Re: [PATCH kvm-unit-tests] vmx: fixes for MAXPHYADDR requirement

["Radim Krčmář" <rkrcmar@redhat.com>]

2018-01-25 11:36-0500, Paolo Bonzini:
> ----- Original Message -----
> > From: "Radim Krčmář" <rkrcmar@redhat.com>
> > To: "Paolo Bonzini" <pbonzini@redhat.com>
> > Cc: kvm@vger.kernel.org
> > Sent: Thursday, January 25, 2018 4:11:32 PM
> > Subject: Re: [PATCH kvm-unit-tests] vmx: fixes for MAXPHYADDR requirement
> > 
> > 2018-01-17 19:03+0100, Paolo Bonzini:
> > > The EPT access tests require at least 41 bits of guest physical address
> > > space.  This is because the test data needs a separate PML4 entry in the
> > > EPT table.  However, many consumer-grade processors have only 36 or
> > > 39-bit MAXPHYADDR, and the tests fail there with a page fault due to
> > > reserved bits set in the guest (GVA->GPA) page tables.
> > > 
> > > Add a test on MAXPHYADDR and skip the tests if they cannot run on the
> > > system under test, and only require 40 bits to lower the requirements.
> > > 
> > > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> > > ---
> > >  x86/vmx_tests.c | 6 +++++-
> > >  1 file changed, 5 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/x86/vmx_tests.c b/x86/vmx_tests.c
> > > index e8c97f2..0c3b5a7 100644
> > > --- a/x86/vmx_tests.c
> > > +++ b/x86/vmx_tests.c
> > > @@ -2609,6 +2609,10 @@ static void ept_access_test_setup(void)
> > >  	if (setup_ept(false))
> > >  		test_skip("EPT not supported");
> > >  
> > > +	/* We use data->gpa = 1 << 39 so that test data has a separate pml4 entry
> > > */
> > > +	if (cpuid_maxphyaddr() < 40)
> > 
> > This does not help at the moment -- QEMU reports 40 even on hosts that
> > don't have as much.  It is a QEMU bug, so applied still, thanks.
> 
> True.  However, vmx.flat is run with "-cpu host,+vmx", and that should forward
> the host MAXPHYADDR, shouldn't it?

Would make sense for QEMU to do that, but it's not what happens.
I get 40 on both 39 and 46 hosts.

We can do "-cpu host,+vmx,host_phys_bits" at the cost of breaking unit
tests on old QEMUs ...