Subject: Re: ptrace and pfn mappings
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Christoph Hellwig <hch@infradead.org>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>, Nick Piggin <npiggin@suse.de>,
       Hugh Dickins <hugh@veritas.com>,
       Linux Memory Management <linux-mm@kvack.org>,
       Andrew Morton <akpm@osdl.org>, Jes Sorensen <jes@sgi.com>,
       Linux Kernel <linux-kernel@vger.kernel.org>,
       Ingo Molnar <mingo@elte.hu>
In-Reply-To: <20061010123128.GA23775@infradead.org>
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Date: Tue, 10 Oct 2006 22:42:15 +1000
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> I think the best idea is to add a new ->access method to the vm_operations
> that's called by access_process_vm() when it exists and VM_IO or VM_PFNMAP
> are set.   ->access would take the required object locks and copy out the
> data manually.  This should work both for spufs and drm.

Another option is to have access_process_vm() lookup the PTE and lock it
while copying the data from the page.

something like

	- lookup pte & lock
	- check if pte still present
	- copy data to temp kernel buffer
	- unlock pte
	- copy data to user buffer

Ben.

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