Re: [RFC][PATCH] Add support for the GUEST_SMBASE VMCS field for Intel VT-x.

[Matthias Lange <mlange@sec.t-labs.tu-berlin.de>]

On Sun, May 20, 2012 at 03:39:30PM +0300, Avi Kivity wrote:
> On 05/18/2012 12:34 PM, Matthias Lange wrote:
> > The following patch adds support for the GUEST_SMBASE field. This allows
> > hypervisors running inside kvm read/write access to this field. I have
> > tested this to work on a Core i5 machine.
> >
> > diff --git a/arch/x86/include/asm/vmx.h b/arch/x86/include/asm/vmx.h
> > index 31f180c..6a14720 100644
> > --- a/arch/x86/include/asm/vmx.h
> > +++ b/arch/x86/include/asm/vmx.h
> > @@ -194,6 +194,7 @@ enum vmcs_field {
> >  	GUEST_TR_AR_BYTES               = 0x00004822,
> >  	GUEST_INTERRUPTIBILITY_INFO     = 0x00004824,
> >  	GUEST_ACTIVITY_STATE            = 0X00004826,
> > +	GUEST_SMBASE			= 0x00004828,
> >  	GUEST_SYSENTER_CS               = 0x0000482A,
> >  	HOST_IA32_SYSENTER_CS           = 0x00004c00,
> >  	CR0_GUEST_HOST_MASK             = 0x00006000,
> > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> > index 4ff0ab9..0063743 100644
> > --- a/arch/x86/kvm/vmx.c
> > +++ b/arch/x86/kvm/vmx.c
> > @@ -285,6 +285,7 @@ struct __packed vmcs12 {
> >  	u32 guest_tr_ar_bytes;
> >  	u32 guest_interruptibility_info;
> >  	u32 guest_activity_state;
> > +	u32 guest_smbase;
> >  	u32 guest_sysenter_cs;
> >  	u32 host_ia32_sysenter_cs;
> >  	u32 padding32[8]; /* room for future expansion */
> > @@ -546,6 +547,7 @@ static unsigned short vmcs_field_to_offset_table[] = {
> >
> 
> vmcs12 is an ABI, so you can't insert fields at random.  Grab one from
> padding32.

Do you mean the ABI defined in the Intel Software Developer's manual 3B? Or is
vmcs12 only an ABI internal to the kvm module?

I understand that my patch is wrong because I need to decrease the size of
padding32. I tested the patch by running Ubuntu 12.04 as the L1 guest and
Tinycore Linux as the L2 guest.

Let me know what you think.

Matthias.


-- 
Dipl.-Inf. Matthias Lange <mlange@sec.t-labs.tu-berlin.de>
Security in Telecommunications
TU Berlin / Telekom Innovation Laboratories
Ernst-Reuter-Platz 7, 10587 Berlin
Phone: +49 - 30 - 8353 58 553
Mobile: +49 - 160 - 587 28 07
Web: http://www.t-labs.tu-berlin.de/sect