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

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Date:   Tue, 12 Sep 2023 00:57:01 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "Hansen, Dave" <dave.hansen@...el.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "bp@...en8.de" <bp@...en8.de>, "x86@...nel.org" <x86@...nel.org>,
        "hpa@...or.com" <hpa@...or.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "n.borisov.lkml@...il.com" <n.borisov.lkml@...il.com>
Subject: RE: [PATCH v4 00/12] Unify TDCALL/SEAMCALL and TDVMCALL assembly



> -----Original Message-----
> From: Huang, Kai <kai.huang@...el.com>
> Sent: Tuesday, September 12, 2023 10:30 AM
> To: kirill.shutemov@...ux.intel.com; peterz@...radead.org;
> pbonzini@...hat.com; linux-kernel@...r.kernel.org
> Cc: Hansen, Dave <dave.hansen@...el.com>; Christopherson,, Sean
> <seanjc@...gle.com>; bp@...en8.de; x86@...nel.org; hpa@...or.com;
> mingo@...hat.com; tglx@...utronix.de;
> sathyanarayanan.kuppuswamy@...ux.intel.com; Yamahata, Isaku
> <isaku.yamahata@...el.com>; n.borisov.lkml@...il.com
> Subject: Re: [PATCH v4 00/12] Unify TDCALL/SEAMCALL and TDVMCALL
> assembly
> 
> On Mon, 2023-09-11 at 19:08 +0200, Paolo Bonzini wrote:
> > On 8/15/23 13:01, 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.
> >
> > Not sure it if's new in this version but I'm seeing
> >
> >      WARNING: modpost: EXPORT symbol "__seamcall_ret" [vmlinux] version ...
> >      Is "__seamcall_ret" prototyped in <asm/asm-prototypes.h>?
> >      WARNING: modpost: EXPORT symbol "__seamcall" [vmlinux] version ...
> >      Is "__seamcall" prototyped in <asm/asm-prototypes.h>?
> >      WARNING: modpost: EXPORT symbol "__seamcall_saved_ret" [vmlinux]
> version ...
> >      Is "__seamcall_saved_ret" prototyped in <asm/asm-prototypes.h>?
> >
> > which is fixed by
> >
> > diff --git a/arch/x86/include/asm/asm-prototypes.h
> > b/arch/x86/include/asm/asm-prototypes.h
> > index 8f80de627c60..eff5252e9c86 100644
> > --- a/arch/x86/include/asm/asm-prototypes.h
> > +++ b/arch/x86/include/asm/asm-prototypes.h
> > @@ -6,6 +6,7 @@
> >   #include <asm/page.h>
> >   #include <asm/checksum.h>
> >   #include <asm/mce.h>
> > +#include <asm/tdx.h>
> >
> >   #include <asm-generic/asm-prototypes.h>
> >
> 
> Thanks Paolo!
> 
> I never met this issue, not even from LKP.  Do you happen to know which Kconfig
> option can trigger this?  Or would you mind sharing your .config?

(replying via outlook due to some networking issue of my home network)

After digging, this is due to exporting __seamcall*() assembly functions while MODVERSIONS is enabled.  

This series itself doesn't cause this warning.

I didn't export them in this series because I would like to leave to KVM patches when we are sure we need to export them.  

E.g., I have seamcall*() wrappers to retry running out of entropy, and we may have concern exporting __seamcall*() low level functions directly and may wish to export higher level wrappers.

So I think the fix should be with the patch that truly exports those __seamcall*().  I'll talk to Isaku on this to get his idea.

Thanks!