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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCH v6.5 19/26] x86/hvm: Permit guests direct access to MSR_{SPEC_CTRL, PRED_CMD}
For performance reasons, HVM guests should have direct access to these MSRs
when possible.
Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
v4:
* Redo almost from scratch to support AMD
v6:
* Allow direct access to PRED_CMD for IBPB
---
xen/arch/x86/domctl.c | 19 +++++++++++++++++++
xen/arch/x86/hvm/svm/svm.c | 5 +++++
xen/arch/x86/hvm/vmx/vmx.c | 18 ++++++++++++++++++
xen/arch/x86/msr.c | 3 ++-
xen/include/asm-x86/msr.h | 5 ++++-
5 files changed, 48 insertions(+), 2 deletions(-)
diff --git a/xen/arch/x86/domctl.c b/xen/arch/x86/domctl.c
index 72b4489..81fbeaa 100644
--- a/xen/arch/x86/domctl.c
+++ b/xen/arch/x86/domctl.c
@@ -53,6 +53,7 @@ static int update_domain_cpuid_info(struct domain *d,
struct cpuid_policy *p = d->arch.cpuid;
const struct cpuid_leaf leaf = { ctl->eax, ctl->ebx, ctl->ecx, ctl->edx };
int old_vendor = p->x86_vendor;
+ unsigned int old_7d0 = p->feat.raw[0].d, old_e8b = p->extd.raw[8].b;
bool call_policy_changed = false; /* Avoid for_each_vcpu() unnecessarily */
/*
@@ -218,6 +219,14 @@ static int update_domain_cpuid_info(struct domain *d,
d->arch.pv_domain.cpuidmasks->_7ab0 = mask;
}
+
+ /*
+ * If the IBSRB/STIBP policy has changed, we need to recalculate the
+ * MSR interception bitmaps and STIBP protection default.
+ */
+ call_policy_changed = ((old_7d0 ^ p->feat.raw[0].d) &
+ (cpufeat_mask(X86_FEATURE_IBRSB) |
+ cpufeat_mask(X86_FEATURE_STIBP)));
break;
case 0xa:
@@ -292,6 +301,16 @@ static int update_domain_cpuid_info(struct domain *d,
d->arch.pv_domain.cpuidmasks->e1cd = mask;
}
break;
+
+ case 0x80000008:
+ /*
+ * If the IBRB policy has changed, we need to recalculate the MSR
+ * interception bitmaps.
+ */
+ call_policy_changed = (is_hvm_domain(d) &&
+ ((old_e8b ^ p->extd.raw[8].b) &
+ (cpufeat_mask(X86_FEATURE_IBPB))));
+ break;
}
if ( call_policy_changed )
diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index c48fdfa..ee47508 100644
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -617,6 +617,7 @@ static void svm_cpuid_policy_changed(struct vcpu *v)
{
struct arch_svm_struct *arch_svm = &v->arch.hvm_svm;
struct vmcb_struct *vmcb = arch_svm->vmcb;
+ const struct cpuid_policy *cp = v->domain->arch.cpuid;
u32 bitmap = vmcb_get_exception_intercepts(vmcb);
if ( opt_hvm_fep ||
@@ -626,6 +627,10 @@ static void svm_cpuid_policy_changed(struct vcpu *v)
bitmap &= ~(1U << TRAP_invalid_op);
vmcb_set_exception_intercepts(vmcb, bitmap);
+
+ /* Give access to MSR_PRED_CMD if the guest has been told about it. */
+ svm_intercept_msr(v, MSR_PRED_CMD,
+ cp->extd.ibpb ? MSR_INTERCEPT_NONE : MSR_INTERCEPT_RW);
}
static void svm_sync_vmcb(struct vcpu *v)
diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index e036303..8609de3 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -656,6 +656,8 @@ void vmx_update_exception_bitmap(struct vcpu *v)
static void vmx_cpuid_policy_changed(struct vcpu *v)
{
+ const struct cpuid_policy *cp = v->domain->arch.cpuid;
+
if ( opt_hvm_fep ||
(v->domain->arch.cpuid->x86_vendor != boot_cpu_data.x86_vendor) )
v->arch.hvm_vmx.exception_bitmap |= (1U << TRAP_invalid_op);
@@ -665,6 +667,22 @@ static void vmx_cpuid_policy_changed(struct vcpu *v)
vmx_vmcs_enter(v);
vmx_update_exception_bitmap(v);
vmx_vmcs_exit(v);
+
+ /*
+ * We can only pass though MSR_SPEC_CTRL if the guest knows about all bits
+ * in it. Otherwise, Xen may be fixing up in the background.
+ */
+ v->arch.msr->spec_ctrl.direct_access = cp->feat.ibrsb && cp->feat.stibp;
+ if ( v->arch.msr->spec_ctrl.direct_access )
+ vmx_clear_msr_intercept(v, MSR_SPEC_CTRL, VMX_MSR_RW);
+ else
+ vmx_set_msr_intercept(v, MSR_SPEC_CTRL, VMX_MSR_RW);
+
+ /* MSR_PRED_CMD is safe to pass through if the guest knows about it. */
+ if ( cp->feat.ibrsb || cp->extd.ibpb )
+ vmx_clear_msr_intercept(v, MSR_PRED_CMD, VMX_MSR_RW);
+ else
+ vmx_set_msr_intercept(v, MSR_PRED_CMD, VMX_MSR_RW);
}
int vmx_guest_x86_mode(struct vcpu *v)
diff --git a/xen/arch/x86/msr.c b/xen/arch/x86/msr.c
index 02a7b49..697cc6e 100644
--- a/xen/arch/x86/msr.c
+++ b/xen/arch/x86/msr.c
@@ -132,7 +132,8 @@ int guest_rdmsr(const struct vcpu *v, uint32_t msr,
uint64_t *val)
case MSR_SPEC_CTRL:
if ( !cp->feat.ibrsb )
goto gp_fault;
- *val = vp->spec_ctrl.guest;
+ *val = (vp->spec_ctrl.direct_access
+ ? vp->spec_ctrl.host : vp->spec_ctrl.guest);
break;
case MSR_INTEL_PLATFORM_INFO:
diff --git a/xen/include/asm-x86/msr.h b/xen/include/asm-x86/msr.h
index 3d0012d..007e966 100644
--- a/xen/include/asm-x86/msr.h
+++ b/xen/include/asm-x86/msr.h
@@ -229,10 +229,13 @@ struct msr_vcpu_policy
* Only the bottom two bits are defined, so no need to waste space
* with uint64_t at the moment. We maintain the guests idea of the
* value it wrote, and a value to install into hardware (extended to
- * uint32_t to simplify the asm) which might be different.
+ * uint32_t to simplify the asm) which might be different. HVM guests
+ * might be given direct access to the MSRs, at which point the
+ * 'guest' value becomes stale.
*/
uint32_t host;
uint8_t guest;
+ bool direct_access;
} spec_ctrl;
/* 0x00000140 MSR_INTEL_MISC_FEATURES_ENABLES */
--
2.1.4
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