linux-kernel - Re: [PATCH] KVM: nVMX: fix comments of handle

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Message-ID: <87lf474ci8.fsf@vitty.brq.redhat.com>
Date:   Wed, 08 Sep 2021 11:55:59 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Yu Zhang <yu.c.zhang@...ux.intel.com>, seanjc@...gle.com,
        pbonzini@...hat.com
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        wanpengli@...cent.com, jmattson@...gle.com, joro@...tes.org
Subject: Re: [PATCH] KVM: nVMX: fix comments of handle_vmon()

Yu Zhang <yu.c.zhang@...ux.intel.com> writes:

> "VMXON pointer" is saved in vmx->nested.vmxon_ptr since
> commit 3573e22cfeca ("KVM: nVMX: additional checks on
> vmxon region"). Also, handle_vmptrld() & handle_vmclear()
> now have logic to check the VMCS pointer against the VMXON
> pointer.
>
> So just remove the obsolete comments of handle_vmon().
>
> Signed-off-by: Yu Zhang <yu.c.zhang@...ux.intel.com>
> ---
>  arch/x86/kvm/vmx/nested.c | 9 +--------
>  1 file changed, 1 insertion(+), 8 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index bc6327950657..90f34f12f883 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -4862,14 +4862,7 @@ static int enter_vmx_operation(struct kvm_vcpu *vcpu)
>  	return -ENOMEM;
>  }
>  
> -/*
> - * Emulate the VMXON instruction.
> - * Currently, we just remember that VMX is active, and do not save or even
> - * inspect the argument to VMXON (the so-called "VMXON pointer") because we
> - * do not currently need to store anything in that guest-allocated memory
> - * region. Consequently, VMCLEAR and VMPTRLD also do not verify that the their
> - * argument is different from the VMXON pointer (which the spec says they do).
> - */
> +/* Emulate the VMXON instruction. */
>  static int handle_vmon(struct kvm_vcpu *vcpu)
>  {
>  	int ret;

Indeed,

Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>

On a slightly related note: we don't seem to reset
'vmx->nested.vmxon_ptr' upon VMXOFF emulation; this is not a problem per
se as we never access it when !vmx->nested.vmxon but I'd still suggest
we do something like

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index bc6327950657..8beb41d02d21 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -290,6 +290,7 @@ static void free_nested(struct kvm_vcpu *vcpu)
 
        vmx->nested.vmxon = false;
        vmx->nested.smm.vmxon = false;
+       vmx->nested.vmxon_ptr = -1ull;
        free_vpid(vmx->nested.vpid02);
        vmx->nested.posted_intr_nv = -1;
        vmx->nested.current_vmptr = -1ull;
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index d7c5257eb5c0..2214e6bd4713 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6884,6 +6884,7 @@ static int vmx_create_vcpu(struct kvm_vcpu *vcpu)
 
        vcpu_setup_sgx_lepubkeyhash(vcpu);
 
+       vmx->nested.vmxon_ptr = -1ull;
        vmx->nested.posted_intr_nv = -1;
        vmx->nested.current_vmptr = -1ull;
        vmx->nested.hv_evmcs_vmptr = EVMPTR_INVALID;

to avoid issues in the future.

-- 
Vitaly