[Xen-devel] [PATCH v3 2/2] xen/arm: sign extend writes to TimerValue

[Jeff Kubascik <jeff.kubascik@xxxxxxxxxxxxxxx>]

Per the ARMv8 Reference Manual (ARM DDI 0487E.a), section D11.2.4
specifies that the values in the TimerValue view of the timers are
signed in standard two's complement form. When writing to the TimerValue
register, it should be signed extended as described by the equation

   CompareValue = (Counter[63:0] + SignExtend(TimerValue))[63:0]

Signed-off-by: Jeff Kubascik <jeff.kubascik@xxxxxxxxxxxxxxx>
---
 xen/arch/arm/vtimer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/arch/arm/vtimer.c b/xen/arch/arm/vtimer.c
index 21b98ec20a..872181d9b6 100644
--- a/xen/arch/arm/vtimer.c
+++ b/xen/arch/arm/vtimer.c
@@ -211,7 +211,7 @@ static bool vtimer_cntp_tval(struct cpu_user_regs *regs, 
uint32_t *r,
     }
     else
     {
-        v->arch.phys_timer.cval = cntpct + *r;
+        v->arch.phys_timer.cval = cntpct + (uint64_t)(int32_t)*r;
         if ( v->arch.phys_timer.ctl & CNTx_CTL_ENABLE )
         {
             v->arch.phys_timer.ctl &= ~CNTx_CTL_PENDING;
-- 
2.17.1


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel