From: Aneesh Kumar K.V (IBM) <aneesh.kumar@kernel•org>
To: Nathan Lynch via B4 Relay
<devnull+nathanl.linux.ibm.com@kernel•org>,
Michael Ellerman <mpe@ellerman•id.au>,
Nicholas Piggin <npiggin@gmail•com>
Cc: "Nathan Lynch" <nathanl@linux•ibm.com>,
tyreld@linux•ibm.com, "Michal Suchánek" <msuchanek@suse•de>,
linuxppc-dev@lists•ozlabs.org, gcwilson@linux•ibm.com
Subject: Re: [PATCH v4 02/13] powerpc/rtas: Fall back to linear search on failed token->function lookup
Date: Mon, 20 Nov 2023 13:37:59 +0530 [thread overview]
Message-ID: <87il5wlue8.fsf@kernel.org> (raw)
In-Reply-To: <20231117-papr-sys_rtas-vs-lockdown-v4-2-b794d8cb8502@linux.ibm.com>
Nathan Lynch via B4 Relay <devnull+nathanl.linux.ibm.com@kernel•org>
writes:
> From: Nathan Lynch <nathanl@linux•ibm.com>
>
> Enabling any of the powerpc:rtas_* tracepoints at boot is likely to
> result in an oops on RTAS platforms. For example, booting a QEMU
> pseries model with 'trace_event=powerpc:rtas_input' in the command
> line leads to:
>
> BUG: Kernel NULL pointer dereference on read at 0x00000008
> Oops: Kernel access of bad area, sig: 7 [#1]
> NIP [c00000000004231c] do_enter_rtas+0x1bc/0x460
> LR [c00000000004231c] do_enter_rtas+0x1bc/0x460
> Call Trace:
> do_enter_rtas+0x1bc/0x460 (unreliable)
> rtas_call+0x22c/0x4a0
> rtas_get_boot_time+0x80/0x14c
> read_persistent_clock64+0x124/0x150
> read_persistent_wall_and_boot_offset+0x28/0x58
> timekeeping_init+0x70/0x348
> start_kernel+0xa0c/0xc1c
> start_here_common+0x1c/0x20
>
> (This is preceded by a warning for the failed lookup in
> rtas_token_to_function().)
>
> This happens when __do_enter_rtas_trace() attempts a token to function
> descriptor lookup before the xarray containing the mappings has been
> set up.
>
> Fall back to linear scan of the table if rtas_token_to_function_xarray
> is empty.
>
Reviewed-by: Aneesh Kumar K.V (IBM) <aneesh.kumar@kernel•org>
> Signed-off-by: Nathan Lynch <nathanl@linux•ibm.com>
> Fixes: 24098f580e2b ("powerpc/rtas: add tracepoints around RTAS entry")
> ---
> arch/powerpc/kernel/rtas.c | 18 ++++++++++++++----
> 1 file changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
> index 1ad1869e2e96..f0051881348a 100644
> --- a/arch/powerpc/kernel/rtas.c
> +++ b/arch/powerpc/kernel/rtas.c
> @@ -557,11 +557,21 @@ static const struct rtas_function *rtas_token_to_function(s32 token)
> return NULL;
>
> func = xa_load(&rtas_token_to_function_xarray, token);
> + if (func)
> + return func;
> + /*
> + * Fall back to linear scan in case the reverse mapping hasn't
> + * been initialized yet.
