linux-kernel - Re: [PATCH v2 4/6] x86/tdx: Expand __tdx_hypercall() to handle more arguments

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Date:   Fri, 9 Dec 2022 01:06:38 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Dexuan Cui <decui@...rosoft.com>
Cc:     Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "arnd@...db.de" <arnd@...db.de>, "bp@...en8.de" <bp@...en8.de>,
        "brijesh.singh@....com" <brijesh.singh@....com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "jane.chu@...cle.com" <jane.chu@...cle.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        KY Srinivasan <kys@...rosoft.com>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "luto@...nel.org" <luto@...nel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "seanjc@...gle.com" <seanjc@...gle.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "tony.luck@...el.com" <tony.luck@...el.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "Michael Kelley (LINUX)" <mikelley@...rosoft.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 4/6] x86/tdx: Expand __tdx_hypercall() to handle more
 arguments

On Thu, Dec 08, 2022 at 03:54:32PM +0000, Dexuan Cui wrote:
> > From: Sathyanarayanan Kuppuswamy
> > Sent: Wednesday, December 7, 2022 2:14 PM
> >  [...]
> > > --- a/arch/x86/coco/tdx/tdcall.S
> > > +++ b/arch/x86/coco/tdx/tdcall.S
> > > @@ -13,6 +13,12 @@
> > >  /*
> > >   * Bitmasks of exposed registers (with VMM).
> > >   */
> > > +#define TDX_RDX		BIT(2)
> > > +#define TDX_RBX		BIT(3)
> > > +#define TDX_RSI		BIT(6)
> > > +#define TDX_RDI		BIT(7)
> > > +#define TDX_R8		BIT(8)
> > > +#define TDX_R9		BIT(9)
> > >  #define TDX_R10		BIT(10)
> > >  #define TDX_R11		BIT(11)
> > >  #define TDX_R12		BIT(12)
> > > @@ -27,9 +33,9 @@
> > >   * details can be found in TDX GHCI specification, section
> > >   * titled "TDCALL [TDG.VP.VMCALL] leaf".
> > >   */
> > > -#define TDVMCALL_EXPOSE_REGS_MASK	( TDX_R10 | TDX_R11 | \
> > > -					  TDX_R12 | TDX_R13 | \
> > > -					  TDX_R14 | TDX_R15 )
> > > +#define TDVMCALL_EXPOSE_REGS_MASK	\
> > > +	( TDX_RDX | TDX_RBX | TDX_RSI | TDX_RDI | TDX_R8  | TDX_R9  | \
> > > +	  TDX_R10 | TDX_R11 | TDX_R12 | TDX_R13 | TDX_R14 | TDX_R15 )
> > >
> > 
> > You seem to have expanded the list to include all VMCALL supported
> > registers except RBP. Why not include it as well? That way, it will be
> > a complete support.
> 
> Hi Kirill, can you please share your thoughts?

I wrote the patch to handle redefined ReportFatalError() (the updated GHCI
comes soon). It doesn't need the RBP. And we run out of registers to stash
arguments into. Let's think about this when the first user of RBP comes up.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov