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Date:   Wed, 7 Sep 2022 10:43:54 -0700
From:   David Matlack <dmatlack@google.com>
To:     Hou Wenlong <houwenlong.hwl@antgroup.com>
Cc:     kvm@vger.kernel.org, Sean Christopherson <seanjc@google.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>,
        Lan Tianyu <Tianyu.Lan@microsoft.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 1/6] KVM: x86/mmu: Fix wrong gfn range of tlb flushing
 in validate_direct_spte()
Message-ID: <YxjYWtgLZMxFBrjl@google.com>
References: <cover.1661331396.git.houwenlong.hwl@antgroup.com>
 <c0ee12e44f2d218a0857a5e05628d05462b32bf9.1661331396.git.houwenlong.hwl@antgroup.com>
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On Wed, Aug 24, 2022 at 05:29:18PM +0800, Hou Wenlong wrote:
> The spte pointing to the children SP is dropped, so the
> whole gfn range covered by the children SP should be flushed.
> Although, Hyper-V may treat a 1-page flush the same if the
> address points to a huge page, it still would be better
> to use the correct size of huge page. Also introduce
> a helper function to do range-based flushing when a direct
> SP is dropped, which would help prevent future buggy use
> of kvm_flush_remote_tlbs_with_address() in such case.
> 
> Fixes: c3134ce240eed ("KVM: Replace old tlb flush function with new one to flush a specified range.")
> Suggested-by: David Matlack <dmatlack@google.com>
> Signed-off-by: Hou Wenlong <houwenlong.hwl@antgroup.com>
> ---
>  arch/x86/kvm/mmu/mmu.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index e418ef3ecfcb..a3578abd8bbc 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -260,6 +260,14 @@ void kvm_flush_remote_tlbs_with_address(struct kvm *kvm,
>  	kvm_flush_remote_tlbs_with_range(kvm, &range);
>  }
>  
> +/* Flush all memory mapped by the given direct SP. */
> +static void kvm_flush_remote_tlbs_direct_sp(struct kvm *kvm, struct kvm_mmu_page *sp)
> +{
> +	WARN_ON_ONCE(!sp->role.direct);
> +	kvm_flush_remote_tlbs_with_address(kvm, sp->gfn,
> +					   KVM_PAGES_PER_HPAGE(sp->role.level + 1));

nit: I think it would make sense to introduce
kvm_flush_remote_tlbs_gfn() in this patch since you are going to
eventually use it here anyway.

> +}
> +
>  static void mark_mmio_spte(struct kvm_vcpu *vcpu, u64 *sptep, u64 gfn,
>  			   unsigned int access)
>  {
> @@ -2341,7 +2349,7 @@ static void validate_direct_spte(struct kvm_vcpu *vcpu, u64 *sptep,
>  			return;
>  
>  		drop_parent_pte(child, sptep);
> -		kvm_flush_remote_tlbs_with_address(vcpu->kvm, child->gfn, 1);
> +		kvm_flush_remote_tlbs_direct_sp(vcpu->kvm, child);
>  	}
>  }
>  
> -- 
> 2.31.1
>