From: Christoph Hellwig <hch@lst.de>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: amd-gfx@lists.freedesktop.org, nouveau@lists.freedesktop.org,
dri-devel@lists.freedesktop.org, kvm-ppc@vger.kernel.org,
"Christoph Hellwig" <hch@lst.de>,
linux-mm@kvack.org, "Jerome Glisse" <jglisse@redhat.com>,
"Ben Skeggs" <bskeggs@redhat.com>,
"Dan Williams" <dan.j.williams@intel.com>,
"Bharata B Rao" <bharata@linux.ibm.com>,
"Christian König" <christian.koenig@amd.com>
Subject: Re: [PATCH 4/4] mm: check the device private page owner in hmm_range_fault
Date: Sat, 21 Mar 2020 09:22:36 +0100 [thread overview]
Message-ID: <20200321082236.GB28613@lst.de> (raw)
In-Reply-To: <20200320134109.GA30230@ziepe.ca>
On Fri, Mar 20, 2020 at 10:41:09AM -0300, Jason Gunthorpe wrote:
> Thinking about this some more, does the locking work out here?
>
> hmm_range_fault() runs with mmap_sem in read, and does not lock any of
> the page table levels.
>
> So it relies on accessing stale pte data being safe, and here we
> introduce for the first time a page pointer dereference and a pgmap
> dereference without any locking/refcounting.
>
> The get_dev_pagemap() worked on the PFN and obtained a refcount, so it
> created safety.
>
> Is there some tricky reason this is safe, eg a DEVICE_PRIVATE page
> cannot be removed from the vma without holding mmap_sem in write or
> something?
I don't think there is any specific protection. Let me see if we
can throw in a get_dev_pagemap here - note that current mainline doesn't
even use it for this path..
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next prev parent reply other threads:[~2020-03-21 10:45 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-16 19:32 ensure device private pages have an owner v2 Christoph Hellwig
2020-03-16 19:32 ` [PATCH 1/4] memremap: add an owner field to struct dev_pagemap Christoph Hellwig
2020-03-16 20:55 ` Ralph Campbell
2020-03-16 19:32 ` [PATCH 2/4] mm: handle multiple owners of device private pages in migrate_vma Christoph Hellwig
2020-03-16 21:43 ` Ralph Campbell
2020-03-16 19:32 ` [PATCH 3/4] mm: simplify device private page handling in hmm_range_fault Christoph Hellwig
2020-03-16 19:59 ` Jason Gunthorpe
2020-03-16 21:33 ` Christoph Hellwig
2020-03-16 22:49 ` Ralph Campbell
2020-03-17 7:34 ` Christoph Hellwig
2020-03-17 22:43 ` Ralph Campbell
2020-03-18 9:34 ` Christoph Hellwig
2020-03-17 12:15 ` Jason Gunthorpe
2020-03-17 12:24 ` Christoph Hellwig
2020-03-17 12:28 ` Christoph Hellwig
2020-03-17 12:47 ` Jason Gunthorpe
2020-03-17 12:59 ` Christoph Hellwig
2020-03-17 17:32 ` Jason Gunthorpe
2020-03-17 23:14 ` Ralph Campbell
2020-03-19 18:17 ` Jason Gunthorpe
2020-03-19 22:56 ` Ralph Campbell
2020-03-20 0:03 ` Jason Gunthorpe
2020-03-21 8:20 ` Christoph Hellwig
2020-03-20 0:14 ` Jason Gunthorpe
2020-03-20 1:33 ` Ralph Campbell
2020-03-20 12:58 ` Jason Gunthorpe
2020-03-16 19:32 ` [PATCH 4/4] mm: check the device private page owner " Christoph Hellwig
2020-03-16 19:49 ` Jason Gunthorpe
2020-03-16 23:11 ` Ralph Campbell
2020-03-20 13:41 ` Jason Gunthorpe
2020-03-21 8:22 ` Christoph Hellwig [this message]
2020-03-21 12:38 ` Jason Gunthorpe
2020-03-21 15:18 ` Christoph Hellwig
2020-03-17 5:31 ` ensure device private pages have an owner v2 Bharata B Rao
2020-03-19 0:28 ` Jason Gunthorpe
2020-03-19 7:16 ` Christoph Hellwig
2020-03-19 11:50 ` Jason Gunthorpe
2020-03-19 18:50 ` Jason Gunthorpe
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