[Xen-changelog] [xen stable-4.6] x86/hvm: Permit guests direct access to MSR_{SPEC_CTRL, PRED_CMD}

[patchbot@xxxxxxx]

commit 44c2666589fefc13049edc874c7ef063823bad90
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Wed Feb 14 13:40:38 2018 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Feb 14 13:40:38 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/hvm/svm/svm.c      | 13 +++++++++++++
 xen/arch/x86/hvm/vmx/vmcs.c     | 30 ++++++++++++++++++++++++++++++
 xen/include/asm-x86/processor.h |  2 ++
 3 files changed, 45 insertions(+)

diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index 7b51542..d84e150 100644
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -1043,6 +1043,19 @@ static void noreturn svm_do_resume(struct vcpu *v)
     if ( nestedhvm_enabled(v->domain) && nestedhvm_vcpu_in_guestmode(v) )
         vcpu_guestmode = 1;
 
+    if ( !(v->arch.flags & TF_launched) )
+    {
+        uint32_t ebx, dummy;
+
+        /* 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);
+
+        v->arch.flags |= TF_launched;
+    }
+
     if ( !vcpu_guestmode &&
         unlikely(v->arch.hvm_vcpu.debug_state_latch != debug_state) )
     {
diff --git a/xen/arch/x86/hvm/vmx/vmcs.c b/xen/arch/x86/hvm/vmx/vmcs.c
index b297a91..cf15a62 100644
--- a/xen/arch/x86/hvm/vmx/vmcs.c
+++ b/xen/arch/x86/hvm/vmx/vmcs.c
@@ -1664,6 +1664,36 @@ void vmx_do_resume(struct vcpu *v)
         hvm_asid_flush_vcpu(v);
     }
 
+    if ( !(v->arch.flags & TF_launched) )
+    {
+        uint32_t _7d0, e8b, dummy;
+
+        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);
+
+        v->arch.flags |= TF_launched;
+    }
+
     debug_state = v->domain->debugger_attached
                   || v->domain->arch.monitor.software_breakpoint_enabled
                   || v->domain->arch.monitor.singlestep_enabled;
diff --git a/xen/include/asm-x86/processor.h b/xen/include/asm-x86/processor.h
index 246db8f..cd8ad52 100644
--- a/xen/include/asm-x86/processor.h
+++ b/xen/include/asm-x86/processor.h
@@ -133,6 +133,8 @@
 /* 'arch_vcpu' flags values */
 #define _TF_kernel_mode        0
 #define TF_kernel_mode         (1<<_TF_kernel_mode)
+#define _TF_launched           1
+#define TF_launched            (1u << _TF_launched)
 
 /* #PF error code values. */
 #define PFEC_page_present   (_AC(1,U) << 0)
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.6

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