linux-kernel - Re: [PATCH v1 1/1] powerpc/papr_scm: Properly handle UUID types and API

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Message-ID: <266684c6-e2c8-e19b-214d-809f16e79e7b@linux.ibm.com>
Date:   Fri, 16 Apr 2021 10:08:45 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Vaibhav Jain <vaibhav@...ux.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        "Oliver O'Halloran" <oohall@...il.com>
Subject: Re: [PATCH v1 1/1] powerpc/papr_scm: Properly handle UUID types and
 API

On 4/15/21 7:16 PM, Andy Shevchenko wrote:
> Parse to and export from UUID own type, before dereferencing.
> This also fixes wrong comment (Little Endian UUID is something else)
> and should fix Sparse warnings about assigning strict types to POD.
> 

I am wondering whether this will break older namespace created. IIRC 
that cpu_to_le64 was done to be backward compatible with namespaces 
created before 259a948c4ba1.

What we need to test is create a namespace in little endian kernel and 
read it back in via big endian and vice versa. Also we need to make sure 
we can read the already created namespace before this patch.


> Fixes: 43001c52b603 ("powerpc/papr_scm: Use ibm,unit-guid as the iset cookie")
> Fixes: 259a948c4ba1 ("powerpc/pseries/scm: Use a specific endian format for storing uuid from the device tree")
> Cc: Oliver O'Halloran <oohall@...il.com>
> Cc: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> ---
> Not tested
>   arch/powerpc/platforms/pseries/papr_scm.c | 13 ++++++++-----
>   1 file changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/pseries/papr_scm.c b/arch/powerpc/platforms/pseries/papr_scm.c
> index ae6f5d80d5ce..4366e1902890 100644
> --- a/arch/powerpc/platforms/pseries/papr_scm.c
> +++ b/arch/powerpc/platforms/pseries/papr_scm.c
> @@ -1085,8 +1085,9 @@ static int papr_scm_probe(struct platform_device *pdev)
>   	u32 drc_index, metadata_size;
>   	u64 blocks, block_size;
>   	struct papr_scm_priv *p;
> +	u8 uuid_raw[UUID_SIZE];
>   	const char *uuid_str;
> -	u64 uuid[2];
> +	uuid_t uuid;
>   	int rc;
>   
>   	/* check we have all the required DT properties */
> @@ -1129,16 +1130,18 @@ static int papr_scm_probe(struct platform_device *pdev)
>   	p->hcall_flush_required = of_property_read_bool(dn, "ibm,hcall-flush-required");
>   
>   	/* We just need to ensure that set cookies are unique across */
> -	uuid_parse(uuid_str, (uuid_t *) uuid);
> +	uuid_parse(uuid_str, &uuid);
> +
>   	/*
>   	 * cookie1 and cookie2 are not really little endian
> -	 * we store a little endian representation of the
> +	 * we store a raw buffer representation of the
>   	 * uuid str so that we can compare this with the label
>   	 * area cookie irrespective of the endian config with which
>   	 * the kernel is built.
>   	 */
> -	p->nd_set.cookie1 = cpu_to_le64(uuid[0]);
> -	p->nd_set.cookie2 = cpu_to_le64(uuid[1]);
> +	export_uuid(uuid_raw, &uuid);
> +	p->nd_set.cookie1 = get_unaligned_le64(&uuid_raw[0]);
> +	p->nd_set.cookie2 = get_unaligned_le64(&uuid_raw[8]);
>   
>   	/* might be zero */
>   	p->metadata_size = metadata_size;
>