x86/guest: Introduce {get,set}_reg() infrastructure

Various registers have per-guest-type or per-vendor locations or access
requirements.  To support their use from common code, provide accessors which
allow for per-guest-type behaviour.

For now, just infrastructure handling default cases and expectations.
Subsequent patches will start handling registers using this infrastructure.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
master commit: 88d3ff7ab1
master date: 2022-01-20 16:32:11 +0000

xen/arch/x86/hvm/hvm.c

@@ -3724,6 +3724,28 @@ gp_fault:
     return X86EMUL_EXCEPTION;
 }
 
+uint64_t hvm_get_reg(struct vcpu *v, unsigned int reg)
+{
+    ASSERT(v == current || !vcpu_runnable(v));
+
+    switch ( reg )
+    {
+    default:
+        return alternative_call(hvm_funcs.get_reg, v, reg);
+    }
+}
+
+void hvm_set_reg(struct vcpu *v, unsigned int reg, uint64_t val)
+{
+    ASSERT(v == current || !vcpu_runnable(v));
+
+    switch ( reg )
+    {
+    default:
+        return alternative_vcall(hvm_funcs.set_reg, v, reg, val);
+    }
+}
+
 static bool is_sysdesc_access(const struct x86_emulate_state *state,
                               const struct x86_emulate_ctxt *ctxt)
 {

xen/arch/x86/hvm/svm/svm.c

@@ -2415,6 +2415,33 @@ static bool svm_get_pending_event(struct vcpu *v, struct x86_event *info)
     return true;
 }
 
+static uint64_t svm_get_reg(struct vcpu *v, unsigned int reg)
+{
+    struct domain *d = v->domain;
+
+    switch ( reg )
+    {
+    default:
+        printk(XENLOG_G_ERR "%s(%pv, 0x%08x) Bad register\n",
+               __func__, v, reg);
+        domain_crash(d);
+        return 0;
+    }
+}
+
+static void svm_set_reg(struct vcpu *v, unsigned int reg, uint64_t val)
+{
+    struct domain *d = v->domain;
+
+    switch ( reg )
+    {
+    default:
+        printk(XENLOG_G_ERR "%s(%pv, 0x%08x, 0x%016"PRIx64") Bad register\n",
+               __func__, v, reg, val);
+        domain_crash(d);
+    }
+}
+
 static struct hvm_function_table __initdata svm_function_table = {
     .name                 = "SVM",
     .cpu_up_prepare       = svm_cpu_up_prepare,
@@ -2464,6 +2491,9 @@ static struct hvm_function_table __initdata svm_function_table = {
     .nhvm_intr_blocked = nsvm_intr_blocked,
     .nhvm_hap_walk_L1_p2m = nsvm_hap_walk_L1_p2m,
 
+    .get_reg = svm_get_reg,
+    .set_reg = svm_set_reg,
+
     .tsc_scaling = {
         .max_ratio = ~TSC_RATIO_RSVD_BITS,
     },

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

@@ -2240,6 +2240,33 @@ static bool vmx_get_pending_event(struct vcpu *v, struct x86_event *info)
     return true;
 }
 
+static uint64_t vmx_get_reg(struct vcpu *v, unsigned int reg)
+{
+    struct domain *d = v->domain;
+
+    switch ( reg )
+    {
+    default:
+        printk(XENLOG_G_ERR "%s(%pv, 0x%08x) Bad register\n",
+               __func__, v, reg);
+        domain_crash(d);
+        return 0;
+    }
+}
+
+static void vmx_set_reg(struct vcpu *v, unsigned int reg, uint64_t val)
+{
+    struct domain *d = v->domain;
+
+    switch ( reg )
+    {
+    default:
+        printk(XENLOG_G_ERR "%s(%pv, 0x%08x, 0x%016"PRIx64") Bad register\n",
+               __func__, v, reg, val);
+        domain_crash(d);
+    }
+}
+
 static struct hvm_function_table __initdata vmx_function_table = {
     .name                 = "VMX",
     .cpu_up_prepare       = vmx_cpu_up_prepare,
@@ -2295,6 +2322,10 @@ static struct hvm_function_table __initdata vmx_function_table = {
     .altp2m_vcpu_update_vmfunc_ve = vmx_vcpu_update_vmfunc_ve,
     .altp2m_vcpu_emulate_ve = vmx_vcpu_emulate_ve,
     .altp2m_vcpu_emulate_vmfunc = vmx_vcpu_emulate_vmfunc,
+
+    .get_reg = vmx_get_reg,
+    .set_reg = vmx_set_reg,
+
     .tsc_scaling = {
         .max_ratio = VMX_TSC_MULTIPLIER_MAX,
     },

