linux-kernel - Re: ptrace and pfn mappings

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Message-Id: <1160484135.6177.15.camel@localhost.localdomain>
Date:	Tue, 10 Oct 2006 22:42:15 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Nick Piggin <nickpiggin@...oo.com.au>,
	Nick Piggin <npiggin@...e.de>, Hugh Dickins <hugh@...itas.com>,
	Linux Memory Management <linux-mm@...ck.org>,
	Andrew Morton <akpm@...l.org>, Jes Sorensen <jes@....com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: ptrace and pfn mappings


> 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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