linux-kernel - Re: [PATCH 2/9] KVM: MMU: introduce slot_handle

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Date:	Thu, 07 May 2015 14:04:34 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	guangrong.xiao@...ux.intel.com
CC:	gleb@...nel.org, mtosatti@...hat.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/9] KVM: MMU: introduce slot_handle_level() and its helper



On 30/04/2015 12:24, guangrong.xiao@...ux.intel.com wrote:
> From: Xiao Guangrong <guangrong.xiao@...ux.intel.com>
> 
> There are several places walking all rmaps for the memslot so that
> introduce common functions to cleanup the code
> 
> Signed-off-by: Xiao Guangrong <guangrong.xiao@...ux.intel.com>
> ---
>  arch/x86/kvm/mmu.c | 63 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 63 insertions(+)
> 
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index ea3e3e4..75a3459 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -4410,6 +4410,69 @@ void kvm_mmu_setup(struct kvm_vcpu *vcpu)
>  	init_kvm_mmu(vcpu);
>  }
>  
> +/* The return value indicates if tlb flush on all vcpus is needed. */
> +typedef bool (*slot_level_handler) (struct kvm *kvm, unsigned long *rmap);
> +
> +/* The caller should hold mmu-lock before calling this function. */
> +static bool
> +slot_handle_level(struct kvm *kvm, struct kvm_memory_slot *memslot,
> +		  slot_level_handler fn, int min_level, int max_level,
> +		  bool lock_flush_tlb)

Why not introduce for_each_slot_rmap first, instead of introducing one 
implementation first and then switching to another?  It's a small 
change to reorder the patches like that.  I think we should have three 
iterator macros:

#define for_each_rmap_spte(rmap, iter, spte)

#define for_each_slot_rmap(slot, min_level, max_level, iter, rmapp)

#define for_each_slot_rmap_range(slot, iter, min_level, max_level, \
				 start_gfn, end_gfn, iter, rmapp)

where the last two take care of initializing the walker/iterator in the 
first part of the "for".

This way, this function would be introduced immediately as this very 
readable code:

	struct slot_rmap_iterator iter;
	unsigned long *rmapp;
	bool flush = false;

	for_each_slot_rmap(memslot, min_level, max_level, &iter, rmapp) {
		if (*rmapp)
			flush |= fn(kvm, rmapp);

		if (need_resched() || spin_needbreak(&kvm->mmu_lock)) {
			if (flush && lock_flush_tlb) {
				kvm_flush_remote_tlbs(kvm);
				flush = false;
			}
			cond_resched_lock(&kvm->mmu_lock);
		}
	}

	/*
	 * What about adding this here: then callers that pass
	 * lock_flush_tlb == true need not care about the return
	 * value!
	 */
	if (flush && lock_flush_tlb) {
		kvm_flush_remote_tlbs(kvm);
		flush = false;
	}

	return flush;

In addition, some of these functions need to be marked always_inline I 
think; either slot_handle_level/slot_handle_*_level, or the
iterators/walkers.  Can you collect kvm.ko size for both cases?

Thanks,

Paolo

> +{
> +	unsigned long last_gfn;
> +	bool flush = false;
> +	int level;
> +
> +	last_gfn = memslot->base_gfn + memslot->npages - 1;
> +
> +	for (level = min_level; level <= max_level; ++level) {
> +		unsigned long *rmapp;
> +		unsigned long last_index, index;
> +
> +		rmapp = memslot->arch.rmap[level - PT_PAGE_TABLE_LEVEL];
> +		last_index = gfn_to_index(last_gfn, memslot->base_gfn, level);
> +
> +		for (index = 0; index <= last_index; ++index, ++rmapp) {
> +			if (*rmapp)
> +				flush |= fn(kvm, rmapp);
> +
> +			if (need_resched() || spin_needbreak(&kvm->mmu_lock)) {
> +				if (flush && lock_flush_tlb) {
> +					kvm_flush_remote_tlbs(kvm);
> +					flush = false;
> +				}
> +				cond_resched_lock(&kvm->mmu_lock);
> +			}
> +		}
> +	}
> +
> +	return flush;
> +}
> +
> +static bool
> +slot_handle_all_level(struct kvm *kvm, struct kvm_memory_slot *memslot,
> +		      slot_level_handler fn, bool lock_flush_tlb)
> +{
> +	return slot_handle_level(kvm, memslot, fn, PT_PAGE_TABLE_LEVEL,
> +		PT_PAGE_TABLE_LEVEL + KVM_NR_PAGE_SIZES - 1, lock_flush_tlb);
> +}
> +
> +static bool
> +slot_handle_large_level(struct kvm *kvm, struct kvm_memory_slot *memslot,
> +			slot_level_handler fn, bool lock_flush_tlb)
> +{
> +	return slot_handle_level(kvm, memslot, fn, PT_PAGE_TABLE_LEVEL + 1,
> +		PT_PAGE_TABLE_LEVEL + KVM_NR_PAGE_SIZES - 1, lock_flush_tlb);
> +}
> +
> +static bool
> +slot_handle_leaf(struct kvm *kvm, struct kvm_memory_slot *memslot,
> +		 slot_level_handler fn, bool lock_flush_tlb)
> +{
> +	return slot_handle_level(kvm, memslot, fn, PT_PAGE_TABLE_LEVEL,
> +				 PT_PAGE_TABLE_LEVEL, lock_flush_tlb);
> +}
> +
>  void kvm_mmu_slot_remove_write_access(struct kvm *kvm,
>  				      struct kvm_memory_slot *memslot)
>  {
> 
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