[PATCH v4] KVM: nVMX: nested TPR shadow/threshold emulation

[PATCH v4] KVM: nVMX: nested TPR shadow/threshold emulation

[Wanpeng Li]

This patch fix bug https://bugzilla.kernel.org/show_bug.cgi?id=61411

TPR shadow/threshold feature is important to speed up the Windows guest.
Besides, it is a must feature for certain VMM.

We map virtual APIC page address and TPR threshold from L1 VMCS. If
TPR_BELOW_THRESHOLD VM exit is triggered by L2 guest and L1 interested
in, we inject it into L1 VMM for handling.

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com>
---
v3 -> v4:
 * add Paolo's Reviewed-by
 * unconditionally fail the vmentry, with a comment  
 * setup the TPR_SHADOW/virtual_apic_page of vmcs02 based on vmcs01 if L2 owns the APIC
v2 -> v3:
 * nested vm entry failure if both tpr shadow and cr8 exiting bits are not set
v1 -> v2:
 * don't take L0's "virtualize APIC accesses" setting into account
 * virtual_apic_page do exactly the same thing that is done for apic_access_page
 * add the tpr threshold field to the read-write fields for shadow VMCS

 arch/x86/kvm/vmx.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 47 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index bfe11cf..c8d8e9a 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -379,6 +379,7 @@ struct nested_vmx {
 	 * we must keep them pinned while L2 runs.
 	 */
 	struct page *apic_access_page;
+	struct page *virtual_apic_page;
 	u64 msr_ia32_feature_control;
 
 	struct hrtimer preemption_timer;
@@ -533,6 +534,7 @@ static int max_shadow_read_only_fields =
 	ARRAY_SIZE(shadow_read_only_fields);
 
 static unsigned long shadow_read_write_fields[] = {
+	TPR_THRESHOLD,
 	GUEST_RIP,
 	GUEST_RSP,
 	GUEST_CR0,
@@ -2330,7 +2332,7 @@ static __init void nested_vmx_setup_ctls_msrs(void)
 		CPU_BASED_MOV_DR_EXITING | CPU_BASED_UNCOND_IO_EXITING |
 		CPU_BASED_USE_IO_BITMAPS | CPU_BASED_MONITOR_EXITING |
 		CPU_BASED_RDPMC_EXITING | CPU_BASED_RDTSC_EXITING |
-		CPU_BASED_PAUSE_EXITING |
+		CPU_BASED_PAUSE_EXITING | CPU_BASED_TPR_SHADOW |
 		CPU_BASED_ACTIVATE_SECONDARY_CONTROLS;
 	/*
 	 * We can allow some features even when not supported by the
@@ -6148,6 +6150,10 @@ static void free_nested(struct vcpu_vmx *vmx)
 		nested_release_page(vmx->nested.apic_access_page);
 		vmx->nested.apic_access_page = 0;
 	}
+	if (vmx->nested.virtual_apic_page) {
+		nested_release_page(vmx->nested.virtual_apic_page);
+		vmx->nested.virtual_apic_page = 0;
+	}
 
 	nested_free_all_saved_vmcss(vmx);
 }
@@ -6936,7 +6942,7 @@ static bool nested_vmx_exit_handled(struct kvm_vcpu *vcpu)
 	case EXIT_REASON_MCE_DURING_VMENTRY:
 		return 0;
 	case EXIT_REASON_TPR_BELOW_THRESHOLD:
-		return 1;
+		return nested_cpu_has(vmcs12, CPU_BASED_TPR_SHADOW);
 	case EXIT_REASON_APIC_ACCESS:
 		return nested_cpu_has2(vmcs12,
 			SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES);
@@ -7057,6 +7063,12 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu)
 
 static void update_cr8_intercept(struct kvm_vcpu *vcpu, int tpr, int irr)
 {
+	struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
+
+	if (is_guest_mode(vcpu) &&
+		nested_cpu_has(vmcs12, CPU_BASED_TPR_SHADOW))
+		return;
+
 	if (irr == -1 || tpr < irr) {
 		vmcs_write32(TPR_THRESHOLD, 0);
 		return;
@@ -8024,6 +8036,35 @@ static void prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
 	exec_control &= ~CPU_BASED_VIRTUAL_NMI_PENDING;
 	exec_control &= ~CPU_BASED_TPR_SHADOW;
 	exec_control |= vmcs12->cpu_based_vm_exec_control;
+
+	if (exec_control & CPU_BASED_TPR_SHADOW) {
+		if (vmx->nested.virtual_apic_page)
+			nested_release_page(vmx->nested.virtual_apic_page);
+		vmx->nested.virtual_apic_page =
+		   nested_get_page(vcpu, vmcs12->virtual_apic_page_addr);
+		if (!vmx->nested.virtual_apic_page)
+			exec_control &=
+				~CPU_BASED_TPR_SHADOW;
+		else
+			vmcs_write64(VIRTUAL_APIC_PAGE_ADDR,
+				page_to_phys(vmx->nested.virtual_apic_page));
+
+		/*
+		 * If CR8 load exits are enabled, CR8 store exits are enabled,
+		 * and virtualize APIC access is disabled, the processor would
+		 * never notice. Doing it unconditionally is not correct, but
+		 * it is the simplest thing.
+		 */
+		if (!(exec_control & CPU_BASED_TPR_SHADOW) &&
+			!((exec_control & CPU_BASED_CR8_LOAD_EXITING) &&
+				(exec_control & CPU_BASED_CR8_STORE_EXITING)))
+			nested_vmx_failValid(vcpu, VMXERR_ENTRY_INVALID_CONTROL_FIELD);
+
+		vmcs_write32(TPR_THRESHOLD, vmcs12->tpr_threshold);
+	} else if (vm_need_tpr_shadow(vmx->vcpu.kvm))
+		vmcs_write64(VIRTUAL_APIC_PAGE_ADDR,
+				__pa(vmx->vcpu.arch.apic->regs));
+
 	/*
 	 * Merging of IO and MSR bitmaps not currently supported.
 	 * Rather, exit every time.
@@ -8792,6 +8833,10 @@ static void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 exit_reason,
 		nested_release_page(vmx->nested.apic_access_page);
 		vmx->nested.apic_access_page = 0;
 	}
+	if (vmx->nested.virtual_apic_page) {
+		nested_release_page(vmx->nested.virtual_apic_page);
+		vmx->nested.virtual_apic_page = 0;
+	}
 
 	/*
 	 * Exiting from L2 to L1, we're now back to L1 which thinks it just
-- 
1.9.1

Re: [PATCH v4] KVM: nVMX: nested TPR shadow/threshold emulation

[Paolo Bonzini]

Il 19/08/2014 10:30, Wanpeng Li ha scritto:
> +		if (vmx->nested.virtual_apic_page)
> +			nested_release_page(vmx->nested.virtual_apic_page);
> +		vmx->nested.virtual_apic_page =
> +		   nested_get_page(vcpu, vmcs12->virtual_apic_page_addr);
> +		if (!vmx->nested.virtual_apic_page)
> +			exec_control &=
> +				~CPU_BASED_TPR_SHADOW;
> +		else
> +			vmcs_write64(VIRTUAL_APIC_PAGE_ADDR,
> +				page_to_phys(vmx->nested.virtual_apic_page));
> +
> +		/*
> +		 * If CR8 load exits are enabled, CR8 store exits are enabled,
> +		 * and virtualize APIC access is disabled, the processor would
> +		 * never notice. Doing it unconditionally is not correct, but
> +		 * it is the simplest thing.
> +		 */
> +		if (!(exec_control & CPU_BASED_TPR_SHADOW) &&
> +			!((exec_control & CPU_BASED_CR8_LOAD_EXITING) &&
> +				(exec_control & CPU_BASED_CR8_STORE_EXITING)))
> +			nested_vmx_failValid(vcpu, VMXERR_ENTRY_INVALID_CONTROL_FIELD);
> +

You aren't checking "virtualize APIC access" here, but the comment
mentions it.

As the comment says, failing the entry unconditionally could be the
simplest thing, which means moving the nested_vmx_failValid call inside
the "if (!vmx->nested.virtual_apic_page)".

If you want to check all of CR8_LOAD/CR8_STORE/VIRTUALIZE_APIC_ACCESS,
please mention in the comment that failing the vm entry is _not_ what
the processor does but it's basically the only possibility we have.  In
that case, I would also place the "if" within the "if
(!vmx->nested.virtual_apic_page)": it also simplifies the condition
because you don't have to check CPU_BASED_TPR_SHADOW anymore.

You can send v5 with these changes, and I'll apply it for 3.18.  Thanks!

Paolo

Re: [PATCH v4] KVM: nVMX: nested TPR shadow/threshold emulation

[Wanpeng Li]

Hi Paolo,
On Tue, Aug 19, 2014 at 10:34:20AM +0200, Paolo Bonzini wrote:
>Il 19/08/2014 10:30, Wanpeng Li ha scritto:
>> +		if (vmx->nested.virtual_apic_page)
>> +			nested_release_page(vmx->nested.virtual_apic_page);
>> +		vmx->nested.virtual_apic_page =
>> +		   nested_get_page(vcpu, vmcs12->virtual_apic_page_addr);
>> +		if (!vmx->nested.virtual_apic_page)
>> +			exec_control &=
>> +				~CPU_BASED_TPR_SHADOW;
>> +		else
>> +			vmcs_write64(VIRTUAL_APIC_PAGE_ADDR,
>> +				page_to_phys(vmx->nested.virtual_apic_page));
>> +
>> +		/*
>> +		 * If CR8 load exits are enabled, CR8 store exits are enabled,
>> +		 * and virtualize APIC access is disabled, the processor would
>> +		 * never notice. Doing it unconditionally is not correct, but
>> +		 * it is the simplest thing.
>> +		 */
>> +		if (!(exec_control & CPU_BASED_TPR_SHADOW) &&
>> +			!((exec_control & CPU_BASED_CR8_LOAD_EXITING) &&
>> +				(exec_control & CPU_BASED_CR8_STORE_EXITING)))
>> +			nested_vmx_failValid(vcpu, VMXERR_ENTRY_INVALID_CONTROL_FIELD);
>> +
>
>You aren't checking "virtualize APIC access" here, but the comment
>mentions it.
>
>As the comment says, failing the entry unconditionally could be the
>simplest thing, which means moving the nested_vmx_failValid call inside
>the "if (!vmx->nested.virtual_apic_page)".
>
>If you want to check all of CR8_LOAD/CR8_STORE/VIRTUALIZE_APIC_ACCESS,
>please mention in the comment that failing the vm entry is _not_ what
>the processor does but it's basically the only possibility we have.  In
>that case, I would also place the "if" within the "if
>(!vmx->nested.virtual_apic_page)": it also simplifies the condition
>because you don't have to check CPU_BASED_TPR_SHADOW anymore.
>
>You can send v5 with these changes, and I'll apply it for 3.18.  Thanks!
>

Do you mean this? 

+	/*
+	 * Failing the vm entry is _not_ what the processor does
+	 * but it's basically the only possibility we have.
+	 */
+	if (!vmx->nested.virtual_apic_page)
+		nested_vmx_failValid(vcpu, VMXERR_ENTRY_INVALID_CONTROL_FIELD);

Regards,
Wanpeng Li 

>Paolo

Re: [PATCH v4] KVM: nVMX: nested TPR shadow/threshold emulation

[Paolo Bonzini]

Il 20/08/2014 08:59, Wanpeng Li ha scritto:
> 
> +	/*
> +	 * Failing the vm entry is _not_ what the processor does
> +	 * but it's basically the only possibility we have.

	 * We could still enter the guest if CR8 load exits are 
	 * enabled, CR8 store exits are enabled, and virtualize APIC
	 * access is disabled; in this case the processor would never
	 * use the TPR shadow and we could simply clear the bit from
	 * the execution control.  But such a configuration is useless,
	 * so let's keep the code simple.

> +	 */
> +	if (!vmx->nested.virtual_apic_page)
> +		nested_vmx_failValid(vcpu, VMXERR_ENTRY_INVALID_CONTROL_FIELD);

I thought so, but I'm afraid it's too late to do nested_vmx_failValid 
here.

Without a test case, I'd be more confident if you moved the 
nested_release_page/nested_get_page to a separate function, that 
nested_vmx_run calls before enter_guest_mode.  The same function can 
map apic_access_page too, for cleanliness.  Something like this:

         if (cpu_has_secondary_exec_ctrls() &&
             nested_cpu_has(vmcs12,
                            CPU_BASED_ACTIVATE_SECONDARY_CONTROLS) &&
             (vmcs12->secondary_vm_exec_control &
              SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES)) {
                        if (vmx->nested.apic_access_page) /* shouldn't happen */
                                nested_release_page(vmx->nested.apic_access_page);
                        vmx->nested.apic_access_page =
                                nested_get_page(vcpu, vmcs12->apic_access_addr);
         }
        if (...) {
	         /* do the same for virtual_apic_page if CPU_BASED_TPR_SHADOW
	            is set... */

		/*
		 * Failing the vm entry is _not_ what the processor does
		 * but it's basically the only possibility we have.
		 * We could still enter the guest if CR8 load exits are 
		 * enabled, CR8 store exits are enabled, and virtualize APIC
		 * access is disabled; in this case the processor would never
		 * use the TPR shadow and we could simply clear the bit from
		 * the execution control.  But such a configuration is useless,
		 * so let's keep the code simple.
		 */
		if (!vmx->nested.virtual_apic_page)
			return -EFAULT;
	}

	return 0;

...

Then nested_vmx_run can do the nested_vmx_failValid if the function returns
an error.

Paolo