From: Krish Sadhukhan <krish.sadhukhan@oracle.com>
To: Sean Christopherson <sean.j.christopherson@intel.com>,
Paolo Bonzini <pbonzini@redhat.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Xiaoyao Li <xiaoyao.li@intel.com>
Subject: Re: [PATCH] KVM: nVMX: Consult only the "basic" exit reason when routing nested exit
Date: Thu, 27 Feb 2020 12:08:55 -0800 [thread overview]
Message-ID: <ee8c5eb6-9e3d-620b-d51f-bf0534a05d43@oracle.com> (raw)
In-Reply-To: <20200227174430.26371-1-sean.j.christopherson@intel.com>
On 2/27/20 9:44 AM, Sean Christopherson wrote:
> Consult only the basic exit reason, i.e. bits 15:0 of vmcs.EXIT_REASON,
> when determining whether a nested VM-Exit should be reflected into L1 or
> handled by KVM in L0.
>
> For better or worse, the switch statement in nested_vmx_exit_reflected()
> currently defaults to "true", i.e. reflects any nested VM-Exit without
> dedicated logic. Because the case statements only contain the basic
> exit reason, any VM-Exit with modifier bits set will be reflected to L1,
> even if KVM intended to handle it in L0.
>
> Practically speaking, this only affects EXIT_REASON_MCE_DURING_VMENTRY,
> i.e. a #MC that occurs on nested VM-Enter would be incorrectly routed to
> L1, as "failed VM-Entry" is the only modifier that KVM can currently
> encounter. The SMM modifiers will never be generated as KVM doesn't
> support/employ a SMI Transfer Monitor. Ditto for "exit from enclave",
> as KVM doesn't yet support virtualizing SGX, i.e. it's impossible to
> enter an enclave in a KVM guest (L1 or L2).
It seems nested_vmx_exit_reflected() deals only with the basic exit
reason. If it doesn't need anything beyond bits 15:0, may be
vmx_handle_exit() can pass just the base exit reason ?
>
> Fixes: 644d711aa0e1 ("KVM: nVMX: Deciding if L0 or L1 should handle an L2 exit")
> Cc: Jim Mattson <jmattson@google.com>
> Cc: Xiaoyao Li <xiaoyao.li@intel.com>
> Cc: stable@vger.kernel.org
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
> arch/x86/kvm/vmx/nested.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 0946122a8d3b..127065bbde2c 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -5554,7 +5554,7 @@ bool nested_vmx_exit_reflected(struct kvm_vcpu *vcpu, u32 exit_reason)
> vmcs_read32(VM_EXIT_INTR_ERROR_CODE),
> KVM_ISA_VMX);
>
> - switch (exit_reason) {
> + switch ((u16)exit_reason) {
> case EXIT_REASON_EXCEPTION_NMI:
> if (is_nmi(intr_info))
> return false;
Reviewed-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
next prev parent reply other threads:[~2020-02-27 20:10 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-27 17:44 [PATCH] KVM: nVMX: Consult only the "basic" exit reason when routing nested exit Sean Christopherson
2020-02-27 19:20 ` Oliver Upton
2020-02-27 20:08 ` Krish Sadhukhan [this message]
2020-02-27 20:51 ` Sean Christopherson
2020-02-28 9:57 ` Paolo Bonzini
2020-02-28 1:50 linmiaohe
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