From: Maxim Levitsky <mlevitsk@redhat.com>
To: Vitaly Kuznetsov <vkuznets@redhat.com>,
kvm@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 6/7] KVM: nVMX: Request to sync eVMCS from VMCS12 after migration
Date: Mon, 24 May 2021 15:35:30 +0300 [thread overview]
Message-ID: <42df9cffffb3b29630ab9cc37b8b038397ce6d02.camel@redhat.com> (raw)
In-Reply-To: <20210517135054.1914802-7-vkuznets@redhat.com>
On Mon, 2021-05-17 at 15:50 +0200, Vitaly Kuznetsov wrote:
> VMCS12 is used to keep the authoritative state during nested state
> migration. In case 'need_vmcs12_to_shadow_sync' flag is set, we're
> in between L2->L1 vmexit and L1 guest run when actual sync to
> enlightened (or shadow) VMCS happens. Nested state, however, has
> no flag for 'need_vmcs12_to_shadow_sync' so vmx_set_nested_state()->
> set_current_vmptr() always sets it. Enlightened vmptrld path, however,
> doesn't have the quirk so some VMCS12 changes may not get properly
> reflected to eVMCS and L1 will see an incorrect state.
>
> Note, during L2 execution or when need_vmcs12_to_shadow_sync is not
> set the change is effectively a nop: in the former case all changes
> will get reflected during the first L2->L1 vmexit and in the later
> case VMCS12 and eVMCS are already in sync (thanks to
> copy_enlightened_to_vmcs12() in vmx_get_nested_state()).
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
> arch/x86/kvm/vmx/nested.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 3bfbf991bf45..a0dedd413a23 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -3127,6 +3127,12 @@ static bool nested_get_evmcs_page(struct kvm_vcpu *vcpu)
> if (evmptrld_status == EVMPTRLD_VMFAIL ||
> evmptrld_status == EVMPTRLD_ERROR)
> return false;
> +
> + /*
> + * Post migration VMCS12 always provides the most actual
> + * information, copy it to eVMCS upon entry.
> + */
> + vmx->nested.need_vmcs12_to_shadow_sync = true;
I noticed that bug too while reviewing the previous patches,
wasted some time thinking about it :-(
This does look like a clean and correct way to fix this, unless
you adopt my suggestion to sync evmcs right away on nested vmexit
as I explained in my review of patch 3 of this series.
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Best regards,
Maxim Levitsky
> }
>
> return true;
next prev parent reply other threads:[~2021-05-24 12:35 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-17 13:50 [PATCH v2 0/7] KVM: nVMX: Fixes for nested state migration when eVMCS is in use Vitaly Kuznetsov
2021-05-17 13:50 ` [PATCH v2 1/7] KVM: nVMX: Introduce nested_evmcs_is_used() Vitaly Kuznetsov
2021-05-24 12:11 ` Maxim Levitsky
2021-05-24 12:35 ` Vitaly Kuznetsov
2021-05-26 14:34 ` Maxim Levitsky
2021-05-27 7:54 ` Vitaly Kuznetsov
2021-05-27 14:10 ` Maxim Levitsky
2021-05-24 13:54 ` Paolo Bonzini
2021-05-24 14:09 ` Vitaly Kuznetsov
2021-05-24 14:18 ` Paolo Bonzini
2021-05-24 14:37 ` Vitaly Kuznetsov
2021-05-17 13:50 ` [PATCH v2 2/7] KVM: nVMX: Release enlightened VMCS on VMCLEAR Vitaly Kuznetsov
2021-05-24 12:13 ` Maxim Levitsky
2021-05-17 13:50 ` [PATCH v2 3/7] KVM: nVMX: Ignore 'hv_clean_fields' data when eVMCS data is copied in vmx_get_nested_state() Vitaly Kuznetsov
2021-05-24 12:26 ` Maxim Levitsky
2021-05-24 13:01 ` Vitaly Kuznetsov
2021-05-24 13:58 ` Paolo Bonzini
2021-05-26 14:44 ` Maxim Levitsky
2021-05-24 13:56 ` Paolo Bonzini
2021-05-24 14:12 ` Vitaly Kuznetsov
2021-05-17 13:50 ` [PATCH v2 4/7] KVM: nVMX: Force enlightened VMCS sync from nested_vmx_failValid() Vitaly Kuznetsov
2021-05-24 12:27 ` Maxim Levitsky
2021-05-17 13:50 ` [PATCH v2 5/7] KVM: nVMX: Reset eVMCS clean fields data from prepare_vmcs02() Vitaly Kuznetsov
2021-05-24 12:34 ` Maxim Levitsky
2021-05-24 13:07 ` Vitaly Kuznetsov
2021-05-17 13:50 ` [PATCH v2 6/7] KVM: nVMX: Request to sync eVMCS from VMCS12 after migration Vitaly Kuznetsov
2021-05-24 12:35 ` Maxim Levitsky [this message]
2021-05-17 13:50 ` [PATCH v2 7/7] KVM: selftests: evmcs_test: Test that KVM_STATE_NESTED_EVMCS is never lost Vitaly Kuznetsov
2021-05-24 12:36 ` Maxim Levitsky
2021-05-24 12:08 ` [PATCH v2 0/7] KVM: nVMX: Fixes for nested state migration when eVMCS is in use Maxim Levitsky
2021-05-24 12:44 ` Vitaly Kuznetsov
2021-05-26 14:41 ` Maxim Levitsky
2021-05-27 8:01 ` Vitaly Kuznetsov
2021-05-27 14:11 ` Maxim Levitsky
2021-05-27 14:17 ` Paolo Bonzini
2021-05-24 14:01 ` Paolo Bonzini
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