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

From: David Matlack <dmatlack@google.com>
To: Ben Gardon <bgardon@google.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
	Paolo Bonzini <pbonzini@redhat.com>, Peter Xu <peterx@redhat.com>,
	Sean Christopherson <seanjc@google.com>,
	Peter Shier <pshier@google.com>,
	Mingwei Zhang <mizhang@google.com>,
	Yulei Zhang <yulei.kernel@gmail.com>,
	Wanpeng Li <kernellwp@gmail.com>,
	Xiao Guangrong <xiaoguangrong.eric@gmail.com>,
	Kai Huang <kai.huang@intel.com>,
	Keqian Zhu <zhukeqian1@huawei.com>,
	David Hildenbrand <david@redhat.com>,
	stable@vger.kernel.org
Subject: Re: [RFC 01/19] KVM: x86/mmu: Fix TLB flush range when handling disconnected pt
Date: Thu, 11 Nov 2021 17:44:45 +0000	[thread overview]
Message-ID: <YY1Wje9zNEch6XvG@google.com> (raw)
In-Reply-To: <20211110223010.1392399-2-bgardon@google.com>

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@vger.kernel.org
> 
> Signed-off-by: Ben Gardon <bgardon@google.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
> 