Re: [PATCH v2 3/4] fix vmap_udmabuf error page set

[Huan Yang <link@vivo.com>]

在 2024/8/10 10:39, Kasireddy, Vivek 写道:
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>
> Hi Huan,
>
>> 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.
>>
>> This patch fix it, set each folio's page correct, so that pages array
>> contains right page, and then map into vmalloc area
>>
>> Signed-off-by: Huan Yang <link@vivo.com>
>> ---
>>   drivers/dma-buf/udmabuf.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
>> index af2391cea0bf..9737f063b6b3 100644
>> --- a/drivers/dma-buf/udmabuf.c
>> +++ b/drivers/dma-buf/udmabuf.c
>> @@ -78,7 +78,8 @@ static int vmap_udmabuf(struct dma_buf *buf, struct
>> iosys_map *map)
>>                return -ENOMEM;
>>
>>        for (pg = 0; pg < ubuf->pagecount; pg++)
>> -             pages[pg] = &ubuf->folios[pg]->page;
>> +             pages[pg] = folio_page(ubuf->folios[pg],
>> +                                    ubuf->offsets[pg] >> PAGE_SHIFT);
> I believe the correct way to address this issue is to introduce a folio variant
> of vm_map_ram() and use that instead, along with the offsets info.
>
> However, for the time being, I think we can reject vmap of hugetlb folios
> by checking for non-zero offset values.

Do you mean, we do not want to vmap hugetlb folios?  So by check this is 
reasonable.

BTW, I found that recently shmem has started to support mTHP. (Even if 
need enable a switch)

If this, not only hugetlb contains large folio, so ignore offset may not 
too good?(I am not entirely sure whether mTHP can be used with shmem for 
memfd.)

Thanks.

>
> Thanks,
> Vivek
>
>>        vaddr = vm_map_ram(pages, ubuf->pagecount, -1);
>>        kvfree(pages);
>> --
>> 2.45.2