linux-kernel - Re: [PATCH v3 08/12] x86/tdx: Reimplement __tdx_hypercall() using TDX_MODULE

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Date:   Sun, 6 Aug 2023 14:25:50 +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 08/12] x86/tdx: Reimplement __tdx_hypercall() using
 TDX_MODULE_CALL asm

On Wed, Jul 26, 2023 at 11:25:10PM +1200, Kai Huang wrote:
> Now the TDX_HYPERCALL asm is basically identical to the TDX_MODULE_CALL
> with both '\saved' and '\ret' enabled, with two minor things though:
> 
> 1) The way to restore the structure pointer is different
> 
> The TDX_HYPERCALL uses RCX as spare to restore the structure pointer,
> but the TDX_MODULE_CALL assumes no spare register can be used.  In other
> words, TDX_MODULE_CALL already covers what TDX_HYPERCALL does.
> 
> 2) TDX_MODULE_CALL only clears shared registers for TDH.VP.ENTER
> 
> For this just need to make that code available for the non-host case.
> 
> Thus, remove the TDX_HYPERCALL and reimplement the __tdx_hypercall()
> using the TDX_MODULE_CALL.
> 
> Extend the TDX_MODULE_CALL to cover "clear shared registers" for
> TDG.VP.VMCALL.  Introduce a new __tdcall_saved_ret() to replace the
> temporary __tdcall_hypercall().
> 
> The __tdcall_saved_ret() can also be used for those new TDCALLs which
> require more input/output registers than the basic TDCALLs do.
> 
> Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Suggested-by: Peter Zijlstra <peterz@...radead.org>
> Signed-off-by: Kai Huang <kai.huang@...el.com>

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

-- 
  Kiryl Shutsemau / Kirill A. Shutemov