Re: [RFC][PATCH] ignore set_cr3 GP fault in non-pae mode

[Ryan Harper <ryanh-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>]

* Zachary Amsden <zach-pghWNbHTmq7QT0dZR+AlfA@public.gmane.org> [2007-09-18 16:59]:
> On Tue, 2007-09-18 at 16:25 -0500, Ryan Harper wrote:
> > * Nakajima, Jun <jun.nakajima-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org> [2007-09-18 16:22]:
> > > Anthony Liguori wrote:
> > > > Ryan Harper wrote:
> > > > > Playing around with running VMware-server within a KVM guest and
> > > noticed
> > > > > that whenever we launch a VM within the guest, KVM reports a GP
> > > fault in
> > > > > set_cr3.  Removing the fault injection (raised for attempting to set
> > > > > reserved bits) for the non-pae case allows memtest to boot and run
> > > > > within VMWare Server, running in a KVM Linux guest.
> > > > > 
> > > > > This same test (Linux, VMware-server, booting/running memtest iso)
> > > works
> > > > > fine on bare-metal.  Thoughts?
> > > > > 
> > > > 
> > > > Setting reserved bits is different from setting MBZ bits since the
> > > > behaviors undefined.  If something as common as VMware is depending on
> > > > being able to set a reserved bit then perhaps the right thing to do
> > > from
> > > > KVM's perspective is to let it.
> > > > 
> > > > I'm curious if Zach or Jun have any comments about the right thing to
> > > do
> > > > here.
> > > > 
> > > 
> > > As long as the guest is protected mode (unlike the long mode), the Intel
> > > spec does _not_ say that reserved bits checking is enforced for CR3. As
> > > far as I looked at the AMD spec, looks like #GP is caused even in
> > > protected mode... Does the test work for AMD systems?
> > 
> > I ran my test on an AMD host.
> 
> We have a test which verifies #GP is not caused by setting the bits on
> either AMD or Intel chips.  "Stray" bits can get turned on in some cases
> when switching between 64-bit, PAE and non-PAE address modes.
> 
> Were you testing on a 64-bit host kernel?

64-bit Host running 32-bit KVM Guest. VMware-server shouldn't be seeing
anything 64-bit AFAIK.


> 
> Zach

-- 
Ryan Harper
Software Engineer; Linux Technology Center
IBM Corp., Austin, Tx
(512) 838-9253   T/L: 678-9253
ryanh-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org

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