linux-kernel - Re: [PATCH] pseries/energy: Use OF accessor functions to read ibm,drc-indexes

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Message-Id: <20190308160106.GA5263@drishya.in.ibm.com>
Date:   Fri, 8 Mar 2019 21:31:06 +0530
From:   Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
To:     "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
Cc:     Michael Bringmann <mwb@...ux.vnet.ibm.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        "Pavithra R. Prakash" <pavrampu@...ibm.com>, stable@...r.kernel.org
Subject: Re: [PATCH] pseries/energy: Use OF accessor functions to read
 ibm,drc-indexes

* Gautham R Shenoy <ego@...ux.vnet.ibm.com> [2019-03-08 21:03:24]:

> From: "Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>
> 
> In cpu_to_drc_index() in the case when FW_FEATURE_DRC_INFO is absent,
> we currently use of_read_property() to obtain the pointer to the array
> corresponding to the property "ibm,drc-indexes". The elements of this
> array are of type __be32, but are accessed without any conversion to
> the OS-endianness, which is buggy on a Little Endian OS.
> 
> Fix this by using of_property_read_u32_index() accessor function to
> safely read the elements of the array.
> 
> Fixes: commit e83636ac3334 ("pseries/drc-info: Search DRC properties for CPU indexes")
> Cc: <stable@...r.kernel.org> #v4.16+
> Reported-by: Pavithra R. Prakash <pavrampu@...ibm.com>
> Signed-off-by: Gautham R. Shenoy <ego@...ux.vnet.ibm.com>

Reviewed-by: Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>

> ---
>  arch/powerpc/platforms/pseries/pseries_energy.c | 27 ++++++++++++++++---------
>  1 file changed, 18 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/pseries/pseries_energy.c b/arch/powerpc/platforms/pseries/pseries_energy.c
> index 6ed2212..1c4d1ba 100644
> --- a/arch/powerpc/platforms/pseries/pseries_energy.c
> +++ b/arch/powerpc/platforms/pseries/pseries_energy.c
> @@ -77,18 +77,27 @@ static u32 cpu_to_drc_index(int cpu)
> 
>  		ret = drc.drc_index_start + (thread_index * drc.sequential_inc);
>  	} else {
> -		const __be32 *indexes;
> -
> -		indexes = of_get_property(dn, "ibm,drc-indexes", NULL);
> -		if (indexes == NULL)
> -			goto err_of_node_put;
> +		u32 nr_drc_indexes, thread_drc_index;
> 
>  		/*
> -		 * The first element indexes[0] is the number of drc_indexes
> -		 * returned in the list.  Hence thread_index+1 will get the
> -		 * drc_index corresponding to core number thread_index.
> +		 * The first element of ibm,drc-indexes array is the
> +		 * number of drc_indexes returned in the list.  Hence
> +		 * thread_index+1 will get the drc_index corresponding
> +		 * to core number thread_index.
>  		 */
> -		ret = indexes[thread_index + 1];
> +		rc = of_property_read_u32_index(dn, "ibm,drc-indexes",
> +						0, &nr_drc_indexes);
> +		if (rc)
> +			goto err_of_node_put;
> +
> +		WARN_ON(thread_index > nr_drc_indexes);
> +		rc = of_property_read_u32_index(dn, "ibm,drc-indexes",
> +						thread_index + 1,
> +						&thread_drc_index);
> +		if (rc)
> +			goto err_of_node_put;
> +
> +		ret = thread_drc_index;

Oops!  Good bugfix.  We should use device tree accessors like this in
all places for correct and safe code.

Thanks!

--Vaidy