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

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Message-ID: <20230721080155.GB3630545@hirez.programming.kicks-ass.net>
Date:   Fri, 21 Jul 2023 10:01:55 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Huang, Kai" <kai.huang@...el.com>
Cc:     "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "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>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "n.borisov.lkml@...il.com" <n.borisov.lkml@...il.com>,
        "Yamahata, Isaku" <isaku.yamahata@...el.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, 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 ;-)

> 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.