linux-kernel - Re: [RFC 01/19] KVM: x86/mmu: Fix TLB flush range when handling disconnected pt

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Date:   Thu, 11 Nov 2021 17:44:45 +0000
From:   David Matlack <dmatlack@...gle.com>
To:     Ben Gardon <bgardon@...gle.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Peter Xu <peterx@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Peter Shier <pshier@...gle.com>,
        Mingwei Zhang <mizhang@...gle.com>,
        Yulei Zhang <yulei.kernel@...il.com>,
        Wanpeng Li <kernellwp@...il.com>,
        Xiao Guangrong <xiaoguangrong.eric@...il.com>,
        Kai Huang <kai.huang@...el.com>,
        Keqian Zhu <zhukeqian1@...wei.com>,
        David Hildenbrand <david@...hat.com>, stable@...r.kernel.org
Subject: Re: [RFC 01/19] KVM: x86/mmu: Fix TLB flush range when handling
 disconnected pt

On Wed, Nov 10, 2021 at 02:29:52PM -0800, Ben Gardon wrote:
> When recursively clearing out disconnected pts, the range based TLB
> flush in handle_removed_tdp_mmu_page uses the wrong starting GFN,
> resulting in the flush mostly missing the affected range. Fix this by
> using base_gfn for the flush.
> 
> Fixes: a066e61f13cf ("KVM: x86/mmu: Factor out handling of removed page tables")
> CC: stable@...r.kernel.org
> 
> Signed-off-by: Ben Gardon <bgardon@...gle.com>
> ---
>  arch/x86/kvm/mmu/tdp_mmu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index 7c5dd83e52de..866c2b191e1e 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -374,7 +374,7 @@ static void handle_removed_tdp_mmu_page(struct kvm *kvm, tdp_ptep_t pt,
>  				    shared);
>  	}
>  
> -	kvm_flush_remote_tlbs_with_address(kvm, gfn,
> +	kvm_flush_remote_tlbs_with_address(kvm, base_gfn,

Suggest pulling the definition of gfn into the for loop as well (along
with sptep and old_child_spte for that matter) so that referencing it
here isn't even possible.

>  					   KVM_PAGES_PER_HPAGE(level + 1));
>  
>  	call_rcu(&sp->rcu_head, tdp_mmu_free_sp_rcu_callback);
> -- 
> 2.34.0.rc0.344.g81b53c2807-goog
>