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From: Jan Kara <jack@suse.cz>
To: John Hubbard <jhubbard@nvidia.com>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
	"Al Viro" <viro@zeniv.linux.org.uk>,
	"Alex Williamson" <alex.williamson@redhat.com>,
	"Benjamin Herrenschmidt" <benh@kernel.crashing.org>,
	"Björn Töpel" <bjorn.topel@intel.com>,
	"Christoph Hellwig" <hch@infradead.org>,
	"Dan Williams" <dan.j.williams@intel.com>,
	"Daniel Vetter" <daniel@ffwll.ch>,
	"Dave Chinner" <david@fromorbit.com>,
	"David Airlie" <airlied@linux.ie>,
	"David S . Miller" <davem@davemloft.net>,
	"Ira Weiny" <ira.weiny@intel.com>, "Jan Kara" <jack@suse.cz>,
	"Jason Gunthorpe" <jgg@ziepe.ca>, "Jens Axboe" <axboe@kernel.dk>,
	"Jonathan Corbet" <corbet@lwn.net>,
	"Jérôme Glisse" <jglisse@redhat.com>,
	"Magnus Karlsson" <magnus.karlsson@intel.com>,
	"Mauro Carvalho Chehab" <mchehab@kernel.org>,
	"Michael Ellerman" <mpe@ellerman.id.au>,
	"Michal Hocko" <mhocko@suse.com>,
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Subject: Re: [PATCH 17/19] powerpc: book3s64: convert to pin_user_pages() and put_user_page()
Date: Mon, 25 Nov 2019 09:59:15 +0100
Message-ID: <20191125085915.GB1797@quack2.suse.cz> (raw)
In-Reply-To: <20191125042011.3002372-18-jhubbard@nvidia.com>

On Sun 24-11-19 20:20:09, 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(). In this case, do so via put_user_pages_dirty_lock().
> 
> That has the side effect of calling set_page_dirty_lock(), instead
> of set_page_dirty(). This is probably more accurate.
> 
> As Christoph Hellwig put it, "set_page_dirty() is only safe if we are
> dealing with a file backed page where we have reference on the inode it
> hangs off." [1]
> 
> 3. Release each page in mem->hpages[] (instead of mem->hpas[]), because
> that is the array that pin_longterm_pages() filled in. This is more
> accurate and should be a little safer from a maintenance point of
> view.

Except that this breaks the code. hpages is unioned with hpas...

> [1] https://lore.kernel.org/r/20190723153640.GB720@lst.de
> 
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> ---
>  arch/powerpc/mm/book3s64/iommu_api.c | 12 +++++-------
>  1 file changed, 5 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/powerpc/mm/book3s64/iommu_api.c b/arch/powerpc/mm/book3s64/iommu_api.c
> index 56cc84520577..196383e8e5a9 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);
> @@ -212,10 +211,9 @@ static void mm_iommu_unpin(struct mm_iommu_table_group_mem_t *mem)
>  		if (!page)
>  			continue;
>  
> -		if (mem->hpas[i] & MM_IOMMU_TABLE_GROUP_PAGE_DIRTY)
> -			SetPageDirty(page);
> +		put_user_pages_dirty_lock(&mem->hpages[i], 1,
> +					  MM_IOMMU_TABLE_GROUP_PAGE_DIRTY);

And the dirtying condition is wrong here as well. Currently it is always
true.

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

  reply index

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-25  4:19 [PATCH 00/19] pin_user_pages(): reduced-risk series for Linux 5.5 John Hubbard
2019-11-25  4:19 ` [PATCH 01/19] mm/gup: factor out duplicate code from four routines John Hubbard
2019-11-25  4:19 ` [PATCH 02/19] mm/gup: move try_get_compound_head() to top, fix minor issues John Hubbard
2019-11-25  4:19 ` [PATCH 03/19] mm: Cleanup __put_devmap_managed_page() vs ->page_free() John Hubbard
2019-11-25  4:19 ` [PATCH 04/19] goldish_pipe: rename local pin_user_pages() routine John Hubbard
2019-11-25  4:19 ` [PATCH 05/19] mm: fix get_user_pages_remote()'s handling of FOLL_LONGTERM John Hubbard
2019-11-25  4:19 ` [PATCH 06/19] vfio: fix FOLL_LONGTERM use, simplify get_user_pages_remote() call John Hubbard
2019-11-25  4:19 ` [PATCH 07/19] mm/gup: introduce pin_user_pages*() and FOLL_PIN John Hubbard
2019-11-25  7:47   ` kbuild test robot
2019-11-25  8:44   ` kbuild test robot
2019-11-25 20:13     ` John Hubbard
2019-11-25  4:20 ` [PATCH 08/19] goldish_pipe: convert to pin_user_pages() and put_user_page() John Hubbard
2019-11-25  4:20 ` [PATCH 09/19] IB/{core,hw,umem}: set FOLL_PIN via pin_user_pages*(), fix up ODP John Hubbard
2019-11-25  4:20 ` [PATCH 10/19] mm/process_vm_access: set FOLL_PIN via pin_user_pages_remote() John Hubbard
2019-11-25  4:20 ` [PATCH 11/19] drm/via: set FOLL_PIN via pin_user_pages_fast() John Hubbard
2019-11-25  4:20 ` [PATCH 12/19] fs/io_uring: set FOLL_PIN via pin_user_pages() John Hubbard
2019-11-25  4:20 ` [PATCH 13/19] net/xdp: " John Hubbard
2019-11-25  4:20 ` [PATCH 14/19] media/v4l2-core: set pages dirty upon releasing DMA buffers John Hubbard
2019-11-25  4:20 ` [PATCH 15/19] media/v4l2-core: pin_user_pages (FOLL_PIN) and put_user_page() conversion John Hubbard
2019-11-25  4:20 ` [PATCH 16/19] vfio, mm: " John Hubbard
2019-11-25  4:20 ` [PATCH 17/19] powerpc: book3s64: convert to pin_user_pages() and put_user_page() John Hubbard
2019-11-25  8:59   ` Jan Kara [this message]
2019-11-25 20:46     ` John Hubbard
2019-11-25  4:20 ` [PATCH 18/19] mm/gup_benchmark: use proper FOLL_WRITE flags instead of hard-coding "1" John Hubbard
2019-11-25  4:20 ` [PATCH 19/19] mm, tree-wide: rename put_user_page*() to unpin_user_page*() John Hubbard

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