[PATCH] KVM: x86: allow KVM_REQ_GET_NESTED_STATE_PAGES outside guest mode for VMX

[PATCH] KVM: x86: allow KVM_REQ_GET_NESTED_STATE_PAGES outside guest mode for VMX

[Paolo Bonzini]

VMX also uses KVM_REQ_GET_NESTED_STATE_PAGES for the Hyper-V eVMCS,
which may need to be loaded outside guest mode.  Therefore we cannot
WARN in that case.

However, that part of nested_get_vmcs12_pages is _not_ needed at
vmentry time.  Split it out of KVM_REQ_GET_NESTED_STATE_PAGES handling,
so that both vmentry and migration (and in the latter case, independent
of is_guest_mode) do the parts that are needed.

Cc: <stable@vger.kernel.org> # 5.10.x: f2c7ef3ba: KVM: nSVM: cancel KVM_REQ_GET_NESTED_STATE_PAGES
Cc: <stable@vger.kernel.org> # 5.10.x
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 arch/x86/kvm/svm/nested.c |  3 +++
 arch/x86/kvm/vmx/nested.c | 32 ++++++++++++++++++++++++++------
 arch/x86/kvm/x86.c        |  4 +---
 3 files changed, 30 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index cb4c6ee10029..7a605ad8254d 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -200,6 +200,9 @@ static bool svm_get_nested_state_pages(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
 
+	if (WARN_ON(!is_guest_mode(vcpu)))
+		return true;
+
 	if (!nested_svm_vmrun_msrpm(svm)) {
 		vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
 		vcpu->run->internal.suberror =
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 0fbb46990dfc..20ab40a2ac34 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -3124,13 +3124,9 @@ static int nested_vmx_check_vmentry_hw(struct kvm_vcpu *vcpu)
 	return 0;
 }
 
-static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
+static bool nested_get_evmcs_page(struct kvm_vcpu *vcpu)
 {
-	struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
-	struct kvm_host_map *map;
-	struct page *page;
-	u64 hpa;
 
 	/*
 	 * hv_evmcs may end up being not mapped after migration (when
@@ -3152,6 +3148,19 @@ static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
 			return false;
 		}
 	}
+	return true;
+}
+
+static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
+{
+	struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
+	struct vcpu_vmx *vmx = to_vmx(vcpu);
+	struct kvm_host_map *map;
+	struct page *page;
+	u64 hpa;
+
+	if (!nested_get_evmcs_page(vcpu))
+		return false;
 
 	if (nested_cpu_has2(vmcs12, SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES)) {
 		/*
@@ -3224,6 +3233,17 @@ static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
 	return true;
 }
 
+static bool vmx_get_nested_state_pages(struct kvm_vcpu *vcpu)
+{
+	if (!nested_get_evmcs_page(vcpu))
+		return false;
+
+	if (is_guest_mode(vcpu) && !nested_get_vmcs12_pages(vcpu))
+		return false;
+
+	return true;
+}
+
 static int nested_vmx_write_pml_buffer(struct kvm_vcpu *vcpu, gpa_t gpa)
 {
 	struct vmcs12 *vmcs12;
@@ -6602,7 +6622,7 @@ struct kvm_x86_nested_ops vmx_nested_ops = {
 	.hv_timer_pending = nested_vmx_preemption_timer_pending,
 	.get_state = vmx_get_nested_state,
 	.set_state = vmx_set_nested_state,
-	.get_nested_state_pages = nested_get_vmcs12_pages,
+	.get_nested_state_pages = vmx_get_nested_state_pages,
 	.write_log_dirty = nested_vmx_write_pml_buffer,
 	.enable_evmcs = nested_enable_evmcs,
 	.get_evmcs_version = nested_get_evmcs_version,
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 9a8969a6dd06..b910aa74ee05 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -8802,9 +8802,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 
 	if (kvm_request_pending(vcpu)) {
 		if (kvm_check_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu)) {
-			if (WARN_ON_ONCE(!is_guest_mode(vcpu)))
-				;
-			else if (unlikely(!kvm_x86_ops.nested_ops->get_nested_state_pages(vcpu))) {
+			if (unlikely(!kvm_x86_ops.nested_ops->get_nested_state_pages(vcpu))) {
 				r = 0;
 				goto out;
 			}
-- 
2.26.2

Re: [PATCH] KVM: x86: allow KVM_REQ_GET_NESTED_STATE_PAGES outside guest mode for VMX

[Sean Christopherson]

On Mon, Jan 25, 2021, Paolo Bonzini wrote:
> +static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
> +{
> +	struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
> +	struct vcpu_vmx *vmx = to_vmx(vcpu);
> +	struct kvm_host_map *map;
> +	struct page *page;
> +	u64 hpa;
> +
> +	if (!nested_get_evmcs_page(vcpu))
> +		return false;
>  
>  	if (nested_cpu_has2(vmcs12, SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES)) {
>  		/*
> @@ -3224,6 +3233,17 @@ static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
>  	return true;
>  }
>  
> +static bool vmx_get_nested_state_pages(struct kvm_vcpu *vcpu)
> +{
> +	if (!nested_get_evmcs_page(vcpu))
> +		return false;
> +
> +	if (is_guest_mode(vcpu) && !nested_get_vmcs12_pages(vcpu))
> +		return false;

nested_get_evmcs_page() will get called twice in the common case of
is_guest_mode() == true.  I can't tell if that will ever be fatal, but it's
definitely weird.  Maybe this?

	if (!is_guest_mode(vcpu))
		return nested_get_evmcs_page(vcpu);

	return nested_get_vmcs12_pages(vcpu);

> +
> +	return true;
> +}
> +
>  static int nested_vmx_write_pml_buffer(struct kvm_vcpu *vcpu, gpa_t gpa)
>  {
>  	struct vmcs12 *vmcs12;
> @@ -6602,7 +6622,7 @@ struct kvm_x86_nested_ops vmx_nested_ops = {
>  	.hv_timer_pending = nested_vmx_preemption_timer_pending,
>  	.get_state = vmx_get_nested_state,
>  	.set_state = vmx_set_nested_state,
> -	.get_nested_state_pages = nested_get_vmcs12_pages,
> +	.get_nested_state_pages = vmx_get_nested_state_pages,
>  	.write_log_dirty = nested_vmx_write_pml_buffer,
>  	.enable_evmcs = nested_enable_evmcs,
>  	.get_evmcs_version = nested_get_evmcs_version,
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 9a8969a6dd06..b910aa74ee05 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -8802,9 +8802,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>  
>  	if (kvm_request_pending(vcpu)) {
>  		if (kvm_check_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu)) {
> -			if (WARN_ON_ONCE(!is_guest_mode(vcpu)))
> -				;
> -			else if (unlikely(!kvm_x86_ops.nested_ops->get_nested_state_pages(vcpu))) {
> +			if (unlikely(!kvm_x86_ops.nested_ops->get_nested_state_pages(vcpu))) {
>  				r = 0;
>  				goto out;
>  			}
> -- 
> 2.26.2
> 

Re: [PATCH] KVM: x86: allow KVM_REQ_GET_NESTED_STATE_PAGES outside guest mode for VMX

[Paolo Bonzini]

On 25/01/21 20:16, Sean Christopherson wrote:
>>   }
>>   
>> +static bool vmx_get_nested_state_pages(struct kvm_vcpu *vcpu)
>> +{
>> +	if (!nested_get_evmcs_page(vcpu))
>> +		return false;
>> +
>> +	if (is_guest_mode(vcpu) && !nested_get_vmcs12_pages(vcpu))
>> +		return false;
> nested_get_evmcs_page() will get called twice in the common case of
> is_guest_mode() == true.  I can't tell if that will ever be fatal, but it's
> definitely weird.  Maybe this?
> 
> 	if (!is_guest_mode(vcpu))
> 		return nested_get_evmcs_page(vcpu);
> 
> 	return nested_get_vmcs12_pages(vcpu);
> 

I wouldn't say there is a common case; however the idea was to remove 
the call to nested_get_evmcs_page from nested_get_vmcs12_pages, since 
that one is only needed after KVM_GET_NESTED_STATE and not during 
VMLAUNCH/VMRESUME.

Paolo

Re: [PATCH] KVM: x86: allow KVM_REQ_GET_NESTED_STATE_PAGES outside guest mode for VMX

[Sean Christopherson]

On Mon, Jan 25, 2021, Paolo Bonzini wrote:
> On 25/01/21 20:16, Sean Christopherson wrote:
> > >   }
> > > +static bool vmx_get_nested_state_pages(struct kvm_vcpu *vcpu)
> > > +{
> > > +	if (!nested_get_evmcs_page(vcpu))
> > > +		return false;
> > > +
> > > +	if (is_guest_mode(vcpu) && !nested_get_vmcs12_pages(vcpu))
> > > +		return false;
> > nested_get_evmcs_page() will get called twice in the common case of
> > is_guest_mode() == true.  I can't tell if that will ever be fatal, but it's
> > definitely weird.  Maybe this?
> > 
> > 	if (!is_guest_mode(vcpu))
> > 		return nested_get_evmcs_page(vcpu);
> > 
> > 	return nested_get_vmcs12_pages(vcpu);
> > 
> 
> I wouldn't say there is a common case;

Eh, I would argue that it is more common to do KVM_REQ_GET_NESTED_STATE_PAGES
with is_guest_mode() than it is with !is_guest_mode(), as the latter is valid if
and only if eVMCS is in use.  But, I think we're only vying for internet points. :-)

> however the idea was to remove the call to nested_get_evmcs_page from
> nested_get_vmcs12_pages, since that one is only needed after
> KVM_GET_NESTED_STATE and not during VMLAUNCH/VMRESUME.

I'm confused, this patch explicitly adds a call to nested_get_evmcs_page() in
nested_get_vmcs12_pages().

Re: [PATCH] KVM: x86: allow KVM_REQ_GET_NESTED_STATE_PAGES outside guest mode for VMX

[Paolo Bonzini]

On 25/01/21 20:53, Sean Christopherson wrote:
> Eh, I would argue that it is more common to do KVM_REQ_GET_NESTED_STATE_PAGES
> with is_guest_mode() than it is with !is_guest_mode(), as the latter is valid if
> and only if eVMCS is in use.  But, I think we're only vying for internet points.:-)
> 
>> however the idea was to remove the call to nested_get_evmcs_page from
>> nested_get_vmcs12_pages, since that one is only needed after
>> KVM_GET_NESTED_STATE and not during VMLAUNCH/VMRESUME.
>
> I'm confused, this patch explicitly adds a call to nested_get_evmcs_page() in
> nested_get_vmcs12_pages().

What I really meant is that the patch was wrong. :/

I'll send my pull request to Linus without this one, and include it 
later this week.

Paolo