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

[Marc Zyngier]

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