linux-kernel - Re: [PATCH v3 10/12] x86/virt/tdx: Wire up basic SEAMCALL functions

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Date:   Sun, 6 Aug 2023 14:36:23 +0300
From:   kirill.shutemov@...ux.intel.com
To:     Kai Huang <kai.huang@...el.com>
Cc:     peterz@...radead.org, linux-kernel@...r.kernel.org,
        dave.hansen@...el.com, tglx@...utronix.de, bp@...en8.de,
        mingo@...hat.com, hpa@...or.com, x86@...nel.org, seanjc@...gle.com,
        pbonzini@...hat.com, isaku.yamahata@...el.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com,
        n.borisov.lkml@...il.com
Subject: Re: [PATCH v3 10/12] x86/virt/tdx: Wire up basic SEAMCALL functions

On Wed, Jul 26, 2023 at 11:25:12PM +1200, Kai Huang wrote:
> Intel Trust Domain Extensions (TDX) protects guest VMs from malicious
> host and certain physical attacks.  A CPU-attested software module
> called 'the TDX module' runs inside a new isolated memory range as a
> trusted hypervisor to manage and run protected VMs.
> 
> TDX introduces a new CPU mode: Secure Arbitration Mode (SEAM).  This
> mode runs only the TDX module itself or other code to load the TDX
> module.
> 
> The host kernel communicates with SEAM software via a new SEAMCALL
> instruction.  This is conceptually similar to a guest->host hypercall,
> except it is made from the host to SEAM software instead.  The TDX
> module establishes a new SEAMCALL ABI which allows the host to
> initialize the module and to manage VMs.
> 
> The SEAMCALL ABI is very similar to the TDCALL ABI and leverages much
> TDCALL infrastructure.  Wire up basic functions to make SEAMCALLs for
> the basic support of running TDX guests: __seamcall(), __seamcall_ret(),
> and __seamcall_saved_ret() for TDH.VP.ENTER.  All SEAMCALLs involved in
> the basic TDX support don't use "callee-saved" registers as input and
> output, except the TDH.VP.ENTER.
> 
> To start to support TDX, create a new arch/x86/virt/vmx/tdx/tdx.c for
> TDX host kernel support.  Add a new Kconfig option CONFIG_INTEL_TDX_HOST
> to opt-in TDX host kernel support (to distinguish with TDX guest kernel
> support).  So far only KVM uses TDX.  Make the new config option depend
> on KVM_INTEL.
> 
> Signed-off-by: Kai Huang <kai.huang@...el.com>
> ---
> 
> v2 -> v3:
>  - Added __seamcall_saved_ret() back for TDH.VP.ENTER, given the new
>    patch to adjust 'struct tdx_module_args' layout.
> 
> v1 -> v2:
>  - Removed __seamcall_saved_ret() and leave it to KVM TDX patches.
> 
> ---
>  arch/x86/Kconfig                 | 12 +++++++
>  arch/x86/Makefile                |  2 ++
>  arch/x86/include/asm/tdx.h       |  7 ++++
>  arch/x86/virt/Makefile           |  2 ++
>  arch/x86/virt/vmx/Makefile       |  2 ++
>  arch/x86/virt/vmx/tdx/Makefile   |  2 ++
>  arch/x86/virt/vmx/tdx/seamcall.S | 61 ++++++++++++++++++++++++++++++++
>  7 files changed, 88 insertions(+)
>  create mode 100644 arch/x86/virt/Makefile
>  create mode 100644 arch/x86/virt/vmx/Makefile
>  create mode 100644 arch/x86/virt/vmx/tdx/Makefile
>  create mode 100644 arch/x86/virt/vmx/tdx/seamcall.S
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 7422db409770..0558dd98abd7 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -1949,6 +1949,18 @@ config X86_SGX
>  
>  	  If unsure, say N.
>  
> +config INTEL_TDX_HOST
> +	bool "Intel Trust Domain Extensions (TDX) host support"
> +	depends on CPU_SUP_INTEL
> +	depends on X86_64
> +	depends on KVM_INTEL

Hm. I expected KVM_INTEL to depend on CPU_SUP_INTEL, but apparently no.
Any reasons why?

Anyway, it is not strictly related to the patch:

Reviewed-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

-- 
  Kiryl Shutsemau / Kirill A. Shutemov