Re: [PATCH v1 03/11] x86/cpufeatures: Add TDX Guest CPU feature

[Kuppuswamy, Sathyanarayanan]

Hi,

On 6/10/21 5:28 AM, Borislav Petkov wrote:
> On Tue, Jun 01, 2021 at 07:21:28PM -0700, Kuppuswamy Sathyanarayanan wrote:
> > Add CPU feature detection for Trusted Domain Extensions support.
> > TDX feature adds capabilities to keep guest register state and
> > memory isolated from hypervisor.
> >
> > For TDX guest platforms, executing CPUID(0x21, 0) will return
>
> I'm assuming that 0 is ECX?

Correct. I will clarify it in commit log.

> > following values in EAX, EBX, ECX and EDX.
> >
> > EAX:  Maximum sub-leaf number:  0
> > EBX/EDX/ECX:  Vendor string:
> >
> > EBX =  "Inte"
> > EDX =  "lTDX"
> > ECX =  "    "
> >
> > So when above condition is true, set X86_FEATURE_TDX_GUEST
> > feature cap bit
> 		 ^
> 		 Fullstop.

Will fix it in next version.

> > diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> > index ac37830ae941..dddc3a27cc8a 100644
> > --- a/arch/x86/include/asm/cpufeatures.h
> > +++ b/arch/x86/include/asm/cpufeatures.h
> > @@ -238,6 +238,7 @@
> >   #define X86_FEATURE_VMW_VMMCALL		( 8*32+19) /* "" VMware prefers VMMCALL hypercall instruction */
> >   #define X86_FEATURE_PVUNLOCK		( 8*32+20) /* "" PV unlock function */
> >   #define X86_FEATURE_VCPUPREEMPT		( 8*32+21) /* "" PV vcpu_is_preempted function */
> > +#define X86_FEATURE_TDX_GUEST		( 8*32+22) /* Trusted Domain Extensions Guest */
>
> What's the name of the feature bit? "TDX guest"? Why not only
> X86_FEATURE_TDX and then you can have "tdx" in cpuinfo?

Make sense. I can change it to "TDX". I guess we will not a feature bit
for "tdx host"

> >   
> >   /* Intel-defined CPU features, CPUID level 0x00000007:0 (EBX), word 9 */
> >   #define X86_FEATURE_FSGSBASE		( 9*32+ 0) /* RDFSBASE, WRFSBASE, RDGSBASE, WRGSBASE instructions*/
> > diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
> > new file mode 100644
> > index 000000000000..679500e807f3
> > --- /dev/null
> > +++ b/arch/x86/include/asm/tdx.h
> > @@ -0,0 +1,20 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/* Copyright (C) 2020 Intel Corporation */
> > +#ifndef _ASM_X86_TDX_H
> > +#define _ASM_X86_TDX_H
> > +
> > +#define TDX_CPUID_LEAF_ID	0x21
> > +
> > +#ifdef CONFIG_INTEL_TDX_GUEST
> > +
> > +#include <asm/cpufeature.h>
>
> As before - put the include at the top.

I will change it.

> > +void __init tdx_early_init(void);
> > +
> > +#else // !CONFIG_INTEL_TDX_GUEST
>
> No need for that // - comment

I will remove it in next version.

> > diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
> > new file mode 100644
> > index 000000000000..5b14b72e41c5
> > --- /dev/null
> > +++ b/arch/x86/kernel/tdx.c
> > @@ -0,0 +1,30 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/* Copyright (C) 2020 Intel Corporation */
> > +
> > +#include <asm/tdx.h>
> > +
> > +static inline bool cpuid_has_tdx_guest(void)
> > +{
> > +	u32 eax, signature[3];
>
> Shorten that array name to "sig" so that you don't have to break the
> cpuid_count() line below.

I will fix it in next version.

> > +
> > +	if (cpuid_eax(0) < TDX_CPUID_LEAF_ID)
> > +		return false;
> > +
> > +	cpuid_count(TDX_CPUID_LEAF_ID, 0, &eax, &signature[0],
> > +		    &signature[1], &signature[2]);
> > +
> > +	if (memcmp("IntelTDX    ", signature, 12))
> > +		return false;
> > +
> > +	return true;
>
> or simply:
>
> return !memcmp(...

Got it. I will change it in next version.

> > +}
> > +
> > +void __init tdx_early_init(void)
> > +{
> > +	if (!cpuid_has_tdx_guest())
> > +		return;
> > +
> > +	setup_force_cpu_cap(X86_FEATURE_TDX_GUEST);
> > +
> > +	pr_info("TDX guest is initialized\n");
>
> Use pr_fmt in this file:
>
> #undef pr_fmt
> #define pr_fmt(fmt)     "x86/tdx: " fmt
>
> and then do
>
> 	pr_info("Guest initialized\n");

Patch titled "x86/tdx: Add __tdx_module_call() and __tdx_hypercall() helper functions" add
it. It makes sense to move it to this patch.

> Thx.

--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer