linux-kernel - Re: [PATCH] powerpc/pkeys: Fix reading of ibm,processor-storage-keys property

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Date:   Thu, 20 Sep 2018 09:11:47 -0700
From:   Ram Pai <linuxram@...ibm.com>
To:     Thiago Jung Bauermann <bauerman@...ux.ibm.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH] powerpc/pkeys: Fix reading of ibm,processor-storage-keys
 property

On Thu, Sep 20, 2018 at 01:38:58AM -0300, Thiago Jung Bauermann wrote:
> scan_pkey_feature() uses of_property_read_u32_array() to read the
> ibm,processor-storage-keys property and calls be32_to_cpu() on the
> value it gets. The problem is that of_property_read_u32_array() already
> returns the value converted to the CPU byte order.
> 
> The value of pkeys_total ends up more or less sane because there's a min()
> call in pkey_initialize() which reduces pkeys_total to 32. So in practice
> the kernel ignores the fact that the hypervisor reserved one key for
> itself (the device tree advertises 31 keys in my test VM).
> 
> This is wrong, but the effect in practice is that when a process tries to
> allocate the 32nd key, it gets an -EINVAL error instead of -ENOSPC which
> would indicate that there aren't any keys available

Thanks for the fix.

Reviewed-by: Ram Pai <linuxram@...ibm.com>

> 
> Fixes: cf43d3b26452 ("powerpc: Enable pkey subsystem")
> Signed-off-by: Thiago Jung Bauermann <bauerman@...ux.ibm.com>
> ---
>  arch/powerpc/mm/pkeys.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/mm/pkeys.c b/arch/powerpc/mm/pkeys.c
> index 333b1f80c435..b271b283c785 100644
> --- a/arch/powerpc/mm/pkeys.c
> +++ b/arch/powerpc/mm/pkeys.c
> @@ -45,7 +45,7 @@ static void scan_pkey_feature(void)
>  	 * Since any pkey can be used for data or execute, we will just treat
>  	 * all keys as equal and track them as one entity.
>  	 */
> -	pkeys_total = be32_to_cpu(vals[0]);
> +	pkeys_total = vals[0];
>  	pkeys_devtree_defined = true;
>  }

-- 
Ram Pai