arm64: generic timer: use virtual counter instead of physical at EL0

We want to use the virtual counter at EL0, as the physical counter
may not track the current clocksource for guests running under a
hypervisor.

This patch updates the vdso and generic timer driver to use the virtual
counter. The kernel EL2 entry code is also updated to ensure that the
virtual offset is initialised to zero.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

3 files changed, 7 insertions, 6 deletions

diff --git a/arch/arm64/include/asm/arm_generic.h b/arch/arm64/include/asm/arm_generic.h
index e4cec9d30f27..df2aeb82f74e 100644
--- a/arch/arm64/include/asm/arm_generic.h
+++ b/arch/arm64/include/asm/arm_generic.h
@@ -70,12 +70,12 @@ static inline void __cpuinit arch_counter_enable_user_access(void)
 {
         u32 cntkctl;
 
-        /* Disable user access to the timers and the virtual counter. */
+        /* Disable user access to the timers and the physical counter. */
         asm volatile("mrs       %0, cntkctl_el1" : "=r" (cntkctl));
-        cntkctl &= ~((3 << 8) | (1 << 1));
+        cntkctl &= ~((3 << 8) | (1 << 0));
 
-        /* Enable user access to the physical counter and frequency. */
-        cntkctl |= 1;
+        /* Enable user access to the virtual counter and frequency. */
+        cntkctl |= (1 << 1);
         asm volatile("msr       cntkctl_el1, %0" : : "r" (cntkctl));
 }
 
diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index a2f02b63eae9..90dec55b17a2 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -158,6 +158,7 @@ ENTRY(el2_setup)
         mrs     x0, cnthctl_el2
         orr     x0, x0, #3                      // Enable EL1 physical timers
         msr     cnthctl_el2, x0
+        msr     cntvoff_el2, xzr                // Clear virtual offset
 
         /* Populate ID registers. */
         mrs     x0, midr_el1
diff --git a/arch/arm64/kernel/vdso/gettimeofday.S b/arch/arm64/kernel/vdso/gettimeofday.S
index 6681f4032260..8bf658d974f9 100644
--- a/arch/arm64/kernel/vdso/gettimeofday.S
+++ b/arch/arm64/kernel/vdso/gettimeofday.S
@@ -220,9 +220,9 @@ ENTRY(__do_get_tspec)
         ldp     w11, w12, [vdso_data, #VDSO_CS_MULT]
         seqcnt_read w9
 
-        /* Read the physical counter. */
+        /* Read the virtual counter. */
         isb
-        mrs     x15, cntpct_el0
+        mrs     x15, cntvct_el0
 
         /* Calculate cycle delta and convert to ns. */
         sub     x10, x15, x10