arm64: pac: Optimize kernel entry/exit key installation code paths

The kernel does not use any keys besides IA so we don't need to
install IB/DA/DB/GA on kernel exit if we arrange to install them
on task switch instead, which we can expect to happen an order of
magnitude less often.

Furthermore we can avoid installing the user IA in the case where the
user task has IA disabled and just leave the kernel IA installed. This
also lets us avoid needing to install IA on kernel entry.

On an Apple M1 under a hypervisor, the overhead of kernel entry/exit
has been measured to be reduced by 15.6ns in the case where IA is
enabled, and 31.9ns in the case where IA is disabled.

Signed-off-by: Peter Collingbourne <pcc@google.com>
Link: https://linux-review.googlesource.com/id/Ieddf6b580d23c9e0bed45a822dabe72d2ffc9a8e
Link: https://lore.kernel.org/r/2d653d055f38f779937f2b92f8ddd5cf9e4af4f4.1616123271.git.pcc@google.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

2 files changed, 30 insertions, 26 deletions

diff --git a/arch/arm64/include/asm/asm_pointer_auth.h b/arch/arm64/include/asm/asm_pointer_auth.h
index 52dead2a8640..8ca2dc0661ee 100644
--- a/arch/arm64/include/asm/asm_pointer_auth.h
+++ b/arch/arm64/include/asm/asm_pointer_auth.h
@@ -13,30 +13,12 @@
  * so use the base value of ldp as thread.keys_user and offset as
  * thread.keys_user.ap*.
  */
-	.macro ptrauth_keys_install_user tsk, tmp1, tmp2, tmp3
+	.macro __ptrauth_keys_install_user tsk, tmp1, tmp2, tmp3
 	mov	\tmp1, #THREAD_KEYS_USER
 	add	\tmp1, \tsk, \tmp1
-alternative_if_not ARM64_HAS_ADDRESS_AUTH
-	b	.Laddr_auth_skip_\@
-alternative_else_nop_endif
 	ldp	\tmp2, \tmp3, [\tmp1, #PTRAUTH_USER_KEY_APIA]
 	msr_s	SYS_APIAKEYLO_EL1, \tmp2
 	msr_s	SYS_APIAKEYHI_EL1, \tmp3
-	ldp	\tmp2, \tmp3, [\tmp1, #PTRAUTH_USER_KEY_APIB]
-	msr_s	SYS_APIBKEYLO_EL1, \tmp2
-	msr_s	SYS_APIBKEYHI_EL1, \tmp3
-	ldp	\tmp2, \tmp3, [\tmp1, #PTRAUTH_USER_KEY_APDA]
-	msr_s	SYS_APDAKEYLO_EL1, \tmp2
-	msr_s	SYS_APDAKEYHI_EL1, \tmp3
-	ldp	\tmp2, \tmp3, [\tmp1, #PTRAUTH_USER_KEY_APDB]
-	msr_s	SYS_APDBKEYLO_EL1, \tmp2
-	msr_s	SYS_APDBKEYHI_EL1, \tmp3
-.Laddr_auth_skip_\@:
-alternative_if ARM64_HAS_GENERIC_AUTH
-	ldp	\tmp2, \tmp3, [\tmp1, #PTRAUTH_USER_KEY_APGA]
-	msr_s	SYS_APGAKEYLO_EL1, \tmp2
-	msr_s	SYS_APGAKEYHI_EL1, \tmp3
-alternative_else_nop_endif
 	.endm
 
 	.macro __ptrauth_keys_install_kernel_nosync tsk, tmp1, tmp2, tmp3
diff --git a/arch/arm64/include/asm/pointer_auth.h b/arch/arm64/include/asm/pointer_auth.h
index cefe7e9b6fa9..d50416be99be 100644
--- a/arch/arm64/include/asm/pointer_auth.h
+++ b/arch/arm64/include/asm/pointer_auth.h
@@ -35,6 +35,25 @@ struct ptrauth_keys_kernel {
 	struct ptrauth_key apia;
 };
 
+#define __ptrauth_key_install_nosync(k, v)			\
+do {								\
+	struct ptrauth_key __pki_v = (v);			\
+	write_sysreg_s(__pki_v.lo, SYS_ ## k ## KEYLO_EL1);	\
+	write_sysreg_s(__pki_v.hi, SYS_ ## k ## KEYHI_EL1);	\
+} while (0)
+
+static inline void ptrauth_keys_install_user(struct ptrauth_keys_user *keys)
+{
+	if (system_supports_address_auth()) {
+		__ptrauth_key_install_nosync(APIB, keys->apib);
+		__ptrauth_key_install_nosync(APDA, keys->apda);
+		__ptrauth_key_install_nosync(APDB, keys->apdb);
+	}
+
+	if (system_supports_generic_auth())
+		__ptrauth_key_install_nosync(APGA, keys->apga);
+}
+
 static inline void ptrauth_keys_init_user(struct ptrauth_keys_user *keys)
 {
 	if (system_supports_address_auth()) {
@@ -46,14 +65,9 @@ static inline void ptrauth_keys_init_user(struct ptrauth_keys_user *keys)
 
 	if (system_supports_generic_auth())
 		get_random_bytes(&keys->apga, sizeof(keys->apga));
-}
 
-#define __ptrauth_key_install_nosync(k, v)			\
-do {								\
-	struct ptrauth_key __pki_v = (v);			\
-	write_sysreg_s(__pki_v.lo, SYS_ ## k ## KEYLO_EL1);	\
-	write_sysreg_s(__pki_v.hi, SYS_ ## k ## KEYHI_EL1);	\
-} while (0)
+	ptrauth_keys_install_user(keys);
+}
 
 static __always_inline void ptrauth_keys_init_kernel(struct ptrauth_keys_kernel *keys)
 {
@@ -90,6 +104,9 @@ static __always_inline void ptrauth_enable(void)
 	isb();
 }
 
+#define ptrauth_suspend_exit()                                                 \
+	ptrauth_keys_install_user(&current->thread.keys_user)
+
 #define ptrauth_thread_init_user()                                             \
 	do {                                                                   \
 		ptrauth_keys_init_user(&current->thread.keys_user);            \
@@ -101,6 +118,9 @@ static __always_inline void ptrauth_enable(void)
 					   SCTLR_ELx_ENDA | SCTLR_ELx_ENDB);   \
 	} while (0)
 
+#define ptrauth_thread_switch_user(tsk)                                        \
+	ptrauth_keys_install_user(&(tsk)->thread.keys_user)
+
 #define ptrauth_thread_init_kernel(tsk)					\
 	ptrauth_keys_init_kernel(&(tsk)->thread.keys_kernel)
 #define ptrauth_thread_switch_kernel(tsk)				\
@@ -112,8 +132,10 @@ static __always_inline void ptrauth_enable(void)
 #define ptrauth_set_enabled_keys(tsk, keys, enabled)	(-EINVAL)
 #define ptrauth_get_enabled_keys(tsk)	(-EINVAL)
 #define ptrauth_strip_insn_pac(lr)	(lr)
+#define ptrauth_suspend_exit()
 #define ptrauth_thread_init_user()
 #define ptrauth_thread_init_kernel(tsk)
+#define ptrauth_thread_switch_user(tsk)
 #define ptrauth_thread_switch_kernel(tsk)
 #endif /* CONFIG_ARM64_PTR_AUTH */