Re: [Xen-devel] [PATCH v2 05/10] x86/HVM/SVM: Add AVIC initialization code

[Suravee Suthikulpanit <Suravee.Suthikulpanit@xxxxxxx>]

Hi Andrew,

On 1/2/17 23:37, Andrew Cooper wrote:
> > +    ma = d->avic_phy_apic_id_table_mfn;
> > +    vmcb->avic_phy_apic_id = (ma << PAGE_SHIFT) & AVIC_HPA_MASK;
> > +    vmcb->avic_phy_apic_id |= AVIC_PHY_APIC_ID_MAX;
> Surely this should be some calculation derived from d->max_vcpus?
This is actually should be the value of highest physical APIC ID, since 
the documentations mentioned that this is the highest index into the 
physical APIC ID table.
I am checking with the HW folks to try to understand if there are any 
negative effects if we were to always set this to 0xFF.
However, I have also looking into setting/updating this in the following 
scenarios:
1. During svm_avic_init_vmcb(): We should be able to just have a 
for_each_vcpu() loop to iterate through all VMCBs and updating this 
field with the max physical APIC ID.
2. During avic_unaccel_trap_write()->avic_handle_apic_id_update():
This is more tricky since we would need to trap all VCPUs to update this 
field in all VMCBs to have the same value. What mechanism would you 
suggest to achieve this?
Thanks,
Suravee


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