Re: [PATCH v2] KVM: x86: Assume a 64-bit hypercall for guests with protected state

[Tom Lendacky]

On 10/26/21 1:03 PM, Tom Lendacky wrote:
> On 10/1/21 12:06 PM, Tom Lendacky wrote:
> > On 5/25/21 1:25 AM, Vitaly Kuznetsov wrote:
> > > Tom Lendacky <thomas.lendacky@xxxxxxx> writes:
> > >
> > > > When processing a hypercall for a guest with protected state, currently
> > > > SEV-ES guests, the guest CS segment register can't be checked to
> > > > determine if the guest is in 64-bit mode. For an SEV-ES guest, it is
> > > > expected that communication between the guest and the hypervisor is
> > > > performed to shared memory using the GHCB. In order to use the GHCB, the
> > > > guest must have been in long mode, otherwise writes by the guest to the
> > > > GHCB would be encrypted and not be able to be comprehended by the
> > > > hypervisor.
> > > >
> > > > Create a new helper function, is_64_bit_hypercall(), that assumes the
> > > > guest is in 64-bit mode when the guest has protected state, and returns
> > > > true, otherwise invoking is_64_bit_mode() to determine the mode. Update
> > > > the hypercall related routines to use is_64_bit_hypercall() instead of
> > > > is_64_bit_mode().
> > > >
> > > > Add a WARN_ON_ONCE() to is_64_bit_mode() to catch occurences of calls to
> > > > this helper function for a guest running with protected state.
> > > >
> > > > Fixes: f1c6366e3043 ("KVM: SVM: Add required changes to support 
> > > > intercepts under SEV-ES")
> > > > Reported-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> > > > Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
> > > > ---

...

> > > Reviewed-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
> > >
> > > Thanks!
> >
> > Paolo,
> >
> > This got lost in my stack of work... any comments?
> >
> > Thanks,
> > Tom
>
> Ping
>
> Thanks,
> Tom

Another ping on this.

Paolo, you had replied "queued" on the v1, but came up with a suggestion
for a v2 that might have got lost in the replies because it never got
queued. Here are the threads:

v1: https://lore.kernel.org/kvm/d0904f0d049300267665bd4abf96c3d7e7aa4825.1621701837.git.thomas.lendacky@xxxxxxx/

v2: https://lore.kernel.org/kvm/e0b20c770c9d0d1403f23d83e785385104211f74.1621878537.git.thomas.lendacky@xxxxxxx/

Thanks,
Tom

> > >