linux-kernel - Re: [RFC PATCH v2 2/3] pstore: Add register read/write{b,w,l,q} tracing support

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Date:   Fri, 24 Aug 2018 08:29:46 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Laura Abbott <labbott@...hat.com>,
        Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Jason Baron <jbaron@...mai.com>,
        Tony Luck <tony.luck@...el.com>, Arnd Bergmann <arnd@...db.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Joe Perches <joe@...ches.com>,
        Jim Cromie <jim.cromie@...il.com>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Vivek Gautam <vivek.gautam@...eaurora.org>,
        Sibi Sankar <sibis@...eaurora.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-arm-msm@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Tom Zanussi <tom.zanussi@...ux.intel.com>
Subject: Re: [RFC PATCH v2 2/3] pstore: Add register read/write{b,w,l,q}
 tracing support

On Fri, Aug 24, 2018 at 7:45 AM, Sai Prakash Ranjan
<saiprakash.ranjan@...eaurora.org> wrote:
> read/write{b,w,l,q} are typically used for reading from memory
> mapped registers, which can cause hangs if accessed
> unclocked. Tracing these events can help in debugging
> various issues faced during initial development.
>
> We log this trace information in persistent ram buffer which
> can be viewed after reset.
>
> We use pstore_rtb_call() to write the RTB log to pstore.
> RTB buffer size is taken from ramoops dt node with additional
> property called rtb-size.
>
> For reading the trace after mounting pstore, rtb-ramoops entry
> can be seen in /sys/fs/pstore/ as in below sample output.
>
> Sample output of tracing register reads/writes in drivers:
>
>  # mount -t pstore pstore /sys/fs/pstore
>  # tail /sys/fs/pstore/rtb-ramoops-0
>  [LOGK_READ ] ts:36468476204  data:ffff00000800d0fc  <ffff0000084e9ee0>  gic_check_gicv2+0x58/0x60
>  [LOGK_WRITE] ts:36468477715  data:ffff00000800d000  <ffff0000084e9fac>  gic_cpu_if_up+0xc4/0x110
>  [LOGK_READ ] ts:36468478548  data:ffff00000800d000  <ffff0000084e9fd8>  gic_cpu_if_up+0xf0/0x110
>  [LOGK_WRITE] ts:36468480319  data:ffff00000800d000  <ffff0000084e9fac>  gic_cpu_if_up+0xc4/0x110
>  [LOGK_READ ] ts:36468481048  data:ffff00000800d00c  <ffff000008081a34>  gic_handle_irq+0xac/0x128
>  [LOGK_WRITE] ts:36468482923  data:ffff00000800d010  <ffff000008081aac>  gic_handle_irq+0x124/0x128
>  [LOGK_READ ] ts:36468483184  data:ffff00000800d00c  <ffff000008081a34>  gic_handle_irq+0xac/0x128
>  [LOGK_WRITE] ts:36468485215  data:ffff00000800d010  <ffff000008081aac>  gic_handle_irq+0x124/0x128
>  [LOGK_READ ] ts:36468486309  data:ffff00000800d00c  <ffff000008081a34>  gic_handle_irq+0xac/0x128
>  [LOGK_WRITE] ts:36468488236  data:ffff00000800d010  <ffff000008081aac>  gic_handle_irq+0x124/0x128
>
> Output has below 5 fields:
>
>  * Log type, Timestamp, Data from caller which is the address of
>    read/write{b,w,l,q}, Caller ip and Caller name.
>
> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>

As this is a tracing-like method, could this instead be added to
ftrace? That would mean it could reuse all the ftrace tools and you'd
get pstore storage for free.

-Kees

-- 
Kees Cook
Pixel Security