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

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Liran Alon (liran.alon@oracle.com) wrote:
> 
> > On 18 Jun 2019, at 12:03, Dr. David Alan Gilbert <dgilbert@redhat.com> wrote:
> > 
> > * Liran Alon (liran.alon@oracle.com) 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 / dgilbert@redhat.com / Manchester, UK
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK