On 6/17/2016 1:36 PM, Corneliu ZUZU wrote:
On 6/16/2016 7:49 PM, Julien Grall wrote:
Hello Corneliu,
On 16/06/16 15:13, Corneliu ZUZU wrote:
+ case MWS_TTBCR:
+ MWS_EMUL(TTBCR);
+ break;
+ default:
+ break;
+ }
+
+ w->status = MWS_NOWRITE;
+}
+
+static inline void vcpu_enter_adjust_traps(struct vcpu *v)
+{
+ register_t old_hcr, hcr;
+
+ hcr = (old_hcr = READ_SYSREG(HCR_EL2));
+
+ if ( unlikely(0 !=
v->domain->arch.monitor.write_ctrlreg_enabled) )
+ hcr |= HCR_TVM;
+ else
+ hcr &= ~HCR_TVM;
+
+ if ( unlikely(hcr != old_hcr) )
+ {
+ WRITE_SYSREG(hcr, HCR_EL2);
+ isb();
+ }
The HCR register is also updated in p2m_restore_state to set
HCR_EL2.RW. I would prefer to have a single place where HCR is updated.
Maybe we should store the HCR value per-domain?
Yes, that would be nice. Will look into that for v2.
Julien,
I was trying to implement having HCR stored in arch_domain or arch_vcpu
as suggested above and I'm a bit confused about the code in
p2m_restore_state.
I'm hoping you can provide some feedback on this matter. Here's the
current implementation of the function:
void p2m_restore_state(struct vcpu *n)
{
register_t hcr;
hcr = READ_SYSREG(HCR_EL2);
WRITE_SYSREG(hcr & ~HCR_VM, HCR_EL2);
isb();
p2m_load_VTTBR(n->domain);
isb();
if ( is_32bit_domain(n->domain) )
hcr &= ~HCR_RW;
else
hcr |= HCR_RW;
WRITE_SYSREG(n->arch.sctlr, SCTLR_EL1);
isb();
WRITE_SYSREG(hcr, HCR_EL2);
isb();
}
First of all, I see the HCR_VM bit being unset (=0) but I don't quite
understand why and even more peculiar is the fact that I couldn't find
any place where the bit is set (=1) again.
Secondly, why this order of operations? More specifically, why is
p2m_load_VTTBR done after the HCR_VM bit is unset and before the HCR_RW
bit is set/unset? Can't we write HCR only once here?
And finally, I see the function is called by construct_dom0. The code
there looks like:
/*
* The following loads use the domain's p2m and require current to
* be a vcpu of the domain, temporarily switch
*/
saved_current = current;
p2m_restore_state(v);
[...]
/* Now that we are done restore the original p2m and current. */
set_current(saved_current);
p2m_restore_state(saved_current);
I suppose the significant changes p2m_restore_state does for the code in
between ("[...]") is setting VTTBR & SCTLR which are used by translation
functions such as gvirt_to_maddr (which seems to use PAR_EL1).
What I don't grasp is what effect setting the VTTBR has if HCR.HCR_VM is
unset and left unset...
Thanks,
Corneliu.
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