[Xen-changelog] [xen stable-4.8] x86/hvm: Permit guests direct access to MSR_{SPEC_CTRL, PRED_CMD}

[patchbot@xxxxxxx]

commit ff570a3ee0b42a036df1e8c2b05730192ad4bd90
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Thu Feb 8 12:53:40 2018 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Feb 8 12:53:40 2018 +0100

    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>
    Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
    master commit: 5a2fe171144ebcc908ea1fca45058d6010f6a286
    master date: 2018-01-26 14:10:21 +0000
---
 xen/arch/x86/domctl.c      | 13 +++++++++++++
 xen/arch/x86/hvm/svm/svm.c |  7 +++++++
 xen/arch/x86/hvm/vmx/vmx.c | 21 +++++++++++++++++++++
 3 files changed, 41 insertions(+)

diff --git a/xen/arch/x86/domctl.c b/xen/arch/x86/domctl.c
index 7b2dddc..0c9fe39 100644
--- a/xen/arch/x86/domctl.c
+++ b/xen/arch/x86/domctl.c
@@ -181,6 +181,11 @@ static void update_domain_cpuid_info(struct domain *d,
         else
             ctl->edx &= ~cpufeat_mask(X86_FEATURE_STIBP);
 
+        /*
+         * If the IBRS/IBPB policy has changed, we need to recalculate the MSR
+         * interception bitmaps.
+         */
+        call_policy_changed = is_hvm_domain(d);
         break;
 
     case 0xd:
@@ -241,6 +246,14 @@ static void update_domain_cpuid_info(struct domain *d,
             d->arch.pv_domain.cpuidmasks->e1cd = mask;
         }
         break;
+
+    case 0x80000008:
+        /*
+         * If the IBPB policy has changed, we need to recalculate the MSR
+         * interception bitmaps.
+         */
+        call_policy_changed = is_hvm_domain(d);
+        break;
     }
 
     if ( call_policy_changed )
diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index 1b84aa6..19e0265 100644
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -612,6 +612,7 @@ 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;
     u32 bitmap = vmcb_get_exception_intercepts(vmcb);
+    uint32_t ebx, dummy;
 
     if ( opt_hvm_fep ||
          (v->domain->arch.x86_vendor != boot_cpu_data.x86_vendor) )
@@ -620,6 +621,12 @@ 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. */
+    domain_cpuid(v->domain, 0x80000008, 0, &dummy, &ebx, &dummy, &dummy);
+    svm_intercept_msr(v, MSR_PRED_CMD,
+                      ebx & cpufeat_mask(X86_FEATURE_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 e217a09..eb67cb9 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -545,6 +545,8 @@ void vmx_update_exception_bitmap(struct vcpu *v)
 
 static void vmx_cpuid_policy_changed(struct vcpu *v)
 {
+    uint32_t _7d0, e8b, dummy;
+
     if ( opt_hvm_fep ||
          (v->domain->arch.x86_vendor != boot_cpu_data.x86_vendor) )
         v->arch.hvm_vmx.exception_bitmap |= (1U << TRAP_invalid_op);
@@ -554,6 +556,25 @@ static void vmx_cpuid_policy_changed(struct vcpu *v)
     vmx_vmcs_enter(v);
     vmx_update_exception_bitmap(v);
     vmx_vmcs_exit(v);
+
+    domain_cpuid(v->domain, 7, 0, &dummy, &dummy, &dummy, &_7d0);
+    domain_cpuid(v->domain, 0x80000008, 0, &dummy, &e8b, &dummy, &dummy);
+
+    /*
+     * We can safely pass MSR_SPEC_CTRL through to the guest, even if STIBP
+     * isn't enumerated in hardware, as SPEC_CTRL_STIBP is ignored.
+     */
+    if ( _7d0 & cpufeat_mask(X86_FEATURE_IBRSB) )
+        vmx_disable_intercept_for_msr(v, MSR_SPEC_CTRL, MSR_TYPE_R | 
MSR_TYPE_W);
+    else
+        vmx_enable_intercept_for_msr(v, MSR_SPEC_CTRL, MSR_TYPE_R | 
MSR_TYPE_W);
+
+    /* MSR_PRED_CMD is safe to pass through if the guest knows about it. */
+    if ( (_7d0 & cpufeat_mask(X86_FEATURE_IBRSB)) ||
+         (e8b & cpufeat_mask(X86_FEATURE_IBPB)) )
+        vmx_disable_intercept_for_msr(v, MSR_PRED_CMD, MSR_TYPE_R | 
MSR_TYPE_W);
+    else
+        vmx_enable_intercept_for_msr(v, MSR_PRED_CMD, MSR_TYPE_R | MSR_TYPE_W);
 }
 
 static int vmx_guest_x86_mode(struct vcpu *v)
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.8

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