linux-kernel - Re: [PATCH v3 07/12] x86/tdx: Make TDX_HYPERCALL asm similar to TDX_MODULE

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Date:   Thu, 3 Aug 2023 15:12:07 +0300
From:   "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>
To:     "Huang, Kai" <kai.huang@...el.com>
Cc:     "Hansen, Dave" <dave.hansen@...el.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "x86@...nel.org" <x86@...nel.org>, "bp@...en8.de" <bp@...en8.de>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "hpa@...or.com" <hpa@...or.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "n.borisov.lkml@...il.com" <n.borisov.lkml@...il.com>
Subject: Re: [PATCH v3 07/12] x86/tdx: Make TDX_HYPERCALL asm similar to
 TDX_MODULE_CALL

On Thu, Aug 03, 2023 at 11:56:40AM +0000, Huang, Kai wrote:
> On Thu, 2023-08-03 at 14:45 +0300, kirill.shutemov@...ux.intel.com wrote:
> > > > I would rather keep the struct
> > > > read-only where possible.
> > > > 
> > > 
> > > We can achieve this if there's a clean way to do, but I don't see that.
> > 
> > Keep _ret() and non-_ret() versions?
> 
> The problem is the assembly needs to always turn on the "\ret" so that the R10
> (used as VP.VMCALL leaf return code) can be saved to the structure.  Otherwise
> we are not able to return VP.VMCALL leaf return code.

Yeah. This is downside of single assembly macro for all calls.

One possible way is to make it in C: non-_ret() version pass to the
assembly helper copy of the caller's struct, keeping original intact.
But, yeah, it is ugly.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov