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Re: [Xen-devel] [PATCH v3 1/2] xen/arm: remove physical timer offset
Hi,
On 17/01/2020 21:24, Jeff Kubascik wrote:
On 12/18/2019 9:20 AM, Julien Grall wrote:
Hi Jeff,
On 11/12/2019 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.
This also cleans up the physical timer implementation to better match
the virtual timer - both cval's now hold the hardware value.
Signed-off-by: Jeff Kubascik <jeff.kubascik@xxxxxxxxxxxxxxx>
---
xen/arch/arm/vtimer.c | 34 ++++++++++++++++++----------------
xen/include/asm-arm/domain.h | 3 ---
2 files changed, 18 insertions(+), 19 deletions(-)
diff --git a/xen/arch/arm/vtimer.c b/xen/arch/arm/vtimer.c
index e6aebdac9e..21b98ec20a 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);
@@ -108,7 +107,6 @@ int vcpu_vtimer_init(struct vcpu *v)
init_timer(&t->timer, phys_timer_expired, t, v->processor);
t->ctl = 0;
- t->cval = NOW();
t->irq = d0
? timer_get_irq(TIMER_PHYS_NONSECURE_PPI)
: GUEST_TIMER_PHYS_NS_PPI;
@@ -167,6 +165,7 @@ void virt_timer_restore(struct vcpu *v)
static bool vtimer_cntp_ctl(struct cpu_user_regs *regs, uint32_t *r, bool
read)
{
struct vcpu *v = current;
+ s_time_t expires;
if ( !ACCESS_ALLOWED(regs, EL0PTEN) )
return false;
@@ -184,8 +183,9 @@ 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);
+ expires = v->arch.phys_timer.cval > boot_count
+ ? ticks_to_ns(v->arch.phys_timer.cval - boot_count) : 0;
+ set_timer(&v->arch.phys_timer.timer, expires);
}
else
stop_timer(&v->arch.phys_timer.timer);
@@ -197,26 +197,27 @@ 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;
+ s_time_t expires;
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 + *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);
+ expires = v->arch.phys_timer.cval > boot_count
+ ? ticks_to_ns(v->arch.phys_timer.cval - boot_count) : 0;
You probably want a comment to explain why you set to 0 here.
This code is repeated in 3 places - it probably doesn't make sense to have 3
duplicate comments as well. I think it would fit well with your function
suggestion below.
If you don't write a new helper, then the comment *must* be duplicated
on every use. It is not pretty, but at least it avoids the reader to
wonder why this is done.
Similar, this should be explained in the commit message.
+ set_timer(&v->arch.phys_timer.timer, expires);
}
}
return true;
@@ -226,23 +227,24 @@ static bool vtimer_cntp_cval(struct cpu_user_regs *regs,
uint64_t *r,
bool read)
{
struct vcpu *v = current;
+ s_time_t expires;
if ( !ACCESS_ALLOWED(regs, EL0PTEN) )
return false;
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);
+ expires = v->arch.phys_timer.cval > boot_count
+ ? ticks_to_ns(v->arch.phys_timer.cval - boot_count) : 0;
Same here. But I am wondering whether we could factor this code in a
function. This would avoid code duplication and make the code simpler.
This can be done as a follow-up as we may want to backport the fix.
This is a great idea. However, I would consider this further scope creep for
this patch set - I think what is here is already a great improvement. I am
currently focused on wrapping up a project; unfortunately, this change would be
low on the priority list for me and I may not be able to get to it.
While the code factoring is a cleanup, I don't view the lack of comment
a great improvement. I quite like factoring, but I would not push it to
be done in this series.
However, I do care about code readability. It is not so hard to
duplicate comments and you could have easily handle it when respining
the series.
Cheers,
--
Julien Grall
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