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Subject[PATCH v2 15/18] arm64: arch_timer: Enable CNTVCT_EL0 trap if workaround is enabled
Date
Userspace being allowed to use read CNTVCT_EL0 anytime (and not
only in the VDSO), we need to enable trapping whenever a cntvct
workaround is enabled on a given CPU.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
drivers/clocksource/arm_arch_timer.c | 42 +++++++++++++++++++++++++-----------
1 file changed, 30 insertions(+), 12 deletions(-)

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index 70eb42bd6784..eccff0fedf2c 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -83,6 +83,7 @@ static enum ppi_nr arch_timer_uses_ppi = VIRT_PPI;
static bool arch_timer_c3stop;
static bool arch_timer_mem_use_virtual;
static bool arch_counter_suspend_stop;
+static bool vdso_default = true;

static bool evtstrm_enable = IS_ENABLED(CONFIG_ARM_ARCH_TIMER_EVTSTREAM);

@@ -390,6 +391,17 @@ void arch_timer_enable_workaround(const struct arch_timer_erratum_workaround *wa
}

static_branch_enable(&arch_timer_read_ool_enabled);
+
+ /*
+ * Don't use the vdso fastpath if errata require using the
+ * out-of-line counter accessor. We may change our mind pretty
+ * late in the game (with a per-CPU erratum, for example), so
+ * change both the default value and the vdso itself.
+ */
+ if (wa->read_cntvct_el0) {
+ clocksource_counter.archdata.vdso_direct = false;
+ vdso_default = false;
+ }
}

static void arch_timer_check_ool_workaround(enum arch_timer_erratum_match_type type,
@@ -450,11 +462,19 @@ static void arch_timer_check_ool_workaround(enum arch_timer_erratum_match_type t
__val; \
})

+static bool arch_timer_this_cpu_has_cntvct_wa(void)
+{
+ const struct arch_timer_erratum_workaround *wa;
+
+ wa = __this_cpu_read(timer_unstable_counter_workaround);
+ return wa && wa->read_cntvct_el0;
+}
#else
#define arch_timer_check_ool_workaround(t,a) do { } while(0)
#define erratum_set_next_event_tval_virt(...) ({BUG(); 0;})
#define erratum_set_next_event_tval_phys(...) ({BUG(); 0;})
#define erratum_handler(fn, r, ...) ({false;})
+#define arch_timer_this_cpu_has_cntvct_wa() ({false;})
#endif /* CONFIG_ARM_ARCH_TIMER_OOL_WORKAROUND */

static __always_inline irqreturn_t timer_handler(const int access,
@@ -674,8 +694,15 @@ static void arch_counter_set_user_access(void)
| ARCH_TIMER_VIRT_EVT_EN
| ARCH_TIMER_USR_PCT_ACCESS_EN);

- /* Enable user access to the virtual counter */
- cntkctl |= ARCH_TIMER_USR_VCT_ACCESS_EN;
+ /*
+ * Enable user access to the virtual counter if it doesn't
+ * need to be workaround. The vdso may have been already
+ * disabled though.
+ */
+ if (arch_timer_this_cpu_has_cntvct_wa())
+ pr_info("CPU%d: Trapping CNTVCT access\n", smp_processor_id());
+ else
+ cntkctl |= ARCH_TIMER_USR_VCT_ACCESS_EN;

arch_timer_set_cntkctl(cntkctl);
}
@@ -798,16 +825,7 @@ static void __init arch_counter_register(unsigned type)
else
arch_timer_read_counter = arch_counter_get_cntpct;

- clocksource_counter.archdata.vdso_direct = true;
-
-#ifdef CONFIG_ARM_ARCH_TIMER_OOL_WORKAROUND
- /*
- * Don't use the vdso fastpath if errata require using
- * the out-of-line counter accessor.
- */
- if (static_branch_unlikely(&arch_timer_read_ool_enabled))
- clocksource_counter.archdata.vdso_direct = false;
-#endif
+ clocksource_counter.archdata.vdso_direct = vdso_default;
} else {
arch_timer_read_counter = arch_counter_get_cntvct_mem;
}
--
2.11.0
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