netdev - Re: [PATCH v9 20/25] powerpc: book3s64: convert to pin_user_pages() and put_user

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Date:   Wed, 11 Dec 2019 11:42:36 +0100
From:   Jan Kara <jack@...e.cz>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Alex Williamson <alex.williamson@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Björn Töpel <bjorn.topel@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Dave Chinner <david@...morbit.com>,
        David Airlie <airlied@...ux.ie>,
        "David S . Miller" <davem@...emloft.net>,
        Ira Weiny <ira.weiny@...el.com>, Jan Kara <jack@...e.cz>,
        Jason Gunthorpe <jgg@...pe.ca>, Jens Axboe <axboe@...nel.dk>,
        Jonathan Corbet <corbet@....net>,
        Jérôme Glisse <jglisse@...hat.com>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Michal Hocko <mhocko@...e.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Paul Mackerras <paulus@...ba.org>,
        Shuah Khan <shuah@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>, bpf@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, kvm@...r.kernel.org,
        linux-block@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-media@...r.kernel.org, linux-rdma@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, netdev@...r.kernel.org,
        linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v9 20/25] powerpc: book3s64: convert to pin_user_pages()
 and put_user_page()

On Tue 10-12-19 18:53:13, John Hubbard wrote:
> 1. Convert from get_user_pages() to pin_user_pages().
> 
> 2. As required by pin_user_pages(), release these pages via
> put_user_page().
> 
> Cc: Jan Kara <jack@...e.cz>
> Signed-off-by: John Hubbard <jhubbard@...dia.com>

The patch looks good to me. You can add:

Reviewed-by: Jan Kara <jack@...e.cz>

I'd just note that mm_iommu_do_alloc() has a pre-existing bug that the last
jump to 'free_exit' (at line 157) happens already after converting page
pointers to physical addresses so put_page() calls there will just crash.
But that's completely unrelated to your change. I'll send a fix separately.

								Honza

> ---
>  arch/powerpc/mm/book3s64/iommu_api.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/powerpc/mm/book3s64/iommu_api.c b/arch/powerpc/mm/book3s64/iommu_api.c
> index 56cc84520577..a86547822034 100644
> --- a/arch/powerpc/mm/book3s64/iommu_api.c
> +++ b/arch/powerpc/mm/book3s64/iommu_api.c
> @@ -103,7 +103,7 @@ static long mm_iommu_do_alloc(struct mm_struct *mm, unsigned long ua,
>  	for (entry = 0; entry < entries; entry += chunk) {
>  		unsigned long n = min(entries - entry, chunk);
>  
> -		ret = get_user_pages(ua + (entry << PAGE_SHIFT), n,
> +		ret = pin_user_pages(ua + (entry << PAGE_SHIFT), n,
>  				FOLL_WRITE | FOLL_LONGTERM,
>  				mem->hpages + entry, NULL);
>  		if (ret == n) {
> @@ -167,9 +167,8 @@ static long mm_iommu_do_alloc(struct mm_struct *mm, unsigned long ua,
>  	return 0;
>  
>  free_exit:
> -	/* free the reference taken */
> -	for (i = 0; i < pinned; i++)
> -		put_page(mem->hpages[i]);
> +	/* free the references taken */
> +	put_user_pages(mem->hpages, pinned);
>  
>  	vfree(mem->hpas);
>  	kfree(mem);
> @@ -215,7 +214,8 @@ static void mm_iommu_unpin(struct mm_iommu_table_group_mem_t *mem)
>  		if (mem->hpas[i] & MM_IOMMU_TABLE_GROUP_PAGE_DIRTY)
>  			SetPageDirty(page);
>  
> -		put_page(page);
> +		put_user_page(page);
> +
>  		mem->hpas[i] = 0;
>  	}
>  }
> -- 
> 2.24.0
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR