linux-kernel - Re: [PATCH v4 00/12] Unify TDCALL/SEAMCALL and TDVMCALL assembly

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Date:   Thu, 14 Sep 2023 00:45:49 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "isaku.yamahata@...ux.intel.com" <isaku.yamahata@...ux.intel.com>
CC:     "Hansen, Dave" <dave.hansen@...el.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "bp@...en8.de" <bp@...en8.de>, "x86@...nel.org" <x86@...nel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "hpa@...or.com" <hpa@...or.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "n.borisov.lkml@...il.com" <n.borisov.lkml@...il.com>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Subject: Re: [PATCH v4 00/12] Unify TDCALL/SEAMCALL and TDVMCALL assembly

On Wed, 2023-09-13 at 17:22 -0700, Isaku Yamahata wrote:
> On Tue, Sep 05, 2023 at 11:01:28PM +0000,
> "Huang, Kai" <kai.huang@...el.com> wrote:
> 
> > On Tue, 2023-08-15 at 23:01 +1200, Kai Huang wrote:
> > > Hi Peter, Kirill,
> > > 
> > > This series unifies the assembly code for TDCALL/SEAMCALL and TDVMCALL.
> > > Now all of them use one singe TDX_MODULE_CALL asm macro.  More
> > > information please see cover letter of v2 (see link below).
> > > 
> > > Tested by booting TDX guest, initializing TDX module, and running TDX
> > > guest successfully, all with this series applied.
> > > 
> > > 
> > 
> > Hi Peter,
> > 
> > Sorry to ping, but could you take a look whether you are OK with this series?
> > 
> > Basically Kirill has provided his Reviewed-by for all the patches except the
> > last one (Add unused registers to 'struct tdx_module_args' to optimize VP.ENTER
> > for KVM), which he didn't like.  But it is pretty much a standalone optimization
> > patch we either can have or drop when applying, so I'll leave to you.
> > 
> > Also feel free to let me know if I can help you on anything to offload part of
> > your load? :-)
> 
> Because the optimization patch was dropped in tip x86/tdx tree, TDX KVM can't
> use __seamcall_saved_ret() because the argument doesn't match.  There is no
> user of __seamcall_saved_ret().
> 

I agree sometimes "optimization" is better to have, but functionally we
certainly don't depend on "optimization" to work, so sure KVM TDX can use it (of
course I will leave to maintainers though).