Re: [Qemu-devel] [QEMU PATCH v3 7/9] KVM: i386: Add support for save and restore nested state

[Dr. David Alan Gilbert]

* Liran Alon (address@hidden) wrote:
> 
> > On 18 Jun 2019, at 12:03, Dr. David Alan Gilbert <address@hidden> wrote:
> > 
> > * Liran Alon (address@hidden) wrote:
> >> 
> >> +static const VMStateDescription vmstate_vmx_vmcs12 = {
> >> +  .name = "cpu/kvm_nested_state/vmx/vmcs12",
> >> +  .version_id = 1,
> >> +  .minimum_version_id = 1,
> >> +  .needed = vmx_vmcs12_needed,
> >> +  .fields = (VMStateField[]) {
> >> +      VMSTATE_UINT8_ARRAY(data.vmx[0].vmcs12,
> >> +                          struct kvm_nested_state, 0x1000),
> > 
> > Where did that magic 0x1000 come from?
> 
> Currently, KVM folks (including myself), haven’t decided yet to expose vmcs12 
> struct layout to userspace but instead to still leave it opaque.
> The formal size of this size is VMCS12_SIZE (defined in kernel as 0x1000). I 
> was wondering if we wish to expose VMCS12_SIZE constant to userspace or not.
> So currently I defined these __u8 arrays as 0x1000. But in case Paolo agrees 
> to expose VMCS12_SIZE, we can use that instead.

Well if it's not defined it's bound to change at some state!
Also, do we need to clear it before we get it from the kernel - e.g.
is the kernel guaranteed to give us 0x1000 ?

Dave

> -Liran
> 
> > --
> > Dr. David Alan Gilbert / address@hidden / Manchester, UK
> 
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK