Re: [PATCH v2] KVM: nVMX: Advertise IA32_PAT in VM exit control

[Gleb Natapov <gleb@redhat.com>]

On Mon, Aug 05, 2013 at 08:03:31AM -0400, Paolo Bonzini wrote:
> 
> 
> ----- Original Message -----
> > From: "Arthur Chunqi Li" <yzt356@gmail.com>
> > To: kvm@vger.kernel.org
> > Cc: "jan kiszka" <jan.kiszka@web.de>, gleb@redhat.com, pbonzini@redhat.com, "Arthur Chunqi Li" <yzt356@gmail.com>
> > Sent: Monday, August 5, 2013 1:18:13 PM
> > Subject: [PATCH v2] KVM: nVMX: Advertise IA32_PAT in VM exit control
> > 
> > Advertise VM_EXIT_SAVE_IA32_PAT and VM_EXIT_LOAD_IA32_PAT.
> > 
> > Signed-off-by: Arthur Chunqi Li <yzt356@gmail.com>
> > ---
> > 
> > ChangeLog to v1:
> > 	Add host features check. Format is the same as "entry controls".
> > 
> >  arch/x86/kvm/vmx.c |   10 ++++++----
> >  1 file changed, 6 insertions(+), 4 deletions(-)
> > 
> > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> > index 396572d..fd451c1 100644
> > --- a/arch/x86/kvm/vmx.c
> > +++ b/arch/x86/kvm/vmx.c
> > @@ -2191,14 +2191,16 @@ static __init void nested_vmx_setup_ctls_msrs(void)
> >  	 * If bit 55 of VMX_BASIC is off, bits 0-8 and 10, 11, 13, 14, 16 and
> >  	 * 17 must be 1.
> >  	 */
> > +	rdmsr(MSR_IA32_VMX_EXIT_CTLS,
> > +		nested_vmx_exit_ctls_low, nested_vmx_exit_ctls_high);
> >  	nested_vmx_exit_ctls_low = VM_EXIT_ALWAYSON_WITHOUT_TRUE_MSR;
> > +	nested_vmx_exit_ctls_high &=
> > +		VM_EXIT_LOAD_IA32_PAT | VM_EXIT_SAVE_IA32_PAT;
> > +	nested_vmx_exit_ctls_high |= VM_EXIT_ALWAYSON_WITHOUT_TRUE_MSR;
> >  	/* Note that guest use of VM_EXIT_ACK_INTR_ON_EXIT is not supported. */
> >  #ifdef CONFIG_X86_64
> > -	nested_vmx_exit_ctls_high = VM_EXIT_HOST_ADDR_SPACE_SIZE;
> > -#else
> > -	nested_vmx_exit_ctls_high = 0;
> > +	nested_vmx_exit_ctls_high |= VM_EXIT_HOST_ADDR_SPACE_SIZE;
> 
> I think you should clear the bit if !X86_64 (and not do anything if
> X86_64, the bit should be already set in MSR_IA32_VMX_EXIT_CTLS).
> 
Yes, we do not support 64 bit guests on 32bit host. It means that 32 bit
host is essentially "processors that do not support Intel 64 architecture",
so the control should be zero.

--
			Gleb.