arm64: arch_timer: Enable CNTVCT_EL0 trap if workaround is enabled

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.

Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

1 files changed, 32 insertions, 13 deletions

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index 5c114da0ed71..f8adea258cf0 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);
 
@@ -383,6 +384,17 @@ 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,
@@ -443,11 +455,19 @@ 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,
@@ -660,15 +680,23 @@ static void arch_counter_set_user_access(void)
 {
         u32 cntkctl = arch_timer_get_cntkctl();
 
-        /* Disable user access to the timers and the physical counter */
+        /* Disable user access to the timers and both counters */
         /* Also disable virtual event stream */
         cntkctl &= ~(ARCH_TIMER_USR_PT_ACCESS_EN
                         | ARCH_TIMER_USR_VT_ACCESS_EN
+                        | ARCH_TIMER_USR_VCT_ACCESS_EN
                         | 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);
 }
@@ -791,16 +819,7 @@ 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;
         }