xen/arch/x86/pv/emulate.c

@@ -90,6 +90,37 @@ void pv_emul_instruction_done(struct cpu_user_regs *regs, unsigned long rip)
     }
 }
 
+uint64_t pv_get_reg(struct vcpu *v, unsigned int reg)
+{
+    struct domain *d = v->domain;
+
+    ASSERT(v == current || !vcpu_runnable(v));
+
+    switch ( reg )
+    {
+    default:
+        printk(XENLOG_G_ERR "%s(%pv, 0x%08x) Bad register\n",
+               __func__, v, reg);
+        domain_crash(d);
+        return 0;
+    }
+}
+
+void pv_set_reg(struct vcpu *v, unsigned int reg, uint64_t val)
+{
+    struct domain *d = v->domain;
+
+    ASSERT(v == current || !vcpu_runnable(v));
+
+    switch ( reg )
+    {
+    default:
+        printk(XENLOG_G_ERR "%s(%pv, 0x%08x, 0x%016"PRIx64") Bad register\n",
+               __func__, v, reg, val);
+        domain_crash(d);
+    }
+}
+
 /*
  * Local variables:
  * mode: C

xen/include/asm-x86/hvm/hvm.h

@@ -214,6 +214,9 @@ struct hvm_function_table {
     bool_t (*altp2m_vcpu_emulate_ve)(struct vcpu *v);
     int (*altp2m_vcpu_emulate_vmfunc)(const struct cpu_user_regs *regs);
 
+    uint64_t (*get_reg)(struct vcpu *v, unsigned int reg);
+    void (*set_reg)(struct vcpu *v, unsigned int reg, uint64_t val);
+
     /*
      * Parameters and callbacks for hardware-assisted TSC scaling,
      * which are valid only when the hardware feature is available.
@@ -655,6 +658,18 @@ static inline bool altp2m_vcpu_emulate_ve(struct vcpu *v)
     return false;
 }
 
+/*
+ * Accessors for registers which have per-guest-type or per-vendor locations
+ * (e.g. VMCS, msr load/save lists, VMCB, VMLOAD lazy, etc).
+ *
+ * The caller is responsible for all auditing - these accessors do not fail,
+ * but do use domain_crash() for usage errors.
+ *
+ * Must cope with being called in non-current context.
+ */
+uint64_t hvm_get_reg(struct vcpu *v, unsigned int reg);
+void hvm_set_reg(struct vcpu *v, unsigned int reg, uint64_t val);
+
 /*
  * This must be defined as a macro instead of an inline function,
  * because it uses 'struct vcpu' and 'struct domain' which have

xen/include/asm-x86/pv/domain.h

@@ -65,6 +65,10 @@ static inline unsigned long get_pcid_bits(const struct vcpu *v, bool is_xpti)
 #endif
 }
 
+/* See hvm_{get,set}_reg() for description. */
+uint64_t pv_get_reg(struct vcpu *v, unsigned int reg);
+void pv_set_reg(struct vcpu *v, unsigned int reg, uint64_t val);
+
 #ifdef CONFIG_PV
 
 void pv_vcpu_destroy(struct vcpu *v);