linux-kernel - Re: [PATCH v3 1/6] KVM: x86/mmu: Fix wrong gfn range of tlb flushing in validate_direct

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Date:   Wed, 28 Sep 2022 20:51:33 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Hou Wenlong <houwenlong.hwl@...group.com>
Cc:     kvm@...r.kernel.org, David Matlack <dmatlack@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Lan Tianyu <Tianyu.Lan@...rosoft.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/6] KVM: x86/mmu: Fix wrong gfn range of tlb flushing
 in validate_direct_spte()

On Fri, Sep 23, 2022, 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.

Please wrap closer to ~75 chars.

> Fixes: c3134ce240eed ("KVM: Replace old tlb flush function with new one to flush a specified range.")
> Suggested-by: David Matlack <dmatlack@...gle.com>
> Signed-off-by: Hou Wenlong <houwenlong.hwl@...group.com>
> ---
>  arch/x86/kvm/mmu/mmu.c          |  9 ++++++++-
>  arch/x86/kvm/mmu/mmu_internal.h | 10 ++++++++++
>  2 files changed, 18 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index e418ef3ecfcb..ae9f84b0fc64 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -260,6 +260,13 @@ 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_gfn(kvm, sp->gfn, sp->role.level + 1);
> +}
> +
>  static void mark_mmio_spte(struct kvm_vcpu *vcpu, u64 *sptep, u64 gfn,
>  			   unsigned int access)
>  {
> @@ -2341,7 +2348,7 @@ 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);

As mentioned very belatedly[*], I would rather move this patch later in the series
and use kvm_flush_remote_tlbs_sptep() instead of introducing a one-off helper.

[*] https://lore.kernel.org/all/YzMoWghqNJdYBlaE@google.com