linux-kernel - Re: [PATCH 1/1] KVM: x86/mmu: Set memory encryption "value", not "mask", in shadow PDPTRs

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Date:   Wed, 8 Jun 2022 14:37:27 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Yuan Yao <yuan.yao@...el.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Kai Huang <kai.huang@...el.com>,
        Yuan Yao <yuan.yao@...ux.intel.com>
Subject: Re: [PATCH 1/1] KVM: x86/mmu: Set memory encryption "value", not
 "mask", in shadow PDPTRs

On 6/8/22 03:20, Yuan Yao wrote:
> Assign shadow_me_value, not shadow_me_mask, to PAE root entries,
> a.k.a. shadow PDPTRs, when host memory encryption is supported.  The
> "mask" is the set of all possible memory encryption bits, e.g. MKTME
> KeyIDs, whereas "value" holds the actual value that needs to be
> stuffed into host page tables.
> 
> Using shadow_me_mask results in a failed VM-Entry due to setting
> reserved PA bits in the PDPTRs, and ultimately causes an OOPS due to
> physical addresses with non-zero MKTME bits sending to_shadow_page()
> into the weeds:
> 
> set kvm_intel.dump_invalid_vmcs=1 to dump internal KVM state.
> BUG: unable to handle page fault for address: ffd43f00063049e8
> PGD 86dfd8067 P4D 0
> Oops: 0000 [#1] PREEMPT SMP
> RIP: 0010:mmu_free_root_page+0x3c/0x90 [kvm]
>   kvm_mmu_free_roots+0xd1/0x200 [kvm]
>   __kvm_mmu_unload+0x29/0x70 [kvm]
>   kvm_mmu_unload+0x13/0x20 [kvm]
>   kvm_arch_destroy_vm+0x8a/0x190 [kvm]
>   kvm_put_kvm+0x197/0x2d0 [kvm]
>   kvm_vm_release+0x21/0x30 [kvm]
>   __fput+0x8e/0x260
>   ____fput+0xe/0x10
>   task_work_run+0x6f/0xb0
>   do_exit+0x327/0xa90
>   do_group_exit+0x35/0xa0
>   get_signal+0x911/0x930
>   arch_do_signal_or_restart+0x37/0x720
>   exit_to_user_mode_prepare+0xb2/0x140
>   syscall_exit_to_user_mode+0x16/0x30
>   do_syscall_64+0x4e/0x90
>   entry_SYSCALL_64_after_hwframe+0x44/0xae
> 
> Fixes: e54f1ff244ac ("KVM: x86/mmu: Add shadow_me_value and repurpose shadow_me_mask")
> Signed-off-by: Yuan Yao <yuan.yao@...el.com>
> Reviewed-by: Kai Huang <kai.huang@...el.com>
> ---
>   arch/x86/kvm/mmu/mmu.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index efe5a3dca1e0..6bd144f1e60c 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -3411,7 +3411,7 @@ static int mmu_alloc_direct_roots(struct kvm_vcpu *vcpu)
>   			root = mmu_alloc_root(vcpu, i << (30 - PAGE_SHIFT),
>   					      i << 30, PT32_ROOT_LEVEL, true);
>   			mmu->pae_root[i] = root | PT_PRESENT_MASK |
> -					   shadow_me_mask;
> +					   shadow_me_value;
>   		}
>   		mmu->root.hpa = __pa(mmu->pae_root);
>   	} else {

Queued, thanks.

Paolo