Re: [PATCH v5 4/7] kvm, mem-hotplug: Reload L1' apic access page on migration in vcpu_enter_guest().

Paolo Bonzini
2014-09-11T10:47:33Z

Il 11/09/2014 12:12, Gleb Natapov ha scritto:
> On Thu, Sep 11, 2014 at 11:21:49AM +0200, Paolo Bonzini wrote:
>> Il 11/09/2014 07:38, Tang Chen ha scritto:
>>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>>> index 63c4c3e..da6d55d 100644
>>> --- a/arch/x86/kvm/vmx.c
>>> +++ b/arch/x86/kvm/vmx.c
>>> @@ -7093,6 +7093,11 @@ static void vmx_set_virtual_x2apic_mode(struct kvm_vcpu *vcpu, bool set)
>>> vmx_set_msr_bitmap(vcpu);
>>> }
>>>
>>> +static void vmx_set_apic_access_page_addr(struct kvm *kvm, hpa_t hpa)
>>> +{
>>> + vmcs_write64(APIC_ACCESS_ADDR, hpa);
>>
>> This has to be guarded by "if (!is_guest_mode(vcpu))".
>>
> We do need to write it if L1 and L2 share APIC_ACCESS_ADDR and skip
> it otherwise, no?

Yes, but this would be handled by patch 6:

} else if (vm_need_virtualize_apic_accesses(vmx->vcpu.kvm)) {
+ struct page *page = gfn_to_page(vmx->vcpu.kvm,
+ APIC_DEFAULT_PHYS_BASE >> PAGE_SHIFT);
exec_control |=
SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES;
- vmcs_write64(APIC_ACCESS_ADDR,
- page_to_phys(vcpu->kvm->arch.apic_access_page));
+ vmcs_write64(APIC_ACCESS_ADDR, page_to_phys(page));
+ /*
+ * Do not pin apic access page in memory so that memory
+ * hotplug process is able to migrate it.
+ */
+ put_page(page);
}

However, this is also useless code duplication because the above snippet could
reuse vcpu_reload_apic_access_page too.

So I think you cannot do the is_guest_mode check in
kvm_vcpu_reload_apic_access_page and also not in
vmx_reload_apic_access_page. But you could do something like

kvm_vcpu_reload_apic_access_page(...)
{
...
kvm_x86_ops->reload_apic_access_page(...);
}
EXPORT_SYMBOL_GPL(kvm_vcpu_reload_apic_access_page);

/* used in vcpu_enter_guest only */
vcpu_reload_apic_access_page(...)
{
if (!is_guest_mode(vcpu))
kvm_vcpu_reload_apic_access_page(...)
}

Paolo