Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Mime-Version: 1.0
Subject: RE: [PATCH v3] dma-buf/heaps: system_heap: avoid too much
 allocation
Reply-To: jaewon31.kim@samsung.com
Sender: Jaewon Kim <jaewon31.kim@samsung.com>
From:   Jaewon Kim <jaewon31.kim@samsung.com>
To:     Michal Hocko <mhocko@suse.com>
CC:     "jstultz@google.com" <jstultz@google.com>,
        "tjmercier@google.com" <tjmercier@google.com>,
        "sumit.semwal@linaro.org" <sumit.semwal@linaro.org>,
        "daniel.vetter@ffwll.ch" <daniel.vetter@ffwll.ch>,
        "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
        "hannes@cmpxchg.org" <hannes@cmpxchg.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "jaewon31.kim@gmail.com" <jaewon31.kim@gmail.com>
In-Reply-To: <ZDZqYTSHBNGLq0zI@dhcp22.suse.cz>
Message-ID: <20230412085726epcms1p7d2bec2526e47bd10a3b6ea6a113c9cc3@epcms1p7>
Date:   Wed, 12 Apr 2023 17:57:26 +0900
Content-Transfer-Encoding: 7bit
Content-Type: text/plain; charset="utf-8"
CMS-TYPE: 101P
DLP-Filter: Pass
References: <ZDZqYTSHBNGLq0zI@dhcp22.suse.cz>
        <20230410073228.23043-1-jaewon31.kim@samsung.com>
        <CGME20230410073304epcas1p4cf3079b096994d69472b7801bd530bc7@epcms1p7>
Precedence: bulk

>Sorry for being late. I know there was some pre-existing discussion
>around that but I didn't have time to participate.
>
>On Mon 10-04-23 16:32:28, Jaewon Kim wrote:
>> @@ -350,6 +350,9 @@ static struct dma_buf *system_heap_allocate(struct dma_heap *heap,
>>  	struct page *page, *tmp_page;
>>  	int i, ret = -ENOMEM;
>>  
>> +	if (len / PAGE_SIZE > totalram_pages())
>> +		return ERR_PTR(-ENOMEM);
>> +
>
>This is an antipattern imho. Check 7661809d493b ("mm: don't allow
>oversized kvmalloc() calls") how kvmalloc has dealt with a similar

Hello Thank you for the information.

I tried to search the macro of INT_MAX.

include/vdso/limits.h
#define INT_MAX         ((int)(~0U >> 1))

AFAIK the dma-buf system heap user can request that huge size more than 2GB. So
I think totalram_pages() is better than INT_MAX in this case.

>issue. totalram_pages doesn't really tell you anything about incorrect
>users. You might be on a low memory system where the request size is
>sane normally, it just doesn't fit into memory on that particular
>machine.

Sorry maybe I'm not fully understand what you meant. User may requested
a huge size like 3GB on 2GB ram device. But I think that should be rejected
because it is bigger than the device ram size.

Jaewon Kim

>
>
>>  	buffer = kzalloc(sizeof(*buffer), GFP_KERNEL);
>>  	if (!buffer)
>>  		return ERR_PTR(-ENOMEM);
>> -- 
>> 2.17.1
>
>-- 
>Michal Hocko
>SUSE Labs