linux-kernel - Re: [patch -mm 1/2] i386: add ptep_test_and_clear

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Message-ID: <Pine.LNX.4.64.0703260721490.18961@blonde.wat.veritas.com>
Date:	Mon, 26 Mar 2007 07:27:07 +0100 (BST)
From:	Hugh Dickins <hugh@...itas.com>
To:	Zachary Amsden <zach@...are.com>
cc:	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [patch -mm 1/2] i386: add ptep_test_and_clear_{dirty,young}

On Sun, 25 Mar 2007, Zachary Amsden wrote:
> 
> If you actually clear the bit, you need to:
> 
> +         pte_update_defer(vma->vm_mm, addr, ptep);
> 
> The reason is, when updating PTEs, the hypervisor must be notified.  Using
> atomic operations to do this is fine for all hypervisors I am aware of.
> However, for hypervisors which shadow page tables, if these PTE modifications
> are not trapped, you need a post-modification call to fulfill the update of
> the shadow page table.

Thanks for the very rapid response.

So, David just needs to move the pte_update_defer out of
ptep_clear_flush_* and into ptep_test_and_clear_*?

That leaves me wondering why you deleted ptep_test_and_clear_*
(while leaving their __HAVE_ARCHes) in the first place?

Hugh
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