arm64: arch_timer: Disable the compat vdso for cores affected by ARM64_WORKAROUND_1418040

ARM64_WORKAROUND_1418040 requires that AArch32 EL0 accesses to
the virtual counter register are trapped and emulated by the kernel.
This makes the vdso pretty pointless, and in some cases livelock
prone.

Provide a workaround entry that limits the vdso to 64bit tasks.
Signed-off-by: Marc Zyngier <maz@kernel.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20200706163802.1836732-4-maz@kernel.orgSigned-off-by: Will Deacon <will@kernel.org>

drivers/clocksource/arm_arch_timer.c

@@ -480,6 +480,14 @@ static const struct arch_timer_erratum_workaround ool_workarounds[] = {
 		.set_next_event_virt = erratum_set_next_event_tval_virt,
 	},
 #endif
+#ifdef CONFIG_ARM64_ERRATUM_1418040
+	{
+		.match_type = ate_match_local_cap_id,
+		.id = (void *)ARM64_WORKAROUND_1418040,
+		.desc = "ARM erratum 1418040",
+		.disable_compat_vdso = true,
+	},
+#endif
 };
 
 typedef bool (*ate_match_fn_t)(const struct arch_timer_erratum_workaround *,