linux-kernel - RE: [PATCH V2 4/4] misc: vop: mapping kernel memory to user space as noncached

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Message-ID: <VI1PR04MB4960D01FB5508589D586AE5792320@VI1PR04MB4960.eurprd04.prod.outlook.com>
Date:   Tue, 29 Sep 2020 13:12:43 +0000
From:   Sherry Sun <sherry.sun@....com>
To:     Christoph Hellwig <hch@...radead.org>
CC:     "sudeep.dutt@...el.com" <sudeep.dutt@...el.com>,
        "ashutosh.dixit@...el.com" <ashutosh.dixit@...el.com>,
        "arnd@...db.de" <arnd@...db.de>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "kishon@...com" <kishon@...com>,
        "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: RE: [PATCH V2 4/4] misc: vop: mapping kernel memory to user space as
 noncached

Hi Christoph,

> On Tue, Sep 29, 2020 at 04:44:25PM +0800, Sherry Sun wrote:
> > Mapping kernel space memory to user space as noncached, since user
> > space need check the updates of avail_idx and device page flags timely.
> >
> > Signed-off-by: Joakim Zhang <qiangqing.zhang@....com>
> > Signed-off-by: Sherry Sun <sherry.sun@....com>
> > ---
> >  drivers/misc/mic/vop/vop_vringh.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/misc/mic/vop/vop_vringh.c
> > b/drivers/misc/mic/vop/vop_vringh.c
> > index 4d5feb39aeb7..6e193bd64ef1 100644
> > --- a/drivers/misc/mic/vop/vop_vringh.c
> > +++ b/drivers/misc/mic/vop/vop_vringh.c
> > @@ -1057,7 +1057,7 @@ static int vop_mmap(struct file *f, struct
> vm_area_struct *vma)
> >  		}
> >  		err = remap_pfn_range(vma, vma->vm_start + offset,
> >  				      pa >> PAGE_SHIFT, size,
> > -				      vma->vm_page_prot);
> > +				      pgprot_noncached(vma->vm_page_prot));
> 
> You can't call remap_pfn_range on memory returned from
> dma_alloc_coherent (which btw is not marked uncached on many platforms).
> 
> You need to use the dma_mmap_coherent helper instead.  And this also
> needs to go into the first patch.

Okay, will try to use dma_mmap_coherent  api in V3. Thanks.

Regards
Sherry