[PATCH v2 4/4] arm64: Rework ARM_ERRATUM_1414080 handling

From: Marc Zyngier
Date: Mon Jul 06 2020 - 12:38:27 EST


The current handling of erratum 1414080 has the side effect that
cntkctl_el1 can get changed for both 32 and 64bit tasks.

This isn't a problem so far, but if we ever need to mitigate another
of these errata on the 64bit side, we'd better keep the messing with
cntkctl_el1 local to 32bit tasks.

For that, make sure that on entering the kernel from a 32bit tasks,
userspace access to cntvct gets enabled, and disabled returning to
userspace, while it never gets changed for 64bit tasks.

Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
---
arch/arm64/kernel/entry.S | 40 +++++++++++++++++++++++----------------
1 file changed, 24 insertions(+), 16 deletions(-)

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 5304d193c79d..8f51f3273bc7 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -167,6 +167,19 @@ alternative_cb_end
stp x28, x29, [sp, #16 * 14]

.if \el == 0
+ .if \regsize == 32
+ // If we come back from a 32bit task on a system affected by
+ // 1418040, let's reenable userspace access to the virtual counter.
+#ifdef CONFIG_ARM64_ERRATUM_1418040
+alternative_if_not ARM64_WORKAROUND_1418040
+ b .L__entry_skip_wa_1418040\@
+alternative_else_nop_endif
+ mrs x0, cntkctl_el1
+ orr x0, x0, #2 // ARCH_TIMER_USR_VCT_ACCESS_EN
+ msr cntkctl_el1, x0
+.L__entry_skip_wa_1418040\@:
+#endif
+ .endif
clear_gp_regs
mrs x21, sp_el0
ldr_this_cpu tsk, __entry_task, x20
@@ -318,7 +331,17 @@ alternative_else_nop_endif
ldr x23, [sp, #S_SP] // load return stack pointer
msr sp_el0, x23
tst x22, #PSR_MODE32_BIT // native task?
- b.eq 3f
+ b.eq 4f
+
+#ifdef CONFIG_ARM64_ERRATUM_1418040
+alternative_if_not ARM64_WORKAROUND_1418040
+ b 3f
+alternative_else_nop_endif
+ mrs x1, cntkctl_el1
+ bic x1, x1, #2 // ARCH_TIMER_USR_VCT_ACCESS_EN
+ msr cntkctl_el1, x1
+3:
+#endif

#ifdef CONFIG_ARM64_ERRATUM_845719
alternative_if ARM64_WORKAROUND_845719
@@ -330,22 +353,7 @@ alternative_if ARM64_WORKAROUND_845719
#endif
alternative_else_nop_endif
#endif
-3:
-#ifdef CONFIG_ARM64_ERRATUM_1418040
-alternative_if_not ARM64_WORKAROUND_1418040
- b 4f
-alternative_else_nop_endif
- /*
- * if (x22.mode32 == cntkctl_el1.el0vcten)
- * cntkctl_el1.el0vcten = ~cntkctl_el1.el0vcten
- */
- mrs x1, cntkctl_el1
- eon x0, x1, x22, lsr #3
- tbz x0, #1, 4f
- eor x1, x1, #2 // ARCH_TIMER_USR_VCT_ACCESS_EN
- msr cntkctl_el1, x1
4:
-#endif
scs_save tsk, x0

/* No kernel C function calls after this as user keys are set. */
--
2.27.0