linux-kernel - Re: [PATCH v3 02/15] KVM: MMU: lazily drop large spte

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Date:	Tue, 12 Nov 2013 20:44:59 -0200
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
Cc:	gleb@...hat.com, avi.kivity@...il.com, pbonzini@...hat.com,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v3 02/15] KVM: MMU: lazily drop large spte

On Wed, Oct 23, 2013 at 09:29:20PM +0800, Xiao Guangrong wrote:
> Currently, kvm zaps the large spte if write-protected is needed, the later
> read can fault on that spte. Actually, we can make the large spte readonly
> instead of making them un-present, the page fault caused by read access can
> be avoided
> 
> The idea is from Avi:
> | As I mentioned before, write-protecting a large spte is a good idea,
> | since it moves some work from protect-time to fault-time, so it reduces
> | jitter.  This removes the need for the return value.
> 
> This version has fixed the issue reported in 6b73a9606, the reason of that
> issue is that fast_page_fault() directly sets the readonly large spte to
> writable but only dirty the first page into the dirty-bitmap that means
> other pages are missed. Fixed it by only the normal sptes (on the
> PT_PAGE_TABLE_LEVEL level) can be fast fixed
> 
> Signed-off-by: Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>

Reviewed-by: Marcelo Tosatti <mtosatti@...hat.com>

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