linux-kernel - Re: [PATCH v2 4/5] KVM: MMU: introduce page_fault_start and page_fault

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Date:	Tue, 18 Sep 2012 20:43:07 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
Cc:	Avi Kivity <avi@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
	KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v2 4/5] KVM: MMU: introduce page_fault_start and
 page_fault_end

On Tue, Sep 18, 2012 at 04:15:32PM +0800, Xiao Guangrong wrote:
> On 09/15/2012 11:25 PM, Marcelo Tosatti wrote:
> > On Fri, Sep 14, 2012 at 05:59:06PM +0800, Xiao Guangrong wrote:
> >> Wrap the common operations into these two functions
> >>
> >> Signed-off-by: Xiao Guangrong <xiaoguangrong@...ux.vnet.ibm.com>
> > 
> > Why? I think people are used to 
> > 
> > spin_lock(lock)
> > sequence
> > spin_unlock(lock)
> 
> Marcelo,
> 
> There are many functions use this style that wrap the lock into the
> _start and _end functions in kernel (eg.: cgroup_pidlist_start and
> cgroup_pidlist_stop in kernel/cgroup.c).
> 
> Actually, i just wanted to remove below duplicate ugly code:
> 
> 	if (!is_error_pfn(pfn))
> 		kvm_release_pfn_clean(pfn);
> 
> > 
> > So its easy to verify whether access to data structures are protected.
> > 
> > Unrelated to this patch, one opportunity i see to simplify this
> > code is:
> > 
> > - error pfn / mmio pfn / invalid pfn relation
> > 
> > Have the meaning of this bits unified in a single function/helper, see
> > comment to patch 1 (perhaps you can further improve).
> 
> Sorry, more detail?

Should force the reader of the code to understand error pfn / mmio pfn /
invalid pfn in a single helper. That is, avoid using error pfn at all.

> 
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