x86/traps: const-correctness for IST handlers

NMI and MCE interrupt handlers have no right to modify their exception frame
or underlying vcpu registers.  Apply liberal quantities of 'const' to 'struct
cpu_user_regs *' throughout the codebase.

The Double Fault handler, while an IST handler, reloads some extra
architectural state back into its regs parameter.  As this is for printing
purposes and on a terminal error path, the const requirements for #DF are
relaxed.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

xen/arch/x86/alternative.c

@@ -78,7 +78,7 @@ static const unsigned char * const p6_nops[ASM_NOP_MAX+1] /*__initconst*/ = {
 
 static const unsigned char * const *ideal_nops __initdata = k8_nops;
 
-static int __init mask_nmi_callback(struct cpu_user_regs *regs, int cpu)
+static int __init mask_nmi_callback(const struct cpu_user_regs *regs, int cpu)
 {
     return 1;
 }

xen/arch/x86/cpu/mcheck/mcaction.c

@@ -38,7 +38,7 @@ void mce_register_addrcheck(mce_check_addr_t cbfunc)
 void
 mc_memerr_dhandler(struct mca_binfo *binfo,
                    enum mce_result *result,
-                   struct cpu_user_regs *regs)
+                   const struct cpu_user_regs *regs)
 {
     struct mcinfo_bank *bank = binfo->mib;
     struct mcinfo_global *global = binfo->mig;

xen/arch/x86/cpu/mcheck/mcaction.h

@@ -7,7 +7,7 @@
 void
 mc_memerr_dhandler(struct mca_binfo *binfo,
                    enum mce_result *result,
-                   struct cpu_user_regs *regs);
+                   const struct cpu_user_regs *regs);
 
 #define MC_ADDR_PHYSICAL  0
 #define MC_ADDR_VIRTUAL   1

xen/arch/x86/cpu/mcheck/mce.c

@@ -70,7 +70,7 @@ static void __init mce_set_verbosity(char *str)
 custom_param("mce_verbosity", mce_set_verbosity);
 
 /* Handle unconfigured int18 (should never happen) */
-static void unexpected_machine_check(struct cpu_user_regs *regs, long error_code)
+static void unexpected_machine_check(const struct cpu_user_regs *regs, long error_code)
 {
     console_force_unlock();
     printk("Unexpected Machine Check Exception\n");
@@ -88,7 +88,7 @@ void x86_mce_vector_register(x86_mce_vector_t hdlr)
 
 /* Call the installed machine check handler for this CPU setup. */
 
-void machine_check_vector(struct cpu_user_regs *regs, long error_code)
+void machine_check_vector(const struct cpu_user_regs *regs, long error_code)
 {
     _machine_check_vector(regs, error_code);
 }
@@ -424,7 +424,7 @@ static void mce_spin_unlock(spinlock_t *lk)
       spin_unlock(lk);
 }
 
-static enum mce_result mce_action(struct cpu_user_regs *regs,
+static enum mce_result mce_action(const struct cpu_user_regs *regs,
     mctelem_cookie_t mctc);
 
 /*
@@ -432,7 +432,7 @@ static enum mce_result mce_action(struct cpu_user_regs *regs,
  * -1: if system can't be recovered
  * 0: Continue to next step
  */
-static int mce_urgent_action(struct cpu_user_regs *regs,
+static int mce_urgent_action(const struct cpu_user_regs *regs,
                               mctelem_cookie_t mctc)
 {
     uint64_t gstatus;
@@ -459,7 +459,7 @@ static int mce_urgent_action(struct cpu_user_regs *regs,
 }
 
 /* Shared #MC handler. */
-void mcheck_cmn_handler(struct cpu_user_regs *regs, long error_code,
+void mcheck_cmn_handler(const struct cpu_user_regs *regs, long error_code,
     struct mca_banks *bankmask, struct mca_banks *clear_bank)
 {
     uint64_t gstatus;
@@ -1570,7 +1570,7 @@ void mc_panic(char *s)
  */
 
