linux-kernel - Re: [PATCH] powerpc/mm: fix a hardcode on memory boundary checking

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Message-Id: <a97db3cd-a756-390c-505e-819718b64904@linux.vnet.ibm.com>
Date:   Mon, 6 Feb 2017 10:50:21 +0800
From:   Rui Teng <rui.teng@...ux.vnet.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Cc:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        jia he <hejianet@...ux.vnet.ibm.com>
Subject: Re: [PATCH] powerpc/mm: fix a hardcode on memory boundary checking

On 31/01/2017 5:11 PM, Michael Ellerman wrote:
> Rui Teng <rui.teng@...ux.vnet.ibm.com> writes:
>
>> The offset of hugepage block will not be 16G, if the expected
>> page is more than one. Calculate the totol size instead of the
>> hardcode value.
>
> I assume you found this by code inspection and not by triggering an
> actual bug?

Yes, I found this problem only by code inspection. We were finding the
ways to enable 16G huge page besides changing the device tree. For 
example, provide a new interface to set these size and pages parameters.
So that I think it may cause problem here.

>
> cheers
>
>> diff --git a/arch/powerpc/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c
>> index 8033493..b829f8e 100644
>> --- a/arch/powerpc/mm/hash_utils_64.c
>> +++ b/arch/powerpc/mm/hash_utils_64.c
>> @@ -506,7 +506,7 @@ static int __init htab_dt_scan_hugepage_blocks(unsigned long node,
>>  	printk(KERN_INFO "Huge page(16GB) memory: "
>>  			"addr = 0x%lX size = 0x%lX pages = %d\n",
>>  			phys_addr, block_size, expected_pages);
>> -	if (phys_addr + (16 * GB) <= memblock_end_of_DRAM()) {
>> +	if (phys_addr + block_size * expected_pages <= memblock_end_of_DRAM()) {
>>  		memblock_reserve(phys_addr, block_size * expected_pages);
>>  		add_gpage(phys_addr, block_size, expected_pages);
>>  	}
>> --
>> 2.9.0
>