Re: [PATCH v5 09/12] x86/tdx: Wire up KVM hypercalls

[Kuppuswamy, Sathyanarayanan]

On 8/24/21 9:34 AM, Borislav Petkov wrote:
> On Wed, Aug 04, 2021 at 11:13:26AM -0700, Kuppuswamy Sathyanarayanan wrote:
> > From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> >
> > KVM hypercalls use the "vmcall" or "vmmcall" instructions.
>
> Write instruction mnemonics in all caps pls.

Ok. I will change it in next submission.

> > +# This option enables KVM specific hypercalls in TDX guest.
> > +config INTEL_TDX_GUEST_KVM
>
> What is that config option really for? IOW, can't you use
> CONFIG_KVM_GUEST instead?
Since TDX code can be used by other hypervisor (non KVM case) we
want to have a config to differentiate the KVM related calls.

> > +	def_bool y
> > +	depends on KVM_GUEST && INTEL_TDX_GUEST
> > +
> >   endif #HYPERVISOR_GUEST
> >   
> >   source "arch/x86/Kconfig.cpu"
> > diff --git a/arch/x86/include/asm/asm-prototypes.h b/arch/x86/include/asm/asm-prototypes.h
> > index 4cb726c71ed8..9855a9ff2924 100644
> > --- a/arch/x86/include/asm/asm-prototypes.h
> > +++ b/arch/x86/include/asm/asm-prototypes.h
> > @@ -17,6 +17,10 @@
> >   extern void cmpxchg8b_emu(void);
> >   #endif
> >   
> > +#ifdef CONFIG_INTEL_TDX_GUEST
> > +#include <asm/tdx.h>
> > +#endif
>
> What "ASM sysmbol generation issue" forced this?

Compiler raised version generation issue for __tdx_hypercall

> ...
>
> > diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
> > index 846fe58f0426..8fa33e2c98db 100644
> > --- a/arch/x86/include/asm/tdx.h
> > +++ b/arch/x86/include/asm/tdx.h
> > @@ -6,8 +6,9 @@
> >   #include <linux/cpufeature.h>
> >   #include <linux/types.h>
> >   
> > -#define TDX_CPUID_LEAF_ID	0x21
> > -#define TDX_HYPERCALL_STANDARD  0
> > +#define TDX_CPUID_LEAF_ID			0x21
> > +#define TDX_HYPERCALL_STANDARD			0
> > +#define TDX_HYPERCALL_VENDOR_KVM		0x4d564b2e584454
>
> 						"TDX.KVM"
>
> Yeah, you can put it in a comment so that people don't have to do the
> CTRL-V game in vim insert mode, i.e., ":help i_CTRL-V_digit" :-)

Got it. I will add it in comment.

> >   /*
> >    * Used in __tdx_module_call() helper function to gather the
> > @@ -80,4 +81,29 @@ static inline bool tdx_prot_guest_has(unsigned long flag) { return false; }
> >   
> >   #endif /* CONFIG_INTEL_TDX_GUEST */
> >   
> > +#ifdef CONFIG_INTEL_TDX_GUEST_KVM
>
> I don't think that even needs the ifdeffery. If it is not used, the
> inline will simply get discarded so why bother?

It makes sense. I can remove it.

> > +
> > +static inline long tdx_kvm_hypercall(unsigned int nr, unsigned long p1,
> > +				     unsigned long p2, unsigned long p3,
> > +				     unsigned long p4)
> > +{
> > +	struct tdx_hypercall_output out;
> > +	u64 err;
> > +
> > +	err = __tdx_hypercall(TDX_HYPERCALL_VENDOR_KVM, nr, p1, p2,
> > +			      p3, p4, &out);
> > +
> > +	BUG_ON(err);
> > +
> > +	return out.r10;
> > +}
> > +#else
> > +static inline long tdx_kvm_hypercall(unsigned int nr, unsigned long p1,
> > +				     unsigned long p2, unsigned long p3,
> > +				     unsigned long p4)
> > +{
> > +	return -ENODEV;
> > +}
> > +#endif /* CONFIG_INTEL_TDX_GUEST_KVM */
> > +
> >   #endif /* _ASM_X86_TDX_H */
> > diff --git a/arch/x86/kernel/tdcall.S b/arch/x86/kernel/tdcall.S
> > index 9df94f87465d..1823bac4542d 100644
> > --- a/arch/x86/kernel/tdcall.S
> > +++ b/arch/x86/kernel/tdcall.S
> > @@ -3,6 +3,7 @@
> >   #include <asm/asm.h>
> >   #include <asm/frame.h>
> >   #include <asm/unwind_hints.h>
> > +#include <asm/export.h>
> >   
> >   #include <linux/linkage.h>
> >   #include <linux/bits.h>
> > @@ -309,3 +310,4 @@ skip_sti:
> >   
> >          retq
> >   SYM_FUNC_END(__tdx_hypercall)
> > +EXPORT_SYMBOL(__tdx_hypercall);
>
> EXPORT_SYMBOL_GPL, of course.

Yes. I will fix this in next version.

>

--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer