linux-kernel - Re: [PATCH v4 12/12] x86/virt/tdx: Adjust 'struct tdx_module

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Message-ID: <20230825234432.3ynoxtlguhqj4axl@box>
Date:   Sat, 26 Aug 2023 02:44:32 +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 v4 12/12] x86/virt/tdx: Adjust 'struct tdx_module_args'
 to use x86 "register index" layout

On Tue, Aug 15, 2023 at 11:02:06PM +1200, Kai Huang wrote:
> diff --git a/arch/x86/include/asm/shared/tdx.h b/arch/x86/include/asm/shared/tdx.h
> index 74fc466dfdcd..8d1427562c63 100644
> --- a/arch/x86/include/asm/shared/tdx.h
> +++ b/arch/x86/include/asm/shared/tdx.h
> @@ -58,24 +58,31 @@
>   * Used in __tdcall*() to gather the input/output registers' values of the
>   * TDCALL instruction when requesting services from the TDX module. This is a
>   * software only structure and not part of the TDX module/VMM ABI
> + *
> + * Note those *_unused are not used by the TDX_MODULE_CALL assembly.
> + * The layout of this structure also matches KVM's kvm_vcpu_arch::regs[]
> + * layout, which follows the "register index" order of x86 GPRs.  KVM
> + * then can simply type cast kvm_vcpu_arch::regs[] to this structure to
> + * avoid the extra memory copy between two structures when making
> + * TDH.VP.ENTER SEAMCALL.

I still don't like KVM details leak here. I don't feel strong enough about
it to NAK the patch, but...

-- 
  Kiryl Shutsemau / Kirill A. Shutemov