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KVM: x86: handle missing MPX in nested virtualization

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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: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2014-03-05 23:19:52 +01:00
parent 36be0b9deb
commit 93c4adc7af
4 changed files with 30 additions and 3 deletions
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5
arch/x86/kvm/cpuid.c
View File

@ -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 =

6
arch/x86/kvm/svm.c
View File

@ -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,

5
arch/x86/kvm/vmx.c
View File

@ -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:

17
arch/x86/kvm/x86.c
View File

@ -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++;