x86/msr: Split MSR_SPEC_CTRL handling

In order to fix a VT-x bug, and support MSR_SPEC_CTRL on AMD, move
MSR_SPEC_CTRL handling into the new {pv,hvm}_{get,set}_reg() infrastructure.

Duplicate the msrs->spec_ctrl.raw accesses in the PV and VT-x paths for now.
The SVM path is currently unreachable because of the CPUID policy.

No functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

xen/arch/x86/hvm/vmx/vmx.c

@@ -2405,6 +2405,9 @@ static uint64_t vmx_get_reg(struct vcpu *v, unsigned int reg)
 
     switch ( reg )
     {
+    case MSR_SPEC_CTRL:
+        return v->arch.msrs->spec_ctrl.raw;
+
     default:
         printk(XENLOG_G_ERR "%s(%pv, 0x%08x) Bad register\n",
                __func__, v, reg);
@@ -2419,6 +2422,10 @@ static void vmx_set_reg(struct vcpu *v, unsigned int reg, uint64_t val)
 
     switch ( reg )
     {
+    case MSR_SPEC_CTRL:
+        v->arch.msrs->spec_ctrl.raw = val;
+        break;
+
     default:
         printk(XENLOG_G_ERR "%s(%pv, 0x%08x, 0x%016"PRIx64") Bad register\n",
                __func__, v, reg, val);

xen/arch/x86/msr.c

@@ -28,6 +28,7 @@
 #include <asm/hvm/nestedhvm.h>
 #include <asm/hvm/viridian.h>
 #include <asm/msr.h>
+#include <asm/pv/domain.h>
 #include <asm/setup.h>
 
 #include <public/hvm/params.h>
@@ -265,8 +266,7 @@ int guest_rdmsr(struct vcpu *v, uint32_t msr, uint64_t *val)
     case MSR_SPEC_CTRL:
         if ( !cp->feat.ibrsb )
             goto gp_fault;
-        *val = msrs->spec_ctrl.raw;
-        break;
+        goto get_reg;
 
     case MSR_INTEL_PLATFORM_INFO:
         *val = mp->platform_info.raw;
@@ -424,6 +424,13 @@ int guest_rdmsr(struct vcpu *v, uint32_t msr, uint64_t *val)
 
     return ret;
 
+ get_reg: /* Delegate register access to per-vm-type logic. */
+    if ( is_pv_domain(d) )
+        *val = pv_get_reg(v, msr);
+    else
+        *val = hvm_get_reg(v, msr);
+    return X86EMUL_OKAY;
+
  gp_fault:
     return X86EMUL_EXCEPTION;
 }
@@ -513,9 +520,7 @@ int guest_wrmsr(struct vcpu *v, uint32_t msr, uint64_t val)
 
         if ( val & rsvd )
             goto gp_fault; /* Rsvd bit set? */
-
-        msrs->spec_ctrl.raw = val;
-        break;
+        goto set_reg;
 
     case MSR_PRED_CMD:
         if ( !cp->feat.ibrsb && !cp->extd.ibpb )
@@ -663,6 +668,13 @@ int guest_wrmsr(struct vcpu *v, uint32_t msr, uint64_t val)
 
     return ret;
 
+ set_reg: /* Delegate register access to per-vm-type logic. */
+    if ( is_pv_domain(d) )
+        pv_set_reg(v, msr, val);
+    else
+        hvm_set_reg(v, msr, val);
+    return X86EMUL_OKAY;
+
  gp_fault:
     return X86EMUL_EXCEPTION;
 }

xen/arch/x86/pv/emulate.c

@@ -92,12 +92,16 @@ void pv_emul_instruction_done(struct cpu_user_regs *regs, unsigned long rip)
 
 uint64_t pv_get_reg(struct vcpu *v, unsigned int reg)
 {
+    const struct vcpu_msrs *msrs = v->arch.msrs;
     struct domain *d = v->domain;
 
     ASSERT(v == current || !vcpu_runnable(v));
 
     switch ( reg )
     {
+    case MSR_SPEC_CTRL:
+        return msrs->spec_ctrl.raw;
+
     default:
         printk(XENLOG_G_ERR "%s(%pv, 0x%08x) Bad register\n",
                __func__, v, reg);
@@ -108,12 +112,17 @@ uint64_t pv_get_reg(struct vcpu *v, unsigned int reg)
 
 void pv_set_reg(struct vcpu *v, unsigned int reg, uint64_t val)
 {
+    struct vcpu_msrs *msrs = v->arch.msrs;
     struct domain *d = v->domain;
 
     ASSERT(v == current || !vcpu_runnable(v));
 
     switch ( reg )
     {
+    case MSR_SPEC_CTRL:
+        msrs->spec_ctrl.raw = val;
+        break;
+
     default:
         printk(XENLOG_G_ERR "%s(%pv, 0x%08x, 0x%016"PRIx64") Bad register\n",
                __func__, v, reg, val);