linux-kernel - Re: [PATCH] KVM: x86: take as_id into account when checking PGD

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Message-ID: <88e517df-0887-2687-b3db-0892ac479211@redhat.com>
Date:   Wed, 8 Jul 2020 16:06:09 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: x86: take as_id into account when checking PGD

On 08/07/20 16:00, Vitaly Kuznetsov wrote:
> OVMF booted guest running on shadow pages crashes on TRIPLE FAULT after
> enabling paging from SMM. The crash is triggered from mmu_check_root() and
> is caused by kvm_is_visible_gfn() searching through memslots with as_id = 0
> while vCPU may be in a different context (address space).
> 
> Introduce kvm_vcpu_is_visible_gfn() and use it from mmu_check_root().
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
>  arch/x86/kvm/mmu/mmu.c   | 2 +-
>  include/linux/kvm_host.h | 1 +
>  virt/kvm/kvm_main.c      | 8 ++++++++
>  3 files changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 4fd4b5de8996..309024210a35 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -3668,7 +3668,7 @@ static int mmu_check_root(struct kvm_vcpu *vcpu, gfn_t root_gfn)
>  {
>  	int ret = 0;
>  
> -	if (!kvm_is_visible_gfn(vcpu->kvm, root_gfn)) {
> +	if (!kvm_vcpu_is_visible_gfn(vcpu, root_gfn)) {
>  		kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
>  		ret = 1;
>  	}
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index d564855243d8..f74d2a5afc26 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -774,6 +774,7 @@ int kvm_clear_guest_page(struct kvm *kvm, gfn_t gfn, int offset, int len);
>  int kvm_clear_guest(struct kvm *kvm, gpa_t gpa, unsigned long len);
>  struct kvm_memory_slot *gfn_to_memslot(struct kvm *kvm, gfn_t gfn);
>  bool kvm_is_visible_gfn(struct kvm *kvm, gfn_t gfn);
> +bool kvm_vcpu_is_visible_gfn(struct kvm_vcpu *vcpu, gfn_t gfn);
>  unsigned long kvm_host_page_size(struct kvm_vcpu *vcpu, gfn_t gfn);
>  void mark_page_dirty(struct kvm *kvm, gfn_t gfn);
>  
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index a852af5c3214..b131c7da1d12 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1626,6 +1626,14 @@ bool kvm_is_visible_gfn(struct kvm *kvm, gfn_t gfn)
>  }
>  EXPORT_SYMBOL_GPL(kvm_is_visible_gfn);
>  
> +bool kvm_vcpu_is_visible_gfn(struct kvm_vcpu *vcpu, gfn_t gfn)
> +{
> +	struct kvm_memory_slot *memslot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);
> +
> +	return kvm_is_visible_memslot(memslot);
> +}
> +EXPORT_SYMBOL_GPL(kvm_vcpu_is_visible_gfn);
> +
>  unsigned long kvm_host_page_size(struct kvm_vcpu *vcpu, gfn_t gfn)
>  {
>  	struct vm_area_struct *vma;
> 

Queued, thanks.

Paolo