linux-kernel - Re: [PATCH] kvm: mmu: fix is_tdp_mmu_check when the TDP MMU is not in use

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Date:   Mon, 16 Nov 2020 09:19:41 -0800
From:   Ben Gardon <bgardon@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>
Subject: Re: [PATCH] kvm: mmu: fix is_tdp_mmu_check when the TDP MMU is not in use

On Sun, Nov 15, 2020 at 7:27 AM Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> In some cases where shadow paging is in use, the root page will
> be either mmu->pae_root or vcpu->arch.mmu->lm_root.  Then it will
> not have an associated struct kvm_mmu_page, because it is allocated
> with alloc_page instead of kvm_mmu_alloc_page.
>
> Just return false quickly from is_tdp_mmu_root if the TDP MMU is
> not in use, which also includes the case where shadow paging is
> enabled.
>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>

Reviewed-by: Ben Gardon <bgardon@...gle.com>

> ---
>  arch/x86/kvm/mmu/tdp_mmu.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index 27e381c9da6c..ff28a5c6abd6 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -49,7 +49,14 @@ bool is_tdp_mmu_root(struct kvm *kvm, hpa_t hpa)
>  {
>         struct kvm_mmu_page *sp;
>
> +       if (!kvm->arch.tdp_mmu_enabled)
> +               return false;
> +       if (WARN_ON(!VALID_PAGE(hpa)))
> +               return false;
> +
>         sp = to_shadow_page(hpa);
> +       if (WARN_ON(!sp))
> +               return false;
>
>         return sp->tdp_mmu_page && sp->root_count;
>  }
> --
> 2.26.2
>