[Xen-devel] [PATCH v2] xen/arm: remove physical timer offset

[Jeff Kubascik <jeff.kubascik@xxxxxxxxxxxxxxx>]

The physical timer traps apply an offset so that time starts at 0 for
the guest. However, this offset is not currently applied to the physical
counter. Per the ARMv8 Reference Manual (ARM DDI 0487E.a), section
D11.2.4 Timers, the "Offset" between the counter and timer should be
zero for a physical timer. This removes the offset to make the timer and
counter consistent.

Furthermore, 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>
---
Changes in v2:
- Update commit message to specify reference manual version and section
- Change physical timer cval to hold hardware value
- Make sure to sign extend TimerValue on writes. This was done by first
  casting the r pointer to (int32_t *), dereferencing it, then casting
  to uint64_t. Please let me know if there is a more correct way to do
  this
---
 xen/arch/arm/vtimer.c        | 21 +++++++++------------
 xen/include/asm-arm/domain.h |  3 ---
 2 files changed, 9 insertions(+), 15 deletions(-)

diff --git a/xen/arch/arm/vtimer.c b/xen/arch/arm/vtimer.c
index e6aebdac9e..eb12a08acf 100644
--- a/xen/arch/arm/vtimer.c
+++ b/xen/arch/arm/vtimer.c
@@ -62,7 +62,6 @@ static void virt_timer_expired(void *data)
 
 int domain_vtimer_init(struct domain *d, struct xen_arch_domainconfig *config)
 {
-    d->arch.phys_timer_base.offset = NOW();
     d->arch.virt_timer_base.offset = READ_SYSREG64(CNTPCT_EL0);
     d->time_offset_seconds = ticks_to_ns(d->arch.virt_timer_base.offset - 
boot_count);
     do_div(d->time_offset_seconds, 1000000000);
@@ -185,7 +184,7 @@ static bool vtimer_cntp_ctl(struct cpu_user_regs *regs, 
uint32_t *r, bool read)
         if ( v->arch.phys_timer.ctl & CNTx_CTL_ENABLE )
         {
             set_timer(&v->arch.phys_timer.timer,
-                      v->arch.phys_timer.cval + 
v->domain->arch.phys_timer_base.offset);
+                      ticks_to_ns(v->arch.phys_timer.cval - boot_count));
         }
         else
             stop_timer(&v->arch.phys_timer.timer);
@@ -197,26 +196,25 @@ static bool vtimer_cntp_tval(struct cpu_user_regs *regs, 
uint32_t *r,
                              bool read)
 {
     struct vcpu *v = current;
-    s_time_t now;
+    uint64_t cntpct;
 
     if ( !ACCESS_ALLOWED(regs, EL0PTEN) )
         return false;
 
-    now = NOW() - v->domain->arch.phys_timer_base.offset;
+    cntpct = get_cycles();
 
     if ( read )
     {
-        *r = (uint32_t)(ns_to_ticks(v->arch.phys_timer.cval - now) & 
0xffffffffull);
+        *r = (uint32_t)((v->arch.phys_timer.cval - cntpct) & 0xffffffffull);
     }
     else
     {
-        v->arch.phys_timer.cval = now + ticks_to_ns(*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;
             set_timer(&v->arch.phys_timer.timer,
-                      v->arch.phys_timer.cval +
-                      v->domain->arch.phys_timer_base.offset);
+                      ticks_to_ns(v->arch.phys_timer.cval - boot_count));
         }
     }
     return true;
@@ -232,17 +230,16 @@ static bool vtimer_cntp_cval(struct cpu_user_regs *regs, 
uint64_t *r,
 
     if ( read )
     {
-        *r = ns_to_ticks(v->arch.phys_timer.cval);
+        *r = v->arch.phys_timer.cval;
     }
     else
     {
-        v->arch.phys_timer.cval = ticks_to_ns(*r);
+        v->arch.phys_timer.cval = *r;
         if ( v->arch.phys_timer.ctl & CNTx_CTL_ENABLE )
         {
             v->arch.phys_timer.ctl &= ~CNTx_CTL_PENDING;
             set_timer(&v->arch.phys_timer.timer,
-                      v->arch.phys_timer.cval +
-                      v->domain->arch.phys_timer_base.offset);
+                      ticks_to_ns(v->arch.phys_timer.cval - boot_count));
         }
     }
     return true;
diff --git a/xen/include/asm-arm/domain.h b/xen/include/asm-arm/domain.h
index 86ebdd2bcf..16a7150a95 100644
--- a/xen/include/asm-arm/domain.h
+++ b/xen/include/asm-arm/domain.h
@@ -65,9 +65,6 @@ struct arch_domain
         RELMEM_done,
     } relmem;
 
-    struct {
-        uint64_t offset;
-    } phys_timer_base;
     struct {
         uint64_t offset;
     } virt_timer_base;
-- 
2.17.1


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