linux-kernel - Re: [PATCH v6 3/7] udmabuf: fix vmap

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Message-ID: <37e1f8a7-aa94-4a2b-9cd0-cb788a4f0b01@vivo.com>
Date: Fri, 13 Sep 2024 14:31:36 +0800
From: Huan Yang <link@...o.com>
To: "Kasireddy, Vivek" <vivek.kasireddy@...el.com>,
 Sumit Semwal <sumit.semwal@...aro.org>,
 Christian König <christian.koenig@....com>,
 Gerd Hoffmann <kraxel@...hat.com>,
 "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
 "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.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 v6 3/7] udmabuf: fix vmap_udmabuf error page set


在 2024/9/13 6:37, Kasireddy, Vivek 写道:
> Hi Huan,
>
>> Subject: [PATCH v6 3/7] udmabuf: fix vmap_udmabuf error page set
>>
>> 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.
>>
>> By this, we removed page usage in udmabuf totally.
>>
> I think this would probably need a Fixes tag:
> Fixes: 5e72b2b41a21 ("udmabuf: convert udmabuf driver to use folios")
OK, I'll update it
>
> Thanks,
> Vivek
>
>> Suggested-by: Vivek Kasireddy <vivek.kasireddy@...el.com>
>> Signed-off-by: Huan Yang <link@...o.com>
>> Acked-by: Vivek Kasireddy <vivek.kasireddy@...el.com>
>> ---
>>   drivers/dma-buf/Kconfig   |  1 +
>>   drivers/dma-buf/udmabuf.c | 22 +++++++++++++++-------
>>   2 files changed, 16 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/dma-buf/Kconfig b/drivers/dma-buf/Kconfig
>> index b46eb8a552d7..fee04fdb0822 100644
>> --- a/drivers/dma-buf/Kconfig
>> +++ b/drivers/dma-buf/Kconfig
>> @@ -36,6 +36,7 @@ config UDMABUF
>>   	depends on DMA_SHARED_BUFFER
>>   	depends on MEMFD_CREATE || COMPILE_TEST
>>   	depends on MMU
>> +	select VMAP_PFN
>>   	help
>>   	  A driver to let userspace turn memfd regions into dma-bufs.
>>   	  Qemu can use this to create host dmabufs for guest framebuffers.
>> diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
>> index ba9dbc7caf71..aa182a9dcdfa 100644
>> --- a/drivers/dma-buf/udmabuf.c
>> +++ b/drivers/dma-buf/udmabuf.c
>> @@ -103,21 +103,29 @@ 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;
>>   	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);
>> +	kvfree(pfns);
>>   	if (!vaddr)
>>   		return -EINVAL;
>>
>> --
>> 2.45.2