 /* Maybe called in MCE context, no lock, no printk */
-static enum mce_result mce_action(struct cpu_user_regs *regs,
+static enum mce_result mce_action(const struct cpu_user_regs *regs,
                       mctelem_cookie_t mctc)
 {
     struct mc_info *local_mi;

xen/arch/x86/cpu/mcheck/mce.h

@@ -62,12 +62,12 @@ void x86_mc_get_cpu_info(unsigned, uint32_t *, uint16_t *, uint16_t *,
 			 uint32_t *, uint32_t *, uint32_t *, uint32_t *);
 
 /* Register a handler for machine check exceptions. */
-typedef void (*x86_mce_vector_t)(struct cpu_user_regs *, long);
+typedef void (*x86_mce_vector_t)(const struct cpu_user_regs *, long);
 extern void x86_mce_vector_register(x86_mce_vector_t);
 
 /* Common generic MCE handler that implementations may nominate
  * via x86_mce_vector_register. */
-extern void mcheck_cmn_handler(struct cpu_user_regs *, long,
+extern void mcheck_cmn_handler(const struct cpu_user_regs *, long,
     struct mca_banks *, struct mca_banks *);
 
 /* Register a handler for judging whether mce is recoverable. */

xen/arch/x86/cpu/mcheck/mce_amd.c

@@ -242,7 +242,7 @@ amd_f10_handler(struct mc_info *mi, uint16_t bank, uint64_t status)
 }
 
 /* Common AMD Machine Check Handler for AMD K8 and higher */
-static void amd_cmn_machine_check(struct cpu_user_regs *regs, long error_code)
+static void amd_cmn_machine_check(const struct cpu_user_regs *regs, long error_code)
 {
     mcheck_cmn_handler(regs, error_code, mca_allbanks,
                        __get_cpu_var(mce_clear_banks));

xen/arch/x86/cpu/mcheck/mce_intel.c

@@ -258,7 +258,7 @@ static enum intel_mce_type intel_check_mce_type(uint64_t status)
 static void intel_memerr_dhandler(
              struct mca_binfo *binfo,
              enum mce_result *result,
-             struct cpu_user_regs *regs)
+             const struct cpu_user_regs *regs)
 {
     mce_printk(MCE_VERBOSE, "MCE: Enter UCR recovery action\n");
     mc_memerr_dhandler(binfo, result, regs);
@@ -285,7 +285,7 @@ static int intel_checkaddr(uint64_t status, uint64_t misc, int addrtype)
 static void intel_srar_dhandler(
              struct mca_binfo *binfo,
              enum mce_result *result,
-             struct cpu_user_regs *regs)
+             const struct cpu_user_regs *regs)
 {
     uint64_t status = binfo->mib->mc_status;
 
@@ -311,7 +311,7 @@ static int intel_srao_check(uint64_t status)
 static void intel_srao_dhandler(
              struct mca_binfo *binfo,
              enum mce_result *result,
-             struct cpu_user_regs *regs)
+             const struct cpu_user_regs *regs)
 {
     uint64_t status = binfo->mib->mc_status;
 
@@ -340,7 +340,7 @@ static int intel_default_check(uint64_t status)
 static void intel_default_mce_dhandler(
              struct mca_binfo *binfo,
              enum mce_result *result,
-             struct cpu_user_regs * regs)
+             const struct cpu_user_regs * regs)
 {
     uint64_t status = binfo->mib->mc_status;
     enum intel_mce_type type;
@@ -362,7 +362,7 @@ static const struct mca_error_handler intel_mce_dhandlers[] = {
 static void intel_default_mce_uhandler(
              struct mca_binfo *binfo,
              enum mce_result *result,
-             struct cpu_user_regs *regs)
+             const struct cpu_user_regs *regs)
 {
     uint64_t status = binfo->mib->mc_status;
     enum intel_mce_type type;
@@ -384,7 +384,7 @@ static const struct mca_error_handler intel_mce_uhandlers[] = {
     {intel_default_check, intel_default_mce_uhandler}
 };
 
-static void intel_machine_check(struct cpu_user_regs * regs, long error_code)
+static void intel_machine_check(const struct cpu_user_regs * regs, long error_code)
 {
     mcheck_cmn_handler(regs, error_code, mca_allbanks,
         __get_cpu_var(mce_clear_banks));

xen/arch/x86/cpu/mcheck/x86_mca.h

@@ -152,7 +152,7 @@ struct mca_error_handler
      */
     int (*owned_error)(uint64_t status);
     void (*recovery_handler)(struct mca_binfo *binfo,
-                    enum mce_result *result, struct cpu_user_regs *regs);
+                    enum mce_result *result, const struct cpu_user_regs *regs);
 };
 
