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Date: Fri, 26 Apr 2024 08:47:28 -0700
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Subject: Re: [PATCH 0/3] KVM: x86: Fix supported VM_TYPES caps
From: Sean Christopherson <seanjc@google.com>
To: Kai Huang <kai.huang@intel.com>
Cc: Xiaoyao Li <xiaoyao.li@intel.com>, "kvm@vger.kernel.org" <kvm@vger.kernel.org>, 
	"pbonzini@redhat.com" <pbonzini@redhat.com>, 
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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On Fri, Apr 26, 2024, Kai Huang wrote:
> On Thu, 2024-04-25 at 07:30 -0700, Sean Christopherson wrote:
> > On Thu, Apr 25, 2024, Xiaoyao Li wrote:
> > > On 4/24/2024 12:53 AM, Sean Christopherson wrote:
> > > > Fix a goof where KVM fails to re-initialize the set of supported VM=
 types,
> > > > resulting in KVM overreporting the set of supported types when a ve=
ndor
> > > > module is reloaded with incompatible settings.  E.g. unload kvm-int=
el.ko,
> > > > reload with ept=3D0, and KVM will incorrectly treat SW_PROTECTED_VM=
 as
> > > > supported.
> > >=20
> > > Hah, this reminds me of the bug of msrs_to_save[] and etc.
> > >=20
> > >    7a5ee6edb42e ("KVM: X86: Fix initialization of MSR lists")
> >=20
> > Yeah, and we had the same bug with allow_smaller_maxphyaddr
> >=20
> >   88213da23514 ("kvm: x86: disable the narrow guest module parameter on=
 unload")
> >=20
> > If the side effects of linking kvm.ko into kvm-{amd,intel}.ko weren't s=
o painful
> > for userspace,=C2=A0
> >=20
>=20
> Do we have any real side effects for _userspace_ here?

kvm.ko ceasing to exist, and "everything" being tied to the vendor module i=
s the
big problem.  E.g. params from the kernel command line for kvm.??? will bec=
ome
ineffective, etc.  Some of that can be handled in the kernel, e.g. KVM can =
create
a sysfs symlink so that the accesses through sysfs continue to work, but AF=
AIK
params don't supporting such aliasing/links.

I don't think there are any deal breakers, but I don't expect it to Just Wo=
rk either.