner as CONFIG_TRACE_MMIO_ACCESS.
>
> Signed-off-by: Dan Raymond <draymond@...valley.net>
> Suggested-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> ---
> arch/x86/include/asm/shared/io.h | 11 +++++++
> arch/x86/lib/Makefile | 1 +
> arch/x86/lib/trace_portio.c | 18 ++++++++++++
> include/trace/events/portio.h | 49 ++++++++++++++++++++++++++++++++
> 4 files changed, 79 insertions(+)
> create mode 100644 arch/x86/lib/trace_portio.c
> create mode 100644 include/trace/events/portio.h
>
> diff --git a/arch/x86/include/asm/shared/io.h b/arch/x86/include/asm/shared/io.h
> index c0ef921c0586..e7ef4212e00b 100644
> --- a/arch/x86/include/asm/shared/io.h
> +++ b/arch/x86/include/asm/shared/io.h
> @@ -2,13 +2,23 @@
> #ifndef _ASM_X86_SHARED_IO_H
> #define _ASM_X86_SHARED_IO_H
>
> +#include <linux/instruction_pointer.h>
> #include <linux/types.h>
>
> +#if defined(CONFIG_TRACEPOINTS) && !defined(BOOT_COMPRESSED_MISC_H) && !defined(BOOT_BOOT_H)
> +extern void do_trace_portio_read(u32 value, u16 port, char width, long ip_addr);
> +extern void do_trace_portio_write(u32 value, u16 port, char width, long ip_addr);
> +#else
> +static inline void do_trace_portio_read(u32 value, u16 port, char width, long ip_addr) {}
> +static inline void do_trace_portio_write(u32 value, u16 port, char width, long ip_addr) {}
> +#endif
> +
> #define BUILDIO(bwl, bw, type) \
> static inline void __out##bwl(type value, u16 port) \
> { \
> asm volatile("out" #bwl " %" #bw "0, %w1" \
> : : "a"(value), "Nd"(port)); \
> + do_trace_portio_write(value, port, #bwl[0], _THIS_IP_); \
> } \
> \
> static inline type __in##bwl(u16 port) \
> @@ -16,6 +26,7 @@ static inline type __in##bwl(u16 port) \
> type value; \
> asm volatile("in" #bwl " %w1, %" #bw "0" \
> : "=a"(value) : "Nd"(port)); \
> + do_trace_portio_read(value, port, #bwl[0], _THIS_IP_); \
> return value; \
> }
No, very much no.
This sticks tracing in the very rawest of raw output paths. This means I
can no longer use early_console->write() to print to my
early_serial_console.
That is the one and only fully reliably output path we have. You're not
sticking tracing in it.
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