linux-kernel - Re: [PATCH v2] fpga: dfl: afu: convert get_user_pages() --> pin_user

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Message-ID: <20200523205717.GA443638@epycbox.lan>
Date:   Sat, 23 May 2020 13:57:17 -0700
From:   Moritz Fischer <mdf@...nel.org>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, Xu Yilun <yilun.xu@...el.com>,
        Wu Hao <hao.wu@...el.com>, Moritz Fischer <mdf@...nel.org>,
        linux-fpga@...r.kernel.org
Subject: Re: [PATCH v2] fpga: dfl: afu: convert get_user_pages() -->
 pin_user_pages()

On Fri, May 22, 2020 at 06:52:34PM -0700, John Hubbard wrote:
> On 2020-05-19 13:14, John Hubbard wrote:
> > This code was using get_user_pages_fast(), in a "Case 2" scenario
> > (DMA/RDMA), using the categorization from [1]. That means that it's
> > time to convert the get_user_pages_fast() + put_page() calls to
> > pin_user_pages_fast() + unpin_user_pages() calls.
> > 
> > There is some helpful background in [2]: basically, this is a small
> > part of fixing a long-standing disconnect between pinning pages, and
> > file systems' use of those pages.
> > 
> > [1] Documentation/core-api/pin_user_pages.rst
> > 
> > [2] "Explicit pinning of user-space pages":
> >      https://lwn.net/Articles/807108/
> > 
> > Cc: Xu Yilun <yilun.xu@...el.com>
> > Cc: Wu Hao <hao.wu@...el.com>
> > Cc: Moritz Fischer <mdf@...nel.org>
> > Cc: linux-fpga@...r.kernel.org
> > Signed-off-by: John Hubbard <jhubbard@...dia.com>
> 
> 
> Hi Moritz and FPGA developers,
> 
> Is this OK? And if so, is it going into your git tree? Or should I
> send it up through a different tree? (I'm new to the FPGA development
> model).

I can take it, sorry for sluggish response.

Cheers,
Moritz

> 
> 
> thanks,
> -- 
> John Hubbard
> NVIDIA
> 
> 
> 
> > ---
> > 
> > Hi,
> > 
> > Changes since v1:
> > 
> > Changed the label from "put_pages", to "unpin_pages".
> > 
> > thanks,
> > John Hubbard
> > NVIDIA
> >   drivers/fpga/dfl-afu-dma-region.c | 19 +++++--------------
> >   1 file changed, 5 insertions(+), 14 deletions(-)
> > 
> > diff --git a/drivers/fpga/dfl-afu-dma-region.c b/drivers/fpga/dfl-afu-dma-region.c
> > index 62f924489db5..a31dd3a7e581 100644
> > --- a/drivers/fpga/dfl-afu-dma-region.c
> > +++ b/drivers/fpga/dfl-afu-dma-region.c
> > @@ -16,15 +16,6 @@
> >   #include "dfl-afu.h"
> > -static void put_all_pages(struct page **pages, int npages)
> > -{
> > -	int i;
> > -
> > -	for (i = 0; i < npages; i++)
> > -		if (pages[i])
> > -			put_page(pages[i]);
> > -}
> > -
> >   void afu_dma_region_init(struct dfl_feature_platform_data *pdata)
> >   {
> >   	struct dfl_afu *afu = dfl_fpga_pdata_get_private(pdata);
> > @@ -57,11 +48,11 @@ static int afu_dma_pin_pages(struct dfl_feature_platform_data *pdata,
> >   		goto unlock_vm;
> >   	}
> > -	pinned = get_user_pages_fast(region->user_addr, npages, FOLL_WRITE,
> > +	pinned = pin_user_pages_fast(region->user_addr, npages, FOLL_WRITE,
> >   				     region->pages);
> >   	if (pinned < 0) {
> >   		ret = pinned;
> > -		goto put_pages;
> > +		goto unpin_pages;
> >   	} else if (pinned != npages) {
> >   		ret = -EFAULT;
> >   		goto free_pages;
> > @@ -71,8 +62,8 @@ static int afu_dma_pin_pages(struct dfl_feature_platform_data *pdata,
> >   	return 0;
> > -put_pages:
> > -	put_all_pages(region->pages, pinned);
> > +unpin_pages:
> > +	unpin_user_pages(region->pages, pinned);
> >   free_pages:
> >   	kfree(region->pages);
> >   unlock_vm:
> > @@ -94,7 +85,7 @@ static void afu_dma_unpin_pages(struct dfl_feature_platform_data *pdata,
> >   	long npages = region->length >> PAGE_SHIFT;
> >   	struct device *dev = &pdata->dev->dev;
> > -	put_all_pages(region->pages, npages);
> > +	unpin_user_pages(region->pages, npages);
> >   	kfree(region->pages);
> >   	account_locked_vm(current->mm, npages, false);
> > 
>