arm64: mte: avoid TFSRE0_EL1 related operations unless in async mode
There is no reason to touch TFSRE0_EL1 nor issue a DSB unless our task
is in asynchronous mode. Since these operations (especially the DSB) may
be expensive on certain microarchitectures, only perform them if
necessary.
Furthermore, stop clearing TFSRE0_EL1 on entry because it will be
cleared on exit and it is not necessary to have any particular value in
TFSRE0_EL1 between entry and exit.
Signed-off-by: Peter Collingbourne <pcc@google.com>
Link: https://linux-review.googlesource.com/id/Ib353a63e3d0abc2b0b008e96aa2d9692cfc1b815
Link: https://lore.kernel.org/r/20210709023532.2133673-1-pcc@google.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 863d44f..5cf1601 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -133,29 +133,37 @@
.endm
/* Check for MTE asynchronous tag check faults */
- .macro check_mte_async_tcf, tmp, ti_flags
+ .macro check_mte_async_tcf, tmp, ti_flags, thread_sctlr
#ifdef CONFIG_ARM64_MTE
.arch_extension lse
alternative_if_not ARM64_MTE
b 1f
alternative_else_nop_endif
+ /*
+ * Asynchronous tag check faults are only possible in ASYNC (2) or
+ * ASYM (3) modes. In each of these modes bit 1 of SCTLR_EL1.TCF0 is
+ * set, so skip the check if it is unset.
+ */
+ tbz \thread_sctlr, #(SCTLR_EL1_TCF0_SHIFT + 1), 1f
mrs_s \tmp, SYS_TFSRE0_EL1
tbz \tmp, #SYS_TFSR_EL1_TF0_SHIFT, 1f
/* Asynchronous TCF occurred for TTBR0 access, set the TI flag */
mov \tmp, #_TIF_MTE_ASYNC_FAULT
add \ti_flags, tsk, #TSK_TI_FLAGS
stset \tmp, [\ti_flags]
- msr_s SYS_TFSRE0_EL1, xzr
1:
#endif
.endm
/* Clear the MTE asynchronous tag check faults */
- .macro clear_mte_async_tcf
+ .macro clear_mte_async_tcf thread_sctlr
#ifdef CONFIG_ARM64_MTE
alternative_if ARM64_MTE
+ /* See comment in check_mte_async_tcf above. */
+ tbz \thread_sctlr, #(SCTLR_EL1_TCF0_SHIFT + 1), 1f
dsb ish
msr_s SYS_TFSRE0_EL1, xzr
+1:
alternative_else_nop_endif
#endif
.endm
@@ -231,8 +239,8 @@
disable_step_tsk x19, x20
/* Check for asynchronous tag check faults in user space */
- check_mte_async_tcf x22, x23
- apply_ssbd 1, x22, x23
+ ldr x0, [tsk, THREAD_SCTLR_USER]
+ check_mte_async_tcf x22, x23, x0
#ifdef CONFIG_ARM64_PTR_AUTH
alternative_if ARM64_HAS_ADDRESS_AUTH
@@ -245,7 +253,6 @@
* was disabled on kernel exit then we would have left the kernel IA
* installed so there is no need to install it again.
*/
- ldr x0, [tsk, THREAD_SCTLR_USER]
tbz x0, SCTLR_ELx_ENIA_SHIFT, 1f
__ptrauth_keys_install_kernel_nosync tsk, x20, x22, x23
b 2f
@@ -258,6 +265,8 @@
alternative_else_nop_endif
#endif
+ apply_ssbd 1, x22, x23
+
mte_set_kernel_gcr x22, x23
scs_load tsk
@@ -362,6 +371,10 @@
3:
scs_save tsk
+ /* Ignore asynchronous tag check faults in the uaccess routines */
+ ldr x0, [tsk, THREAD_SCTLR_USER]
+ clear_mte_async_tcf x0
+
#ifdef CONFIG_ARM64_PTR_AUTH
alternative_if ARM64_HAS_ADDRESS_AUTH
/*
@@ -371,7 +384,6 @@
*
* No kernel C function calls after this.
*/
- ldr x0, [tsk, THREAD_SCTLR_USER]
tbz x0, SCTLR_ELx_ENIA_SHIFT, 1f
__ptrauth_keys_install_user tsk, x0, x1, x2
b 2f
@@ -599,8 +611,6 @@
cbnz x2, work_pending
finish_ret_to_user:
user_enter_irqoff
- /* Ignore asynchronous tag check faults in the uaccess routines */
- clear_mte_async_tcf
enable_step_tsk x19, x2
#ifdef CONFIG_GCC_PLUGIN_STACKLEAK
bl stackleak_erase
