Re: [Xen-devel] [PATCH 18/18] PVH xen: introduce vmx_pvh.c

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 03.07.13 at 03:40, Mukesh Rathor <mukesh.rathor@xxxxxxxxxx> wrote:
> On Fri, 28 Jun 2013 10:44:08 +0100
> "Jan Beulich" <JBeulich@xxxxxxxx> wrote:
> 
>> >>> On 28.06.13 at 04:28, Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>
>> >>> wrote:
>> > On Tue, 25 Jun 2013 11:49:57 +0100 "Jan Beulich"
>> > <JBeulich@xxxxxxxx> wrote:
> ...... 
>> And btw., looking at that patch again I'm also getting the
>> impression that the GS base handling in that function is lacking
>> consideration of VGCF_in_kernel.
> 
> I still fail to see what VGCF_in_kernel has to do with GS base for 
> PVH guest. The flag should be irrelevant for PVH IMO. Can you kindly
> elaborate a bit?

VGCF_in_kernel specifies whether a guest wants to start its vCPU
in user of kernel mode (why the interface permits that is another
question, but you have to play by what is there).

The CPU notion of the two GS bases is "active" and "shadow",
with no meaning associated whether one is the kernel's and the
other is for user mode.

The Xen notion otoh is "gs_base_kernel" and "gs_base_user".
Which VMCS field needs to be populated with which of the two
struct vcpu_guest_context values thus depends on said flag.

Jan


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