linux-kernel - Re: [PATCH v3 3/5] fix vmap

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Message-ID: <e5569c9c-c38e-4011-b77e-31a4df065cb7@vivo.com>
Date: Tue, 20 Aug 2024 09:33:44 +0800
From: Huan Yang <link@...o.com>
To: "Kasireddy, Vivek" <vivek.kasireddy@...el.com>,
 Gerd Hoffmann <kraxel@...hat.com>, Sumit Semwal <sumit.semwal@...aro.org>,
 Christian König <christian.koenig@....com>,
 "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
 "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
 "linaro-mm-sig@...ts.linaro.org" <linaro-mm-sig@...ts.linaro.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc: "opensource.kernel@...o.com" <opensource.kernel@...o.com>
Subject: Re: [PATCH v3 3/5] fix vmap_udmabuf error page set


在 2024/8/17 8:54, Kasireddy, Vivek 写道:
> Hi Huan,
>
>> Subject: [PATCH v3 3/5] fix vmap_udmabuf error page set
> Please prepend a "udmabuf:" to the subject line and improve the wording.
OK, sorry for this mistake.
>
>> Currently vmap_udmabuf set page's array by each folio.
>> But, ubuf->folios is only contain's the folio's head page.
>>
>> That mean we repeatedly mapped the folio head page to the vmalloc area.
>>
>> Due to udmabuf can use hugetlb, if HVO enabled, tail page may not exist,
>> so, we can't use page array to map, instead, use pfn array.
>>
>> Signed-off-by: Huan Yang <link@...o.com>
>> Suggested-by: Vivek Kasireddy <vivek.kasireddy@...el.com>
>> ---
>>   drivers/dma-buf/udmabuf.c | 22 +++++++++++++++-------
>>   1 file changed, 15 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
>> index 3ec72d47bb1c..4ec54c60d76c 100644
>> --- a/drivers/dma-buf/udmabuf.c
>> +++ b/drivers/dma-buf/udmabuf.c
>> @@ -67,21 +67,29 @@ static int mmap_udmabuf(struct dma_buf *buf,
>> struct vm_area_struct *vma)
>>   static int vmap_udmabuf(struct dma_buf *buf, struct iosys_map *map)
>>   {
>>   	struct udmabuf *ubuf = buf->priv;
>> -	struct page **pages;
>> +	unsigned long *pfns;
> I wish there was a way to easily test the vmap scenario but its great that

It need a driver set in kernel. maybe write a debug code in udmabuf?(not 
sure)

> you are able to eliminate the usage of "struct page" completely from
> udmabuf driver, with this patch.
>
>>   	void *vaddr;
>>   	pgoff_t pg;
>>
>>   	dma_resv_assert_held(buf->resv);
>>
>> -	pages = kvmalloc_array(ubuf->pagecount, sizeof(*pages),
>> GFP_KERNEL);
>> -	if (!pages)
>> +	/**
>> +	 * HVO may free tail pages, so just use pfn to map each folio
>> +	 * into vmalloc area.
>> +	 */
>> +	pfns = kvmalloc_array(ubuf->pagecount, sizeof(*pfns), GFP_KERNEL);
>> +	if (!pfns)
>>   		return -ENOMEM;
>>
>> -	for (pg = 0; pg < ubuf->pagecount; pg++)
>> -		pages[pg] = &ubuf->folios[pg]->page;
>> +	for (pg = 0; pg < ubuf->pagecount; pg++) {
>> +		unsigned long pfn = folio_pfn(ubuf->folios[pg]);
>>
>> -	vaddr = vm_map_ram(pages, ubuf->pagecount, -1);
>> -	kvfree(pages);
>> +		pfn += ubuf->offsets[pg] >> PAGE_SHIFT;
>> +		pfns[pg] = pfn;
>> +	}
>> +
>> +	vaddr = vmap_pfn(pfns, ubuf->pagecount, PAGE_KERNEL);
> Looks like this would require a "select VMAP_PFN" in Kconfig.

Yes, I miss this.

Thank you too much.

>
> Thanks,
> Vivek
>
>> +	kvfree(pfns);
>>   	if (!vaddr)
>>   		return -EINVAL;
>>
>> --
>> 2.45.2