linux-kernel - Re: [PATCH 2/2] KVM: x86: Add nested virtualization support for MPX

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Message-ID: <530CDD59.4040006@redhat.com>
Date:	Tue, 25 Feb 2014 19:13:45 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Jan Kiszka <jan.kiszka@...mens.com>, linux-kernel@...r.kernel.org
CC:	gleb@...nel.org, mtosatti@...hat.com,
	Liu Jinsong <jinsong.liu@...el.com>
Subject: Re: [PATCH 2/2] KVM: x86: Add nested virtualization support for MPX

Il 25/02/2014 19:05, Jan Kiszka ha scritto:
> On 2014-02-25 18:49, Paolo Bonzini wrote:
>> This is simple to do, the "host" BNDCFGS is either 0 or the guest value.
>> However, both controls have to be present.  We cannot provide MPX if
>> we only have one of the "load BNDCFGS" or "clear BNDCFGS" controls.
>>
>> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
>> ---
>>  arch/x86/kvm/vmx.c | 16 ++++++++++++++++
>>  1 file changed, 16 insertions(+)
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index 729b1e42aded..da28ac46ca88 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -202,6 +202,7 @@ struct __packed vmcs12 {
>>  	u64 guest_pdptr1;
>>  	u64 guest_pdptr2;
>>  	u64 guest_pdptr3;
>> +	u64 guest_bndcfgs;
>>  	u64 host_ia32_pat;
>>  	u64 host_ia32_efer;
>>  	u64 host_ia32_perf_global_ctrl;
>> @@ -534,6 +535,7 @@ static const unsigned long shadow_read_write_fields[] = {
>>  	GUEST_CS_LIMIT,
>>  	GUEST_CS_BASE,
>>  	GUEST_ES_BASE,
>> +	GUEST_BNDCFGS,
>>  	CR0_GUEST_HOST_MASK,
>>  	CR0_READ_SHADOW,
>>  	CR4_READ_SHADOW,
>> @@ -589,6 +591,7 @@ static const unsigned short vmcs_field_to_offset_table[] = {
>>  	FIELD64(GUEST_PDPTR1, guest_pdptr1),
>>  	FIELD64(GUEST_PDPTR2, guest_pdptr2),
>>  	FIELD64(GUEST_PDPTR3, guest_pdptr3),
>> +	FIELD64(GUEST_BNDCFGS, guest_bndcfgs),
>>  	FIELD64(HOST_IA32_PAT, host_ia32_pat),
>>  	FIELD64(HOST_IA32_EFER, host_ia32_efer),
>>  	FIELD64(HOST_IA32_PERF_GLOBAL_CTRL, host_ia32_perf_global_ctrl),
>> @@ -719,6 +722,7 @@ static unsigned long nested_ept_get_cr3(struct kvm_vcpu *vcpu);
>>  static u64 construct_eptp(unsigned long root_hpa);
>>  static void kvm_cpu_vmxon(u64 addr);
>>  static void kvm_cpu_vmxoff(void);
>> +static bool vmx_mpx_supported(void);
>>  static int vmx_set_tss_addr(struct kvm *kvm, unsigned int addr);
>>  static void vmx_set_segment(struct kvm_vcpu *vcpu,
>>  			    struct kvm_segment *var, int seg);
>> @@ -2279,6 +2283,8 @@ static __init void nested_vmx_setup_ctls_msrs(void)
>>  	}
>>  	nested_vmx_exit_ctls_high |= (VM_EXIT_ALWAYSON_WITHOUT_TRUE_MSR |
>>  		VM_EXIT_LOAD_IA32_EFER | VM_EXIT_SAVE_IA32_EFER);
>> +	if (vmx_mpx_supported())
>> +		nested_vmx_exit_ctls_high |= VM_EXIT_CLEAR_BNDCFGS;
>>
>>  	/* entry controls */
>>  	rdmsr(MSR_IA32_VMX_ENTRY_CTLS,
>> @@ -2292,6 +2298,8 @@ static __init void nested_vmx_setup_ctls_msrs(void)
>>  		VM_ENTRY_LOAD_IA32_PAT;
>>  	nested_vmx_entry_ctls_high |= (VM_ENTRY_ALWAYSON_WITHOUT_TRUE_MSR |
>>  				       VM_ENTRY_LOAD_IA32_EFER);
>> +	if (vmx_mpx_supported())
>> +		nested_vmx_entry_ctls_high |= VM_ENTRY_LOAD_BNDCFGS;
>>
>>  	/* cpu-based controls */
>>  	rdmsr(MSR_IA32_VMX_PROCBASED_CTLS,
>> @@ -7847,6 +7855,9 @@ static void prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
>>
>>  	set_cr4_guest_host_mask(vmx);
>>
>> +	if (vmcs12->vm_entry_controls & VM_ENTRY_LOAD_BNDCFGS)
>> +		vmcs_write64(GUEST_BNDCFGS, vmcs12->guest_bndcfgs);
>> +
>>  	if (vmcs12->cpu_based_vm_exec_control & CPU_BASED_USE_TSC_OFFSETING)
>>  		vmcs_write64(TSC_OFFSET,
>>  			vmx->nested.vmcs01_tsc_offset + vmcs12->tsc_offset);
>> @@ -8277,6 +8288,7 @@ static void prepare_vmcs12(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
>>  	vmcs12->guest_sysenter_cs = vmcs_read32(GUEST_SYSENTER_CS);
>>  	vmcs12->guest_sysenter_esp = vmcs_readl(GUEST_SYSENTER_ESP);
>>  	vmcs12->guest_sysenter_eip = vmcs_readl(GUEST_SYSENTER_EIP);
>> +	vmcs12->guest_bndcfgs = vmcs_readl(GUEST_BNDCFGS);
>
> Can we read this value unconditionally, even when the host does not
> support the feature?

return -EWRONGPATCH;

>>
>>  	/* update exit information fields: */
>>
>> @@ -8386,6 +8398,10 @@ static void load_vmcs12_host_state(struct kvm_vcpu *vcpu,
>>  	vmcs_writel(GUEST_IDTR_BASE, vmcs12->host_idtr_base);
>>  	vmcs_writel(GUEST_GDTR_BASE, vmcs12->host_gdtr_base);
>>
>> +	/* If not VM_EXIT_CLEAR_BNDCFGS, the L2 value propagates to L1.  */
>> +	if (vmcs12->vm_exit_controls & VM_EXIT_CLEAR_BNDCFGS)
>> +		vmcs_write64(GUEST_BNDCFGS, 0);
>> +
>>  	if (vmcs12->vm_exit_controls & VM_EXIT_LOAD_IA32_PAT) {
>>  		vmcs_write64(GUEST_IA32_PAT, vmcs12->host_ia32_pat);
>>  		vcpu->arch.pat = vmcs12->host_ia32_pat;
>>
>
> Do we also have a unit test to stress this? Or are we lacking silicon
> with MPX and corresponding VMX features?

No silicon yet.

There is an emulator, but it is already slow enough without nested 
virtualization... it would be three-level virtualization :)

Paolo

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