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

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Message-ID: <530CDB5D.6020304@siemens.com>
Date:	Tue, 25 Feb 2014 19:05:17 +0100
From:	Jan Kiszka <jan.kiszka@...mens.com>
To:	Paolo Bonzini <pbonzini@...hat.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

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?

>  
>  	/* 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?

Jan

-- 
Siemens AG, Corporate Technology, CT RTC ITP SES-DE
Corporate Competence Center Embedded Linux
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