powerpc: Introduce syscall exit arch functions

Add PowerPC-specific implementations of the generic syscall exit hooks
used by the generic entry/exit framework:

 - arch_exit_to_user_mode_work_prepare()
 - arch_exit_to_user_mode_work()

These helpers handle user state restoration when returning from the
kernel to userspace, including FPU/VMX/VSX state, transactional memory,
KUAP restore, and per-CPU accounting.

Additionally, move check_return_regs_valid() from interrupt.c to
interrupt.h so it can be shared by the new entry/exit logic.

No functional change is intended with this patch.

Signed-off-by: Mukesh Kumar Chaurasiya <mchauras@linux.ibm.com>
Tested-by: Samir M <samir@linux.ibm.com>
Tested-by: David Gow <davidgow@google.com>
Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Reviewed-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20260427122742.210074-5-mkchauras@gmail.com

diff --git a/arch/powerpc/include/asm/entry-common.h b/arch/powerpc/include/asm/entry-common.h
index 837a7e020e827a4ef5b67505acd487591905241c..ff0625e04778070b5edd6d47db82e0d278fa07f3 100644 (file)
--- a/arch/powerpc/include/asm/entry-common.h
+++ b/arch/powerpc/include/asm/entry-common.h
@@ -6,6 +6,7 @@
 #include <asm/cputime.h>
 #include <asm/interrupt.h>
 #include <asm/stacktrace.h>
+#include <asm/switch_to.h>
 #include <asm/tm.h>
 
 static __always_inline void booke_load_dbcr0(void)
@@ -123,4 +124,52 @@ static __always_inline void arch_enter_from_user_mode(struct pt_regs *regs)
 
 #define arch_enter_from_user_mode arch_enter_from_user_mode
 
+static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs,
+                                                 unsigned long ti_work)
+{
+       unsigned long mathflags;
+
+       if (IS_ENABLED(CONFIG_PPC_BOOK3S_64) && IS_ENABLED(CONFIG_PPC_FPU)) {
+               if (IS_ENABLED(CONFIG_PPC_TRANSACTIONAL_MEM) &&
+                   unlikely((ti_work & _TIF_RESTORE_TM))) {
+                       restore_tm_state(regs);
+               } else {
+                       mathflags = MSR_FP;
+
+                       if (cpu_has_feature(CPU_FTR_VSX))
+                               mathflags |= MSR_VEC | MSR_VSX;
+                       else if (cpu_has_feature(CPU_FTR_ALTIVEC))
+                               mathflags |= MSR_VEC;
+
+                       /*
+                        * If userspace MSR has all available FP bits set,
+                        * then they are live and no need to restore. If not,
+                        * it means the regs were given up and restore_math
+                        * may decide to restore them (to avoid taking an FP
+                        * fault).
+                        */
+                       if ((regs->msr & mathflags) != mathflags)
+                               restore_math(regs);
+               }
+       }
+
+       check_return_regs_valid(regs);
+#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
+       local_paca->tm_scratch = regs->msr;
+#endif
+       /* Restore user access locks last */
+       kuap_user_restore(regs);
+}
+
+#define arch_exit_to_user_mode_prepare arch_exit_to_user_mode_prepare
+
+static __always_inline void arch_exit_to_user_mode(void)
+{
+       booke_load_dbcr0();
+
+       account_cpu_user_exit();
+}
+
+#define arch_exit_to_user_mode arch_exit_to_user_mode
+
 #endif /* _ASM_PPC_ENTRY_COMMON_H */