Hi,
On 26/11/2019 21:13, Jeff Kubascik wrote:
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]
I am a bit confused, is it a new bug introduced by the change or
previously existing? If the latter, then I think this should be modified
in a separate patch.
Signed-off-by: Jeff Kubascik <jeff.kubas...@dornerworks.com>
---
Changes in v2:
- Update commit message to specify reference manual version and section
- Change physical timer cval to hold hardware value
I think this change should be explained in the commit message.
- 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);
I think you need to update the initialization of cval to avoid storing
ns. But CTNP_CVAL_EL0 is reset to a unknown value at reboot, so we
should not need to set a value at all as the guest would have to set it.
@@ -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));
cval may be smaller than boot_count. In that case, we will set the timer
to expire a very long time. This is not the expected behavior from the
guest.
Instead, we should either use 0 to create the timer or call
phys_timer_expired directly.
}
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));
I would prefer (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;
Cheers,
--
Julien Grall
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