linux-kernel - Re: [PATCH V3 4/13] KVM/MMU: Flush tlb directly in the kvm_handle_hva

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Date:   Mon, 1 Oct 2018 17:03:57 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Tianyu Lan <Tianyu.Lan@...rosoft.com>
Cc:     KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Michael Kelley (EOSG)" <Michael.H.Kelley@...rosoft.com>,
        vkuznets <vkuznets@...hat.com>,
        Jork Loeser <Jork.Loeser@...rosoft.com>
Subject: Re: [PATCH V3 4/13] KVM/MMU: Flush tlb directly in the
 kvm_handle_hva_range()

On 27/09/2018 05:49, Tianyu Lan wrote:
> This patch is to flush tlb directly in the kvm_handle_hva_range()
> when range flush is available.
> 
> Signed-off-by: Lan Tianyu <Tianyu.Lan@...rosoft.com>
> ---
>  arch/x86/kvm/mmu.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index d10d8423e8d6..877edae0401f 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -1888,6 +1888,13 @@ static int kvm_handle_hva_range(struct kvm *kvm,
>  						 &iterator)
>  				ret |= handler(kvm, iterator.rmap, memslot,
>  					       iterator.gfn, iterator.level, data);
> +
> +			if (ret && kvm_available_flush_tlb_with_range()) {
> +				kvm_flush_remote_tlbs_with_address(kvm,
> +						gfn_start,
> +						gfn_end - gfn_start);
> +				ret = 0;
> +			}
>  		}
>  	}
>  
> 


Not all callers need a TLB flush (in particular kvm_test_age_hva)
require a flush.  My suggestion is to rewrite kvm_test_age_hva like this:

index 4705a7f4169e..f72364a0ef9c 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -1898,12 +1898,13 @@ static int kvm_test_age_rmapp(struct kvm *kvm,
 			      struct kvm_memory_slot *slot, gfn_t gfn,
 			      int level, unsigned long data)
 {
+	bool *result = (bool *)data;
 	u64 *sptep;
 	struct rmap_iterator iter;

 	for_each_rmap_spte(rmap_head, &iter, sptep)
 		if (is_accessed_spte(*sptep))
-			return 1;
+			*result = true;
 	return 0;
 }

@@ -1929,7 +1930,10 @@ int kvm_age_hva(struct kvm *kvm,

 int kvm_test_age_hva(struct kvm *kvm, unsigned long hva)
 {
-	return kvm_handle_hva(kvm, hva, 0, kvm_test_age_rmapp);
+	bool result = false;
+	kvm_handle_hva(kvm, hva, (unsigned long) &result,
+		        kvm_test_age_rmapp);
+	return result;
 }

 #ifdef MMU_DEBUG

and move the flush from kvm_set_pte_rmapp to
kvm_mmu_notifier_change_pte, making kvm_set_spte_hva return an int;
otherwise, it will flush twice.  For non-x86 architectures just grep for
"set_spte_hva" and make the various kvm_set_spte_hva implementations
return false.

Paolo