[PATCH MANUALSEL 5.4 1/2] KVM: nVMX: eVMCS: Filter out VM_EXIT_SAVE_VMX_PREEMPTION_TIMER

[PATCH MANUALSEL 5.4 1/2] KVM: nVMX: eVMCS: Filter out VM_EXIT_SAVE_VMX_PREEMPTION_TIMER

[Sasha Levin]

From: Vitaly Kuznetsov <vkuznets@redhat.com>

[ Upstream commit 7a601e2cf61558dfd534a9ecaad09f5853ad8204 ]

Enlightened VMCS v1 doesn't have VMX_PREEMPTION_TIMER_VALUE field,
PIN_BASED_VMX_PREEMPTION_TIMER is also filtered out already so it makes
sense to filter out VM_EXIT_SAVE_VMX_PREEMPTION_TIMER too.

Note, none of the currently existing Windows/Hyper-V versions are known
to enable 'save VMX-preemption timer value' when eVMCS is in use, the
change is aimed at making the filtering future proof.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20220112170134.1904308-3-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/x86/kvm/vmx/evmcs.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/evmcs.h b/arch/x86/kvm/vmx/evmcs.h
index 07ebf6882a458..632bed227152e 100644
--- a/arch/x86/kvm/vmx/evmcs.h
+++ b/arch/x86/kvm/vmx/evmcs.h
@@ -58,7 +58,9 @@ DECLARE_STATIC_KEY_FALSE(enable_evmcs);
 	 SECONDARY_EXEC_SHADOW_VMCS |					\
 	 SECONDARY_EXEC_TSC_SCALING |					\
 	 SECONDARY_EXEC_PAUSE_LOOP_EXITING)
-#define EVMCS1_UNSUPPORTED_VMEXIT_CTRL (VM_EXIT_LOAD_IA32_PERF_GLOBAL_CTRL)
+#define EVMCS1_UNSUPPORTED_VMEXIT_CTRL					\
+	(VM_EXIT_LOAD_IA32_PERF_GLOBAL_CTRL |				\
+	 VM_EXIT_SAVE_VMX_PREEMPTION_TIMER)
 #define EVMCS1_UNSUPPORTED_VMENTRY_CTRL (VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL)
 #define EVMCS1_UNSUPPORTED_VMFUNC (VMX_VMFUNC_EPTP_SWITCHING)
 
-- 
2.34.1

[PATCH MANUALSEL 5.4 2/2] KVM: nVMX: WARN on any attempt to allocate shadow VMCS for vmcs02

[Sasha Levin]

From: Sean Christopherson <seanjc@google.com>

[ Upstream commit d6e656cd266cdcc95abd372c7faef05bee271d1a ]

WARN if KVM attempts to allocate a shadow VMCS for vmcs02.  KVM emulates
VMCS shadowing but doesn't virtualize it, i.e. KVM should never allocate
a "real" shadow VMCS for L2.

The previous code WARNed but continued anyway with the allocation,
presumably in an attempt to avoid NULL pointer dereference.
However, alloc_vmcs (and hence alloc_shadow_vmcs) can fail, and
indeed the sole caller does:

	if (enable_shadow_vmcs && !alloc_shadow_vmcs(vcpu))
		goto out_shadow_vmcs;

which makes it not a useful attempt.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220125220527.2093146-1-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 arch/x86/kvm/vmx/nested.c | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 3041015b05f71..44e11f6db3efe 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -4360,18 +4360,20 @@ static struct vmcs *alloc_shadow_vmcs(struct kvm_vcpu *vcpu)
 	struct loaded_vmcs *loaded_vmcs = vmx->loaded_vmcs;
 
 	/*
-	 * We should allocate a shadow vmcs for vmcs01 only when L1
-	 * executes VMXON and free it when L1 executes VMXOFF.
-	 * As it is invalid to execute VMXON twice, we shouldn't reach
-	 * here when vmcs01 already have an allocated shadow vmcs.
+	 * KVM allocates a shadow VMCS only when L1 executes VMXON and frees it
+	 * when L1 executes VMXOFF or the vCPU is forced out of nested
+	 * operation.  VMXON faults if the CPU is already post-VMXON, so it
+	 * should be impossible to already have an allocated shadow VMCS.  KVM
+	 * doesn't support virtualization of VMCS shadowing, so vmcs01 should
+	 * always be the loaded VMCS.
 	 */
-	WARN_ON(loaded_vmcs == &vmx->vmcs01 && loaded_vmcs->shadow_vmcs);
+	if (WARN_ON(loaded_vmcs != &vmx->vmcs01 || loaded_vmcs->shadow_vmcs))
+		return loaded_vmcs->shadow_vmcs;
+
+	loaded_vmcs->shadow_vmcs = alloc_vmcs(true);
+	if (loaded_vmcs->shadow_vmcs)
+		vmcs_clear(loaded_vmcs->shadow_vmcs);
 
-	if (!loaded_vmcs->shadow_vmcs) {
-		loaded_vmcs->shadow_vmcs = alloc_vmcs(true);
-		if (loaded_vmcs->shadow_vmcs)
-			vmcs_clear(loaded_vmcs->shadow_vmcs);
-	}
 	return loaded_vmcs->shadow_vmcs;
 }
 
-- 
2.34.1

Re: [PATCH MANUALSEL 5.4 2/2] KVM: nVMX: WARN on any attempt to allocate shadow VMCS for vmcs02

[Paolo Bonzini]

