Re: [kvm-devel] [PATCH 0 of 9] mmu notifier #v12

[Andrea A. <an...@qu...>]

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.