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

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Date:   Thu, 9 Jun 2022 06:53:33 +0800
From:   Yuan Yao <yuan.yao@...ux.intel.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Yuan Yao <yuan.yao@...el.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        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>
Subject: Re: [PATCH 1/1] KVM: x86/mmu: Set memory encryption "value", not
 "mask", in shadow PDPTRs

On Wed, Jun 08, 2022 at 02:37:27PM +0200, Paolo Bonzini wrote:
> 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

Thanks Paolo, and Thanks again to Sean Christopherson
<seanjc@...gle.com>'s nice help for patch subject/format on this patch
(was [PATCH 1/1] KVM: MMU: Fix VM entry failure and OOPS for shdaow
page table).

>