 /* Global variables */

xen/arch/x86/nmi.c

@@ -432,7 +432,7 @@ int __init watchdog_setup(void)
     return 0;
 }
 
-void nmi_watchdog_tick(struct cpu_user_regs * regs)
+void nmi_watchdog_tick(const struct cpu_user_regs *regs)
 {
     unsigned int sum = this_cpu(nmi_timer_ticks);
 

xen/arch/x86/oprofile/nmi_int.c

@@ -82,7 +82,7 @@ void passive_domain_destroy(struct vcpu *v)
 		model->free_msr(v);
 }
 
-static int nmi_callback(struct cpu_user_regs *regs, int cpu)
+static int nmi_callback(const struct cpu_user_regs *regs, int cpu)
 {
 	int xen_mode, ovf;
 

xen/arch/x86/oprofile/op_model_athlon.c

@@ -237,7 +237,7 @@ static void athlon_setup_ctrs(struct op_msrs const * const msrs)
 }
 
 static inline void
-ibs_log_event(u64 data, struct cpu_user_regs * const regs, int mode)
+ibs_log_event(u64 data, struct cpu_user_regs const * const regs, int mode)
 {
 	struct vcpu *v = current;
 	u32 temp = 0;
@@ -250,7 +250,7 @@ ibs_log_event(u64 data, struct cpu_user_regs * const regs, int mode)
 	
 }
 
-static inline int handle_ibs(int mode, struct cpu_user_regs * const regs)
+static inline int handle_ibs(int mode, struct cpu_user_regs const * const regs)
 {
 	u64 val, ctl;
 	struct vcpu *v = current;
@@ -310,7 +310,7 @@ static inline int handle_ibs(int mode, struct cpu_user_regs * const regs)
 
 static int athlon_check_ctrs(unsigned int const cpu,
 			     struct op_msrs const * const msrs,
-			     struct cpu_user_regs * const regs)
+			     struct cpu_user_regs const * const regs)
 
 {
 	uint64_t msr_content;

xen/arch/x86/oprofile/op_model_p4.c

@@ -611,7 +611,7 @@ static void p4_setup_ctrs(struct op_msrs const * const msrs)
 
 static int p4_check_ctrs(unsigned int const cpu,
                          struct op_msrs const * const msrs,
-                         struct cpu_user_regs * const regs)
+                         struct cpu_user_regs const * const regs)
 {
 	unsigned long ctr, stag, real;
 	uint64_t msr_content;

xen/arch/x86/oprofile/op_model_ppro.c

@@ -126,7 +126,7 @@ static void ppro_setup_ctrs(struct op_msrs const * const msrs)
 
 static int ppro_check_ctrs(unsigned int const cpu,
                            struct op_msrs const * const msrs,
-                           struct cpu_user_regs * const regs)
+                           struct cpu_user_regs const * const regs)
 {
 	u64 val;
 	int i;

xen/arch/x86/oprofile/op_x86_model.h

@@ -33,7 +33,7 @@ struct op_x86_model_spec {
 	void (*setup_ctrs)(struct op_msrs const * const msrs);
 	int (*check_ctrs)(unsigned int const cpu, 
 			  struct op_msrs const * const msrs,
-			  struct cpu_user_regs * const regs);
+			  struct cpu_user_regs const * const regs);
 	void (*start)(struct op_msrs const * const msrs);
 	void (*stop)(struct op_msrs const * const msrs);
 	int (*is_arch_pmu_msr)(u64 msr_index, int *type, int *index);

xen/arch/x86/traps.c

@@ -114,7 +114,7 @@ boolean_param("ler", opt_ler);
 #define stack_words_per_line 4
 #define ESP_BEFORE_EXCEPTION(regs) ((unsigned long *)regs->rsp)
 
-static void show_guest_stack(struct vcpu *v, struct cpu_user_regs *regs)
+static void show_guest_stack(struct vcpu *v, const struct cpu_user_regs *regs)
 {
     int i;
     unsigned long *stack, addr;
@@ -290,7 +290,7 @@ static void show_trace(const struct cpu_user_regs *regs)
     printk("\n");
 }
 
