Hi Wei,
On 03/31/2017 03:10 AM, Wei Chen wrote:
Hi Julien and Stefano,
On 2017/3/31 6:03, Stefano Stabellini wrote:
On Thu, 30 Mar 2017, Julien Grall wrote:
Hi Wei,
On 30/03/17 10:13, Wei Chen wrote:
diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
index de59e5f..8af223e 100644
--- a/xen/arch/arm/domain_build.c
+++ b/xen/arch/arm/domain_build.c
@@ -2171,6 +2171,13 @@ int construct_dom0(struct domain *d)
return rc;
/*
+ * The HCR_EL2 will temporarily switch to dom0's HCR_EL2 value
+ * by p2m_restore_state. We have to save HCR_EL2 to idle vCPU's
+ * context for restoring it in later.
+ */
+ current->arch.hcr_el2 = READ_SYSREG(HCR_EL2);
I don't understand why we care here. idle vCPU will never restore HCR_EL2 nor
return from the hypervisor.
I don't understand this either
Yes, idle vCPU will never return from hypervisor. But in construct_dom0,
it has one chance to restore HCR_EL2.
In in construct_dom0 we will call p2m_restore_state twice.
saved_current = current;
p2m_restore_state(v); --->> This is dom0's vCPU0
[...]
set_current(saved_current);
p2m_restore_state(saved_current); --->> this is idle vCPU0
In p2m_restore_state, we will write vcpu->arch.hcr_el2 to HCR_EL2. in
this case, we will write an unknown value to HCR_EL2. Even though this
would not cause any problem from my current testing. But from code
scope, I think it would be a drawback.
The p2m_restore_state will do nothing for idle vCPU (see check at the
beginning of the function). So there are no issue.
Cheers,
--
Julien Grall
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