On 2/9/22 19:57, Sasha Levin wrote:
> From: Sean Christopherson <seanjc@google.com>
> 
> [ Upstream commit d6e656cd266cdcc95abd372c7faef05bee271d1a ]
> 
> WARN if KVM attempts to allocate a shadow VMCS for vmcs02.  KVM emulates
> VMCS shadowing but doesn't virtualize it, i.e. KVM should never allocate
> a "real" shadow VMCS for L2.
> 
> The previous code WARNed but continued anyway with the allocation,
> presumably in an attempt to avoid NULL pointer dereference.
> However, alloc_vmcs (and hence alloc_shadow_vmcs) can fail, and
> indeed the sole caller does:
> 
> 	if (enable_shadow_vmcs && !alloc_shadow_vmcs(vcpu))
> 		goto out_shadow_vmcs;
> 
> which makes it not a useful attempt.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> Message-Id: <20220125220527.2093146-1-seanjc@google.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
>   arch/x86/kvm/vmx/nested.c | 22 ++++++++++++----------
>   1 file changed, 12 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 3041015b05f71..44e11f6db3efe 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -4360,18 +4360,20 @@ static struct vmcs *alloc_shadow_vmcs(struct kvm_vcpu *vcpu)
>   	struct loaded_vmcs *loaded_vmcs = vmx->loaded_vmcs;
>   
>   	/*
> -	 * We should allocate a shadow vmcs for vmcs01 only when L1
> -	 * executes VMXON and free it when L1 executes VMXOFF.
> -	 * As it is invalid to execute VMXON twice, we shouldn't reach
> -	 * here when vmcs01 already have an allocated shadow vmcs.
> +	 * KVM allocates a shadow VMCS only when L1 executes VMXON and frees it
> +	 * when L1 executes VMXOFF or the vCPU is forced out of nested
> +	 * operation.  VMXON faults if the CPU is already post-VMXON, so it
> +	 * should be impossible to already have an allocated shadow VMCS.  KVM
> +	 * doesn't support virtualization of VMCS shadowing, so vmcs01 should
> +	 * always be the loaded VMCS.
>   	 */
> -	WARN_ON(loaded_vmcs == &vmx->vmcs01 && loaded_vmcs->shadow_vmcs);
> +	if (WARN_ON(loaded_vmcs != &vmx->vmcs01 || loaded_vmcs->shadow_vmcs))
> +		return loaded_vmcs->shadow_vmcs;
> +
> +	loaded_vmcs->shadow_vmcs = alloc_vmcs(true);
> +	if (loaded_vmcs->shadow_vmcs)
> +		vmcs_clear(loaded_vmcs->shadow_vmcs);
>   
> -	if (!loaded_vmcs->shadow_vmcs) {
> -		loaded_vmcs->shadow_vmcs = alloc_vmcs(true);
> -		if (loaded_vmcs->shadow_vmcs)
> -			vmcs_clear(loaded_vmcs->shadow_vmcs);
> -	}
>   	return loaded_vmcs->shadow_vmcs;
>   }
>   

NACK

Re: [PATCH MANUALSEL 5.4 1/2] KVM: nVMX: eVMCS: Filter out VM_EXIT_SAVE_VMX_PREEMPTION_TIMER

[Paolo Bonzini]

On 2/9/22 19:57, Sasha Levin wrote:
> From: Vitaly Kuznetsov <vkuznets@redhat.com>
> 
> [ Upstream commit 7a601e2cf61558dfd534a9ecaad09f5853ad8204 ]

Acked-by: Paolo Bonzini <pbonzini@redhat.com>

Paolo

> Enlightened VMCS v1 doesn't have VMX_PREEMPTION_TIMER_VALUE field,
> PIN_BASED_VMX_PREEMPTION_TIMER is also filtered out already so it makes
> sense to filter out VM_EXIT_SAVE_VMX_PREEMPTION_TIMER too.
> 
> Note, none of the currently existing Windows/Hyper-V versions are known
> to enable 'save VMX-preemption timer value' when eVMCS is in use, the
> change is aimed at making the filtering future proof.
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> Message-Id: <20220112170134.1904308-3-vkuznets@redhat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
>   arch/x86/kvm/vmx/evmcs.h | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/vmx/evmcs.h b/arch/x86/kvm/vmx/evmcs.h
> index 07ebf6882a458..632bed227152e 100644
> --- a/arch/x86/kvm/vmx/evmcs.h
> +++ b/arch/x86/kvm/vmx/evmcs.h
> @@ -58,7 +58,9 @@ DECLARE_STATIC_KEY_FALSE(enable_evmcs);
>   	 SECONDARY_EXEC_SHADOW_VMCS |					\
>   	 SECONDARY_EXEC_TSC_SCALING |					\
>   	 SECONDARY_EXEC_PAUSE_LOOP_EXITING)
> -#define EVMCS1_UNSUPPORTED_VMEXIT_CTRL (VM_EXIT_LOAD_IA32_PERF_GLOBAL_CTRL)
> +#define EVMCS1_UNSUPPORTED_VMEXIT_CTRL					\
> +	(VM_EXIT_LOAD_IA32_PERF_GLOBAL_CTRL |				\
> +	 VM_EXIT_SAVE_VMX_PREEMPTION_TIMER)
>   #define EVMCS1_UNSUPPORTED_VMENTRY_CTRL (VM_ENTRY_LOAD_IA32_PERF_GLOBAL_CTRL)
>   #define EVMCS1_UNSUPPORTED_VMFUNC (VMX_VMFUNC_EPTP_SWITCHING)
>