Re: [PATCH 10/25] KVM: TDX: Initialize KVM supported capabilities when module setup

Tony Lindgren
2024-10-10T09:49:22Z

On Thu, Oct 10, 2024 at 04:25:30PM +0800, Xiaoyao Li wrote:
> On 9/11/2024 7:04 PM, Tony Lindgren wrote:
> > On Tue, Sep 10, 2024 at 07:15:12PM +0200, Paolo Bonzini wrote:
> > > On 8/29/24 06:51, Tony Lindgren wrote:
> > > > > nit: Since there are other similarly named functions that come later how
> > > > > about rename this to init_kvm_tdx_caps, so that it's clear that the
> > > > > functions that are executed ones are prefixed with "init_" and those that
> > > > > will be executed on every TDV boot up can be named prefixed with "setup_"
> > > > We can call setup_kvm_tdx_caps() from from tdx_get_kvm_supported_cpuid(),
> > > > and drop the struct kvm_tdx_caps. So then the setup_kvm_tdx_caps() should
> > > > be OK.
> > >
> > > I don't understand this suggestion since tdx_get_capabilities() also needs
> > > kvm_tdx_caps. I think the code is okay as it is with just the rename that
> > > Nik suggested (there are already some setup_*() functions in KVM but for
> > > example setup_vmcs_config() is called from hardware_setup()).
> >
> > Oh sorry for the confusion, looks like I pasted the function names wrong
> > way around above and left out where setup_kvm_tdx_caps() can be called
> > from.
> >
> > I meant only tdx_get_capabilities() needs to call setup_kvm_tdx_caps().
> > And setup_kvm_tdx_caps() calls tdx_get_kvm_supported_cpuid().
> >
> > The data in kvm_tdx_caps is only needed for tdx_get_capabilities(). It can
> > be generated from the data already in td_conf.
> >
> > At least that's what it looks like to me, but maybe I'm missing something.
>
> kvm_tdx_caps is setup in __tdx_bringup() because it also serves the purpose
> to validate the KVM's capabilities against the specific TDX module. If KVM
> and TDX module are incompatible, it needs to fail the bring up of TDX in
> KVM. It's too late to validate it when KVM_TDX_CAPABILITIES issued. E.g.,
> if the TDX module reports some fixed-1 attribute bit while KVM isn't aware
> of, in such case KVM needs to set enable_tdx to 0 to reflect that TDX cannot
> be enabled/brought up.

OK makes sense, thanks for clarifying the use case for __tdx_bringup().

We can check the attributes_fixed1 and xfam_fixed1 also on __tdx_bringup()
no problem.

Regards,

Tony