From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrea Arcangeli <andrea@qumranet.com>
Subject: [ofa-general] Re: [PATCH 0 of 9] mmu notifier #v12
Date: Tue, 22 Apr 2008 14:00:56 +0200
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Cc: Nick Piggin <npiggin@suse.de>, Jack Steiner <steiner@sgi.com>,
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On Tue, Apr 22, 2008 at 09:20:26AM +0200, Andrea Arcangeli wrote:
>     invalidate_range_start {
> 	spin_lock(&kvm->mmu_lock);
> 
> 	kvm->invalidate_range_count++;
> 	rmap-invalidate of sptes in range
> 

	write_seqlock; write_sequnlock;

> 	spin_unlock(&kvm->mmu_lock)
>     }
> 
>     invalidate_range_end {
> 	spin_lock(&kvm->mmu_lock);
> 
> 	kvm->invalidate_range_count--;


	write_seqlock; write_sequnlock;

> 
> 	spin_unlock(&kvm->mmu_lock)
>     }

Robin correctly pointed out by PM there should be a seqlock in
range_begin/end too like corrected above.

I guess it's better to use an explicit sequence counter so we avoid an
useless spinlock of the write_seqlock (mmu_lock is enough already in
all places) and so we can increase it with a single op with +=2 in the
range_begin/end. The above is a lower-perf version of the final
locking but simpler for reading purposes.