linux-kernel - Re: [PATCH 2/2] KVM: x86/mmu: Pass parameter flush as false in kvm_tdp_mmu_zap_collapsible

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Date:   Wed, 17 Nov 2021 09:50:46 -0800
From:   Ben Gardon <bgardon@...gle.com>
To:     Hou Wenlong <houwenlong93@...ux.alibaba.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] KVM: x86/mmu: Pass parameter flush as false in kvm_tdp_mmu_zap_collapsible_sptes()

On Wed, Nov 17, 2021 at 1:20 AM Hou Wenlong
<houwenlong93@...ux.alibaba.com> wrote:
>
> Since tlb flush has been done for legacy MMU before
> kvm_tdp_mmu_zap_collapsible_sptes(), so the parameter flush
> should be false for kvm_tdp_mmu_zap_collapsible_sptes().
>
> Fixes: e2209710ccc5d ("KVM: x86/mmu: Skip rmap operations if rmaps not allocated")
> Signed-off-by: Hou Wenlong <houwenlong93@...ux.alibaba.com>

Haha, I'm glad we're thinking along similar lines. I just sent a patch
yesterday to remove the flush parameter from that function entirely:
https://lore.kernel.org/lkml/20211115234603.2908381-2-bgardon@google.com/
I'll CC you on that patch.

> ---
>  arch/x86/kvm/mmu/mmu.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index d57319e596a9..4b2be04e9862 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -5853,7 +5853,7 @@ static bool kvm_mmu_zap_collapsible_spte(struct kvm *kvm,
>  void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm,
>                                    const struct kvm_memory_slot *slot)
>  {
> -       bool flush = false;
> +       bool flush;
>
>         if (kvm_memslots_have_rmaps(kvm)) {
>                 write_lock(&kvm->mmu_lock);
> @@ -5870,7 +5870,7 @@ void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm,
>
>         if (is_tdp_mmu_enabled(kvm)) {
>                 read_lock(&kvm->mmu_lock);
> -               flush = kvm_tdp_mmu_zap_collapsible_sptes(kvm, slot, flush);
> +               flush = kvm_tdp_mmu_zap_collapsible_sptes(kvm, slot, false);
>                 if (flush)
>                         kvm_arch_flush_remote_tlbs_memslot(kvm, slot);
>                 read_unlock(&kvm->mmu_lock);
> --
> 2.31.1
>