-void show_stack(struct cpu_user_regs *regs)
+void show_stack(const struct cpu_user_regs *regs)
 {
     unsigned long *stack = ESP_BEFORE_EXCEPTION(regs), addr;
     int i;
@@ -349,7 +349,7 @@ void show_stack_overflow(unsigned int cpu, const struct cpu_user_regs *regs)
 #endif
 }
 
-void show_execution_state(struct cpu_user_regs *regs)
+void show_execution_state(const struct cpu_user_regs *regs)
 {
     show_registers(regs);
     show_stack(regs);
@@ -394,7 +394,7 @@ static const char *trapstr(unsigned int trapnr)
  * are disabled). In such situations we can't do much that is safe. We try to
  * print out some tracing and then we just spin.
  */
-void fatal_trap(int trapnr, struct cpu_user_regs *regs)
+void fatal_trap(int trapnr, const struct cpu_user_regs *regs)
 {
     static DEFINE_PER_CPU(char, depth);
 
@@ -1086,7 +1086,7 @@ void do_int3(struct cpu_user_regs *regs)
     do_guest_trap(TRAP_int3, regs, 0);
 }
 
-void do_machine_check(struct cpu_user_regs *regs)
+void do_machine_check(const struct cpu_user_regs *regs)
 {
     machine_check_vector(regs, regs->error_code);
 }
@@ -3240,7 +3240,7 @@ static void nmi_hwdom_report(unsigned int reason_idx)
     send_guest_trap(d, 0, TRAP_nmi);
 }
 
-static void pci_serr_error(struct cpu_user_regs *regs)
+static void pci_serr_error(const struct cpu_user_regs *regs)
 {
     outb((inb(0x61) & 0x0f) | 0x04, 0x61); /* clear-and-disable the PCI SERR error line. */
 
@@ -3260,7 +3260,7 @@ static void pci_serr_error(struct cpu_user_regs *regs)
     }
 }
 
-static void io_check_error(struct cpu_user_regs *regs)
+static void io_check_error(const struct cpu_user_regs *regs)
 {
     switch ( opt_nmi[0] )
     {
@@ -3279,7 +3279,7 @@ static void io_check_error(struct cpu_user_regs *regs)
     outb((inb(0x61) & 0x07) | 0x00, 0x61); /* enable IOCK */
 }
 
-static void unknown_nmi_error(struct cpu_user_regs *regs, unsigned char reason)
+static void unknown_nmi_error(const struct cpu_user_regs *regs, unsigned char reason)
 {
     switch ( opt_nmi[0] )
     {
@@ -3295,14 +3295,14 @@ static void unknown_nmi_error(struct cpu_user_regs *regs, unsigned char reason)
     }
 }
 
-static int dummy_nmi_callback(struct cpu_user_regs *regs, int cpu)
+static int dummy_nmi_callback(const struct cpu_user_regs *regs, int cpu)
 {
     return 0;
 }
  
 static nmi_callback_t nmi_callback = dummy_nmi_callback;
 
-void do_nmi(struct cpu_user_regs *regs)
+void do_nmi(const struct cpu_user_regs *regs)
 {
     unsigned int cpu = smp_processor_id();
     unsigned char reason;

xen/arch/x86/x86_64/compat/traps.c

@@ -3,7 +3,7 @@
 #include <compat/callback.h>
 #include <compat/arch-x86_32.h>
 
-void compat_show_guest_stack(struct vcpu *v, struct cpu_user_regs *regs,
+void compat_show_guest_stack(struct vcpu *v, const struct cpu_user_regs *regs,
                              int debug_stack_lines)
 {
     unsigned int i, *stack, addr, mask = STACK_SIZE;

xen/arch/x86/x86_64/traps.c

@@ -79,7 +79,7 @@ static void _show_registers(
            regs->gs, regs->ss, regs->cs);
 }
 
