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Subject: Re: [PATCH V4 7/15] KVM/MMU: Flush tlb directly in the
 kvm_zap_gfn_range()
To:     lantianyu1986@gmail.com
Cc:     Lan Tianyu <Tianyu.Lan@microsoft.com>, kys@microsoft.com,
        haiyangz@microsoft.com, sthemmin@microsoft.com, tglx@linutronix.de,
        mingo@redhat.com, hpa@zytor.com, x86@kernel.org,
        rkrcmar@redhat.com, devel@linuxdriverproject.org,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        michael.h.kelley@microsoft.com, vkuznets@redhat.com
References: <20181013145406.4911-1-Tianyu.Lan@microsoft.com>
 <20181013145406.4911-8-Tianyu.Lan@microsoft.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
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Message-ID: <bdb05a65-f849-7346-61b7-99c444050254@redhat.com>
Date:   Mon, 15 Oct 2018 12:04:29 +0200
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Sender: linux-kernel-owner@vger.kernel.org
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On 13/10/2018 16:53, lantianyu1986@gmail.com wrote:
> +	bool flush = false;
>  	int i;
>  
>  	spin_lock(&kvm->mmu_lock);
> @@ -5654,18 +5655,27 @@ void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end)
>  		slots = __kvm_memslots(kvm, i);
>  		kvm_for_each_memslot(memslot, slots) {
>  			gfn_t start, end;
> +			bool flush_tlb = true;
>  
>  			start = max(gfn_start, memslot->base_gfn);
>  			end = min(gfn_end, memslot->base_gfn + memslot->npages);
>  			if (start >= end)
>  				continue;
>  
> -			slot_handle_level_range(kvm, memslot, kvm_zap_rmapp,
> -						PT_PAGE_TABLE_LEVEL, PT_MAX_HUGEPAGE_LEVEL,
> -						start, end - 1, true);
> +			if (kvm_available_flush_tlb_with_range())
> +				flush_tlb = false;

This should be moved outside the for, because it's invariant.

> +			flush = slot_handle_level_range(kvm, memslot,
> +					kvm_zap_rmapp, PT_PAGE_TABLE_LEVEL,
> +					PT_MAX_HUGEPAGE_LEVEL, start,
> +					end - 1, flush_tlb);

... and this should be "flush |= ".
>  		}
>  	}
>  
> +	if (flush && kvm_available_flush_tlb_with_range())
> +		kvm_flush_remote_tlbs_with_address(kvm, gfn_start,
> +				gfn_end - gfn_start + 1);
> +

... and this can be just if (flush), because if flush_tlb is true then
slot_handle_level_range always returns false.

Paolo