Hi Jiami
Title: s/caclulations/calculations/
However, I think the title should mention the overflow rather than the
extra calculations. The former is more important the latter.
On 27/06/2022 03:58, Jiamei Xie wrote:
virt_vtimer_save is calculating the new time for the vtimer in:
"v->arch.virt_timer.cval + v->domain->arch.virt_timer_base.offset
- boot_count".
In this formula, "cval + offset" might cause uint64_t overflow.
Changing it to "v->domain->arch.virt_timer_base.offset - boot_count +
v->arch.virt_timer.cval" can reduce the possibility of overflow
This read strange to me. We want to remove the overflow completely not
reducing it. The overflow is completely removed by converting the
"offset - bount_count" to ns upfront.
AFAICT, the commit message doesn't explain that.
, and
"arch.virt_timer_base.offset - boot_count" will be always the same,
which has been caculated in domain_vtimer_init. Introduce a new field
vtimer_offset.nanoseconds to store this value for arm in struct
arch_domain, so we can use it directly and extra caclulations can be
avoided.
This patch is enlightened from [1].
Signed-off-by: Jiamei Xie <jiamei....@arm.com>
[1] https://www.mail-archive.com/xen-devel@lists.xenproject.org/msg123139.htm
This link doesn't work. But I would personally remove it from the commit
message (or add ---) because it doesn't bring value (this patch looks
like a v2 to me).
---
xen/arch/arm/include/asm/domain.h | 4 ++++
xen/arch/arm/vtimer.c | 6 ++++--
2 files changed, 8 insertions(+), 2 deletions(-)
diff --git a/xen/arch/arm/include/asm/domain.h
b/xen/arch/arm/include/asm/domain.h
index ed63c2b6f9..94fe5b6444 100644
--- a/xen/arch/arm/include/asm/domain.h
+++ b/xen/arch/arm/include/asm/domain.h
@@ -73,6 +73,10 @@ struct arch_domain
uint64_t offset;
} virt_timer_base;
+ struct {
+ int64_t nanoseconds;
This should be s_time_t to match the argument of set_timer() and return
of ticks_to_ns().
+ } vtimer_offset;
Why are you adding a new structure rather than re-using virt_timer_base?
+
struct vgic_dist vgic;
struct vuart {
diff --git a/xen/arch/arm/vtimer.c b/xen/arch/arm/vtimer.c
index 6b78fea77d..54161e5fea 100644
--- a/xen/arch/arm/vtimer.c
+++ b/xen/arch/arm/vtimer.c
@@ -64,6 +64,7 @@ int domain_vtimer_init(struct domain *d, struct
xen_arch_domainconfig *config)
{
d->arch.virt_timer_base.offset = get_cycles();
d->time_offset.seconds = ticks_to_ns(d->arch.virt_timer_base.offset -
boot_count);
+ d->arch.vtimer_offset.nanoseconds = d->time_offset.seconds;
Hmmm... I find odd to assign a field "nanoseconds" to "seconds". I would
suggest to re-order so you first set nanoseconds and then set seconds.
This will make more obvious that this is not a mistake and "seconds"
will be closer to the do_div() below.
do_div(d->time_offset.seconds, 1000000000);
config->clock_frequency = timer_dt_clock_frequency;
@@ -144,8 +145,9 @@ void virt_timer_save(struct vcpu *v)
if ( (v->arch.virt_timer.ctl & CNTx_CTL_ENABLE) &&
!(v->arch.virt_timer.ctl & CNTx_CTL_MASK))
{
- set_timer(&v->arch.virt_timer.timer,
ticks_to_ns(v->arch.virt_timer.cval +
- v->domain->arch.virt_timer_base.offset - boot_count));
+ set_timer(&v->arch.virt_timer.timer,
+ v->domain->arch.vtimer_offset.nanoseconds +
+ ticks_to_ns(v->arch.virt_timer.cval));
}
}
Cheers,
--
Julien Grall