-void show_registers(struct cpu_user_regs *regs)
+void show_registers(const struct cpu_user_regs *regs)
 {
     struct cpu_user_regs fault_regs = *regs;
     unsigned long fault_crs[8];

xen/include/asm-x86/apic.h

@@ -206,7 +206,7 @@ extern void release_lapic_nmi(void);
 extern void self_nmi(void);
 extern void disable_timer_nmi_watchdog(void);
 extern void enable_timer_nmi_watchdog(void);
-extern void nmi_watchdog_tick (struct cpu_user_regs *regs);
+extern void nmi_watchdog_tick (const struct cpu_user_regs *regs);
 extern int APIC_init_uniprocessor (void);
 extern void disable_APIC_timer(void);
 extern void enable_APIC_timer(void);

xen/include/asm-x86/nmi.h

@@ -9,7 +9,7 @@ struct cpu_user_regs;
 /* Watchdog boolean from the command line */
 extern bool_t opt_watchdog;
  
-typedef int (*nmi_callback_t)(struct cpu_user_regs *regs, int cpu);
+typedef int (*nmi_callback_t)(const struct cpu_user_regs *regs, int cpu);
  
 /** 
  * set_nmi_callback

xen/include/asm-x86/processor.h

@@ -477,27 +477,32 @@ static always_inline void rep_nop(void)
 
 #define cpu_relax() rep_nop()
 
-void show_stack(struct cpu_user_regs *regs);
+void show_stack(const struct cpu_user_regs *regs);
 void show_stack_overflow(unsigned int cpu, const struct cpu_user_regs *regs);
-void show_registers(struct cpu_user_regs *regs);
-void show_execution_state(struct cpu_user_regs *regs);
+void show_registers(const struct cpu_user_regs *regs);
+void show_execution_state(const struct cpu_user_regs *regs);
 #define dump_execution_state() run_in_exception_handler(show_execution_state)
 void show_page_walk(unsigned long addr);
-void noreturn fatal_trap(int trapnr, struct cpu_user_regs *regs);
+void noreturn fatal_trap(int trapnr, const struct cpu_user_regs *regs);
 
-void compat_show_guest_stack(struct vcpu *, struct cpu_user_regs *, int lines);
+void compat_show_guest_stack(struct vcpu *v,
+                             const struct cpu_user_regs *regs, int lines);
 
 extern void mtrr_ap_init(void);
 extern void mtrr_bp_init(void);
 
 void mcheck_init(struct cpuinfo_x86 *c, bool_t bsp);
 
-#define DECLARE_TRAP_HANDLER(_name)                     \
-void _name(void);                            \
-void do_ ## _name(struct cpu_user_regs *regs)
+#define DECLARE_TRAP_HANDLER(_name)                    \
+    void _name(void);                                  \
+    void do_ ## _name(struct cpu_user_regs *regs)
+#define DECLARE_TRAP_HANDLER_CONST(_name)              \
+    void _name(void);                                  \
+    void do_ ## _name(const struct cpu_user_regs *regs)
+
 DECLARE_TRAP_HANDLER(divide_error);
 DECLARE_TRAP_HANDLER(debug);
-DECLARE_TRAP_HANDLER(nmi);
+DECLARE_TRAP_HANDLER_CONST(nmi);
 DECLARE_TRAP_HANDLER(int3);
 DECLARE_TRAP_HANDLER(overflow);
 DECLARE_TRAP_HANDLER(bounds);
@@ -512,8 +517,10 @@ DECLARE_TRAP_HANDLER(page_fault);
 DECLARE_TRAP_HANDLER(early_page_fault);
 DECLARE_TRAP_HANDLER(coprocessor_error);
 DECLARE_TRAP_HANDLER(simd_coprocessor_error);
-DECLARE_TRAP_HANDLER(machine_check);
+DECLARE_TRAP_HANDLER_CONST(machine_check);
 DECLARE_TRAP_HANDLER(alignment_check);
+
+#undef DECLARE_TRAP_HANDLER_CONST
 #undef DECLARE_TRAP_HANDLER
 
 void trap_nop(void);

xen/include/asm-x86/traps.h

@@ -28,7 +28,7 @@ struct softirq_trap {
 
 struct cpu_user_regs;
 
-extern void machine_check_vector(struct cpu_user_regs *regs, long error_code);
+extern void machine_check_vector(const struct cpu_user_regs *regs, long error_code);
 
 void async_exception_cleanup(struct vcpu *);