> + */
> + if (xa_empty(&rtas_token_to_function_xarray)) {
> + for_each_rtas_function(func) {
> + if (func->token == token)
> + return func;
> + }
> + }
>
> - if (WARN_ONCE(!func, "unexpected failed lookup for token %d", token))
> - return NULL;
> -
> - return func;
> + WARN_ONCE(true, "unexpected failed lookup for token %d", token);
> + return NULL;
> }
>
> /* This is here deliberately so it's only used in this file */
>
> --
> 2.41.0
next prev parent reply other threads:[~2023-11-20 20:19 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-18 5:14 [PATCH v4 00/13] powerpc/pseries: New character devices for system parameters and VPD Nathan Lynch via B4 Relay
2023-11-18 5:14 ` [PATCH v4 01/13] powerpc/rtas: Add for_each_rtas_function() iterator Nathan Lynch via B4 Relay
2023-11-20 8:07 ` Aneesh Kumar K.V
2023-11-18 5:14 ` [PATCH v4 02/13] powerpc/rtas: Fall back to linear search on failed token->function lookup Nathan Lynch via B4 Relay
2023-11-20 8:07 ` Aneesh Kumar K.V [this message]
2023-11-18 5:14 ` [PATCH v4 03/13] powerpc/rtas: Add function return status constants Nathan Lynch via B4 Relay
2023-11-20 8:08 ` Aneesh Kumar K.V
2023-11-18 5:14 ` [PATCH v4 04/13] powerpc/rtas: Factor out function descriptor lookup Nathan Lynch via B4 Relay
2023-11-20 8:08 ` Aneesh Kumar K.V
2023-11-18 5:14 ` [PATCH v4 05/13] powerpc/rtas: Facilitate high-level call sequences Nathan Lynch via B4 Relay
2023-11-20 8:10 ` Aneesh Kumar K.V
2023-11-28 15:35 ` Nathan Lynch
2023-11-28 22:30 ` Michael Ellerman
2023-11-28 23:05 ` Nathan Lynch
2023-11-29 13:20 ` Michael Ellerman
2023-11-30 18:26 ` Nathan Lynch
2023-11-30 21:41 ` Nathan Lynch
2023-11-30 22:46 ` Michael Ellerman
2023-11-30 23:53 ` Nathan Lynch
2023-12-05 16:51 ` Nathan Lynch
2023-12-07 1:02 ` Michael Ellerman
2023-11-29 2:11 ` Michael Ellerman
2023-11-29 2:37 ` Nathan Lynch
2023-11-29 3:16 ` Michael Ellerman
2023-11-18 5:14 ` [PATCH v4 06/13] powerpc/rtas: Serialize firmware activation sequences Nathan Lynch via B4 Relay
2023-11-20 8:12 ` Aneesh Kumar K.V
2023-11-28 15:32 ` Nathan Lynch
2023-11-28 15:46 ` Aneesh Kumar K.V
2023-11-28 16:16 ` Nathan Lynch
2023-11-28 16:41 ` Nathan Lynch
2023-11-18 5:14 ` [PATCH v4 07/13] powerpc/rtas: Warn if per-function lock isn't held Nathan Lynch via B4 Relay
2023-11-20 8:13 ` Aneesh Kumar K.V
2023-11-18 5:14 ` [PATCH v4 08/13] powerpc/uapi: Export papr-miscdev.h header Nathan Lynch via B4 Relay
2023-11-18 5:14 ` [PATCH v4 09/13] powerpc/pseries: Add papr-vpd character driver for VPD retrieval Nathan Lynch via B4 Relay
2023-11-21 8:31 ` Michal Suchánek
2023-11-28 15:38 ` Nathan Lynch
2023-11-29 2:07 ` Michael Ellerman
2023-11-29 2:41 ` Nathan Lynch
2023-11-29 3:13 ` Michael Ellerman
2023-11-18 5:14 ` [PATCH v4 10/13] powerpc/pseries/papr-sysparm: Validate buffer object lengths Nathan Lynch via B4 Relay
2023-11-18 5:14 ` [PATCH v4 11/13] powerpc/pseries/papr-sysparm: Expose character device to user space Nathan Lynch via B4 Relay
2023-11-18 5:14 ` [PATCH v4 12/13] powerpc/selftests: Add test for papr-vpd Nathan Lynch via B4 Relay
2023-11-18 5:14 ` [PATCH v4 13/13] powerpc/selftests: Add test for papr-sysparm Nathan Lynch via B4 Relay
2023-11-29 1:08 ` Michael Ellerman
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