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

[Nikolay Borisov]

On 5.09.24 г. 16:36 ч., Xiaoyao Li wrote:
> On 9/4/2024 7:58 PM, Nikolay Borisov wrote:
> > On 13.08.24 г. 1:48 ч., Rick Edgecombe wrote:
> > > From: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
> > >
> > > While TDX module reports a set of capabilities/features that it
> > > supports, what KVM currently supports might be a subset of them.
> > > E.g., DEBUG and PERFMON are supported by TDX module but currently not
> > > supported by KVM.
> > >
> > > Introduce a new struct kvm_tdx_caps to store KVM's capabilities of TDX.
> > > supported_attrs and suppported_xfam are validated against fixed0/1
> > > values enumerated by TDX module. Configurable CPUID bits derive from TDX
> > > module plus applying KVM's capabilities (KVM_GET_SUPPORTED_CPUID),
> > > i.e., mask off the bits that are configurable in the view of TDX module
> > > but not supported by KVM yet.
> > >
> > > KVM_TDX_CPUID_NO_SUBLEAF is the concept from TDX module, switch it to 0
> > > and use KVM_CPUID_FLAG_SIGNIFCANT_INDEX, which are the concept of KVM.
> > >
> > > Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
> > > Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
> > > ---
> > > uAPI breakout v1:
> > >   - Change setup_kvm_tdx_caps() to use the exported 'struct tdx_sysinfo'
> > >     pointer.
> > >   - Change how to copy 'kvm_tdx_cpuid_config' since 'struct tdx_sysinfo'
> > >     doesn't have 'kvm_tdx_cpuid_config'.
> > >   - Updates for uAPI changes
> > > ---
> > >   arch/x86/include/uapi/asm/kvm.h |  2 -
> > >   arch/x86/kvm/vmx/tdx.c          | 81 +++++++++++++++++++++++++++++++++
> > >   2 files changed, 81 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/arch/x86/include/uapi/asm/kvm.h 
> > > b/arch/x86/include/uapi/asm/kvm.h
> > > index 47caf508cca7..c9eb2e2f5559 100644
> > > --- a/arch/x86/include/uapi/asm/kvm.h
> > > +++ b/arch/x86/include/uapi/asm/kvm.h
> > > @@ -952,8 +952,6 @@ struct kvm_tdx_cmd {
> > >       __u64 hw_error;
> > >   };
> > > -#define KVM_TDX_CPUID_NO_SUBLEAF    ((__u32)-1)
> > > -
> > >   struct kvm_tdx_cpuid_config {
> > >       __u32 leaf;
> > >       __u32 sub_leaf;
> > > diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> > > index 90b44ebaf864..d89973e554f6 100644
> > > --- a/arch/x86/kvm/vmx/tdx.c
> > > +++ b/arch/x86/kvm/vmx/tdx.c
> > > @@ -31,6 +31,19 @@ static void __used tdx_guest_keyid_free(int keyid)
> > >       ida_free(&tdx_guest_keyid_pool, keyid);
> > >   }
> > > +#define KVM_TDX_CPUID_NO_SUBLEAF    ((__u32)-1)
> > > +
> > > +struct kvm_tdx_caps {
> > > +    u64 supported_attrs;
> > > +    u64 supported_xfam;
> > > +
> > > +    u16 num_cpuid_config;
> > > +    /* This must the last member. */
> > > +    DECLARE_FLEX_ARRAY(struct kvm_tdx_cpuid_config, cpuid_configs);
> > > +};
> > > +
> > > +static struct kvm_tdx_caps *kvm_tdx_caps;
> > > +
> > >   static int tdx_get_capabilities(struct kvm_tdx_cmd *cmd)
> > >   {
> > >       const struct tdx_sysinfo_td_conf *td_conf = &tdx_sysinfo->td_conf;
> > > @@ -131,6 +144,68 @@ int tdx_vm_ioctl(struct kvm *kvm, void __user 
> > > *argp)
> > >       return r;
> > >   }
> > > +#define KVM_SUPPORTED_TD_ATTRS (TDX_TD_ATTR_SEPT_VE_DISABLE)
> >
> > Why isn't TDX_TD_ATTR_DEBUG added as well?
>
> Because so far KVM doesn't support all the features of a DEBUG TD for 
> userspace. e.g., KVM doesn't provide interface for userspace to 
> read/write private memory of DEBUG TD.

But this means that you can't really run a TDX with SEPT_VE_DISABLE 
disabled for debugging purposes, so perhaps it might be necessary to 
rethink the condition allowing SEPT_VE_DISABLE to be disabled. Without 
the debug flag and SEPT_VE_DISABLE disabled the code refuses to start 
the VM, what if one wants to debug some SEPT issue by having an oops 
generated inside the vm ?

> > <snip>