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Commit 93c4adc7 authored by Paolo Bonzini's avatar Paolo Bonzini
Browse files

KVM: x86: handle missing MPX in nested virtualization 



When doing nested virtualization, we may be able to read BNDCFGS but
still not be allowed to write to GUEST_BNDCFGS in the VMCS.  Guard
writes to the field with vmx_mpx_supported(), and similarly hide the
MSR from userspace if the processor does not support the field.

We could work around this with the generic MSR save/load machinery,
but there is only a limited number of MSR save/load slots and it is
not really worthwhile to waste one for a scenario that should not
happen except in the nested virtualization case.

Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 36be0b9d

arch/x86/kvm/cpuid.c

+2 −3
Original line number Diff line number Diff line
@@ -47,7 +47,7 @@ u64 kvm_supported_xcr0(void) 
{

	u64 xcr0 = KVM_SUPPORTED_XCR0 & host_xcr0;



	if (!kvm_x86_ops->mpx_supported || !kvm_x86_ops->mpx_supported())

	if (!kvm_x86_ops->mpx_supported())

		xcr0 &= ~(XSTATE_BNDREGS | XSTATE_BNDCSR);



	return xcr0;
@@ -259,8 +259,7 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function, 
#endif

	unsigned f_rdtscp = kvm_x86_ops->rdtscp_supported() ? F(RDTSCP) : 0;

	unsigned f_invpcid = kvm_x86_ops->invpcid_supported() ? F(INVPCID) : 0;

	unsigned f_mpx = kvm_x86_ops->mpx_supported ?

			 (kvm_x86_ops->mpx_supported() ? F(MPX) : 0) : 0;

	unsigned f_mpx = kvm_x86_ops->mpx_supported() ? F(MPX) : 0;



	/* cpuid 1.edx */

	const u32 kvm_supported_word0_x86_features =

arch/x86/kvm/svm.c

+6 −0
Original line number Diff line number Diff line
@@ -4089,6 +4089,11 @@ static bool svm_invpcid_supported(void) 
	return false;

}



static bool svm_mpx_supported(void)

{

	return false;

}



static bool svm_has_wbinvd_exit(void)

{

	return true;
@@ -4371,6 +4376,7 @@ static struct kvm_x86_ops svm_x86_ops = { 


	.rdtscp_supported = svm_rdtscp_supported,

	.invpcid_supported = svm_invpcid_supported,

	.mpx_supported = svm_mpx_supported,



	.set_supported_cpuid = svm_set_supported_cpuid,

arch/x86/kvm/vmx.c

+5 −0
Original line number Diff line number Diff line
@@ -729,6 +729,7 @@ 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);
@@ -2501,6 +2502,8 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 *pdata) 
		data = vmcs_readl(GUEST_SYSENTER_ESP);

		break;

	case MSR_IA32_BNDCFGS:

		if (!vmx_mpx_supported())

			return 1;

		data = vmcs_read64(GUEST_BNDCFGS);

		break;

	case MSR_IA32_FEATURE_CONTROL:
@@ -2572,6 +2575,8 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) 
		vmcs_writel(GUEST_SYSENTER_ESP, data);

		break;

	case MSR_IA32_BNDCFGS:

		if (!vmx_mpx_supported())

			return 1;

		vmcs_write64(GUEST_BNDCFGS, data);

		break;

	case MSR_IA32_TSC:

arch/x86/kvm/x86.c

+17 −0
Original line number Diff line number Diff line
@@ -3937,6 +3937,23 @@ static void kvm_init_msr_list(void) 
	for (i = j = KVM_SAVE_MSRS_BEGIN; i < ARRAY_SIZE(msrs_to_save); i++) {

		if (rdmsr_safe(msrs_to_save[i], &dummy[0], &dummy[1]) < 0)

			continue;



		/*

		 * Even MSRs that are valid in the host may not be exposed

		 * to the guests in some cases.  We could work around this

		 * in VMX with the generic MSR save/load machinery, but it

		 * is not really worthwhile since it will really only

		 * happen with nested virtualization.

		 */

		switch (msrs_to_save[i]) {

		case MSR_IA32_BNDCFGS:

			if (!kvm_x86_ops->mpx_supported())

				continue;

			break;

		default:

			break;

		}



		if (j < i)

			msrs_to_save[j] = msrs_to_save[i];

		j++;