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

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Message-ID: <YSUfpQPvL6wsk6Ou@zn.tnic>
Date:   Tue, 24 Aug 2021 18:34:45 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Peter H Anvin <hpa@...or.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 09/12] x86/tdx: Wire up KVM hypercalls

On Wed, Aug 04, 2021 at 11:13:26AM -0700, Kuppuswamy Sathyanarayanan wrote:
> From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> 
> KVM hypercalls use the "vmcall" or "vmmcall" instructions.

Write instruction mnemonics in all caps pls.

> +# 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?

> +	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?

...

> 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" :-)

>  /*
>   * 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?

> +
> +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.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette