Re: [PATCH v3] KVM: nVMX: nested TPR shadow/threshold emulation

[Paolo Bonzini]

Il 05/08/2014 09:56, Zhang, Yang Z ha scritto:
> Wanpeng Li wrote on 2014-08-04:
>> 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.
>>
>> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxxxxxx>
>> ---
>> 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 | 38 ++++++++++++++++++++++++++++++++++++--
>>  1 file changed, 36 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index c604f3c..7a56e2c 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 +7063,9 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu)
>>
>>  static void update_cr8_intercept(struct kvm_vcpu *vcpu, int tpr, int irr)
>>  {
>> +	if (is_guest_mode(vcpu))
>> +		return;
>> +
>>  	if (irr == -1 || tpr < irr) {
>>  		vmcs_write32(TPR_THRESHOLD, 0);
>>  		return;
>> @@ -8024,6 +8033,27 @@ 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 (!(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);
> 
> I think this is not correct. The vmx->nested.virtual_apic_page may not valid due to two reasons:
> 1. The virtual_apic_page_addr is not a valid gfn. In this case, the vmx failure must be injected to L1 unconditionally regardless of the setting of CR8 load/store exiting.

You're right that accesses to the APIC-access page may also end up
writing to the virtual-APIC page.  Hence, if the "virtualize APIC
accesses" setting is 1 in the secondary exec controls, you also have to
fail the vmentry.

Doing it unconditionally is not correct, but it is the simplest thing to
do and it would be okay with a comment, I think.

> 2. The virtual_apic_page is swapped by L0. In this case, we should not inject failure to L1.

This cannot happen, nested_get_page ends up calling hva_to_pfn with
atomic==false, so the page would be swapped in and pinned.

>> +
>> +		vmcs_write32(TPR_THRESHOLD, vmcs12->tpr_threshold);
>> +	}
> 
> Miss else here:
> If L2 owns the APIC and doesn't use TPR_SHADOW, we need to setup the
> vmcs02 based on vmcs01. For example, if vmcs01 is using TPR_SHADOW, then
> vmcs02 must set it. Also, we need to use vmcs01's virtual_apic_page and
> TPR_THRESHOLD for vmcs02.

What do you mean by "owns the APIC"?

Paolo

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