linux-kernel - Re: [PATCH v2 07/11] x86/tdx: Make TDX_HYPERCALL asm similar to TDX_MODULE

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Date:   Fri, 21 Jul 2023 11:06:47 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "peterz@...radead.org" <peterz@...radead.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>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.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>,
        "n.borisov.lkml@...il.com" <n.borisov.lkml@...il.com>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Subject: Re: [PATCH v2 07/11] x86/tdx: Make TDX_HYPERCALL asm similar to
 TDX_MODULE_CALL

On Fri, 2023-07-21 at 10:01 +0200, Peter Zijlstra wrote:
> On Fri, Jul 21, 2023 at 05:19:30AM +0000, Huang, Kai wrote:
> 
> > Sorry I got a build regression from lkp:
> > 
> > vmlinux.o: warning: objtool: __halt+0x3a: call to __tdx_hypercall() leaves
> > .noinstr.text section
> 
> Clearly you should enable CONFIG_DEBUG_ENTRY in your own development
> .config ;-)

Ah thanks a lot!

I've been investigating how to reproduce at my own environment this afternoon!

LKP people are not aware of what triggered this check either.  I'll pass to
them.

> 
> > The reason is __halt() is annotated with "__cpuidle", but it calls
> > __tdx_hypercall(), which is now a normal C function, w/o
> > instrumentation_begin()/end().
> > 
> > I think we can annotate __tdx_hypercall() as 'noinstr' too and keep
> > __tdx_hypercall_failed() unchanged.  Anyway in the upstream code,
> > __tdx_hypercall() is in '.noinstr.text'.
> > 
> > diff --git a/arch/x86/coco/tdx/tdx-shared.c b/arch/x86/coco/tdx/tdx-shared.c
> > index 13139ee171c8..b47c8cce91b0 100644
> > --- a/arch/x86/coco/tdx/tdx-shared.c
> > +++ b/arch/x86/coco/tdx/tdx-shared.c
> > @@ -70,7 +70,7 @@ bool tdx_accept_memory(phys_addr_t start, phys_addr_t end)
> >         return true;
> >  }
> >  
> > -u64 __tdx_hypercall(struct tdx_hypercall_args *args)
> > +noinstr u64 __tdx_hypercall(struct tdx_hypercall_args *args)
> >  {
> >         struct tdx_module_args margs = {
> >                 .rcx = TDVMCALL_EXPOSE_REGS_MASK,
> > diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
> > index aba58484ba10..f10b0e512a36 100644
> > --- a/arch/x86/coco/tdx/tdx.c
> > +++ b/arch/x86/coco/tdx/tdx.c
> > @@ -37,8 +37,9 @@
> >  
> >  #define TDREPORT_SUBTYPE_0     0
> >  
> > -void __tdx_hypercall_failed(void)
> > +noinstr void __tdx_hypercall_failed(void)
> >  {
> > +       instrumentation_begin();
> >         panic("TDVMCALL failed. TDX module bug?");
> >  }
> > 
> > 
> > We can fold this to this patch.
> > 
> > Do you have any comments?
> 
> Yes this is fine, we violate noinstr for WARN etc.. There's no point
> being pendantic about these things if we're going to take the machine
> down anyway.

Thanks.  I'll fold above to this patch and sent out a v3 (given that it seems
you also want a patch to adjust the layout of 'struct tdx_module_args' for
TDH.VP.ENTER).