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Message-ID: <237db58a-18ad-b3ea-7559-3c22169cba26@huawei.com>
Date: Tue, 9 Jan 2024 10:34:15 +0800
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Subject: Re: [PATCH] swiotlb: check alloc_size before the allocation of a new
 memory pool
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To: Petr Tesarik <petr.tesarik1@huawei-partners.com>, <hch@lst.de>,
	<m.szyprowski@samsung.com>, <robin.murphy@arm.com>, <iommu@lists.linux.dev>,
	<linux-kernel@vger.kernel.org>
CC: <wangkefeng.wang@huawei.com>, <sunnanyong@huawei.com>
References: <20240108140005.3355316-1-zhangpeng362@huawei.com>
 <c68cfc31-317c-4709-a2e5-3729a137b1bb@huawei-partners.com>
From: "zhangpeng (AS)" <zhangpeng362@huawei.com>
In-Reply-To: <c68cfc31-317c-4709-a2e5-3729a137b1bb@huawei-partners.com>
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On 2024/1/8 23:46, Petr Tesarik wrote:

> On 1/8/2024 3:00 PM, Peng Zhang wrote:
>> From: ZhangPeng <zhangpeng362@huawei.com>
>>
>> The allocation request for swiotlb contiguous memory greater than
>> 128*2KB cannot be fulfilled because it exceeds the maximum contiguous
>> memory limit. If the swiotlb memory we allocate is larger than 128*2KB,
>> swiotlb_find_slots() will still schedule the allocation of a new memory
>> pool, which will increase memory overhead.
>>
>> Fix it by adding a check with alloc_size no more than 128*2KB before
>> scheduling the allocation of a new memory pool in swiotlb_find_slots().
>>
>> Signed-off-by: ZhangPeng <zhangpeng362@huawei.com>
>> ---
>>   kernel/dma/swiotlb.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
>> index 33d942615be5..cc92cff02c60 100644
>> --- a/kernel/dma/swiotlb.c
>> +++ b/kernel/dma/swiotlb.c
>> @@ -1126,6 +1126,9 @@ static int swiotlb_find_slots(struct device *dev, phys_addr_t orig_addr,
>>   	u64 phys_limit;
>>   	int index;
>>   
>> +	if (alloc_size > IO_TLB_SEGSIZE * IO_TLB_SIZE)
>> +		return -1;
>> +
>>   	rcu_read_lock();
>>   	list_for_each_entry_rcu(pool, &mem->pools, node) {
>>   		index = swiotlb_pool_find_slots(dev, pool, orig_addr,
> IIUC this such big allocations are not normally required by drivers, but
> I have already run into a similar issue with a Raspberry Pi 4 dma-buf
> object, so they can be triggered at will by user space. I also believe
> this sanity check is a good idea in general, not only when dynamic
> SWIOTLB is enabled.
>
> Reviewed-by: Petr Tesarik <petr.tesarik1@huawei-partners.com>
>
> Petr T

Thanks for your review!

-- 
Best Regards,
Peng