linux-kernel - Re: [PATCH v19 078/130] KVM: TDX: Implement TDX vcpu enter/exit path

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Date: Thu, 4 Apr 2024 21:51:30 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
	"Yamahata, Isaku" <isaku.yamahata@...el.com>
CC: "Zhang, Tina" <tina.zhang@...el.com>, "seanjc@...gle.com"
	<seanjc@...gle.com>, "Yuan, Hang" <hang.yuan@...el.com>, "Chen, Bo2"
	<chen.bo@...el.com>, "sagis@...gle.com" <sagis@...gle.com>,
	"isaku.yamahata@...il.com" <isaku.yamahata@...il.com>, "Aktas, Erdem"
	<erdemaktas@...gle.com>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v19 078/130] KVM: TDX: Implement TDX vcpu enter/exit path

On Thu, 2024-04-04 at 16:22 +0300, Kirill A. Shutemov wrote:
> On Mon, Feb 26, 2024 at 12:26:20AM -0800, isaku.yamahata@...el.com wrote:
> > @@ -491,6 +494,87 @@ void tdx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
> >  	 */
> >  }
> >  
> > +static noinstr void tdx_vcpu_enter_exit(struct vcpu_tdx *tdx)
> > +{
> 
> ...
> 
> > +	tdx->exit_reason.full = __seamcall_saved_ret(TDH_VP_ENTER, &args);
> 
> Call to __seamcall_saved_ret() leaves noinstr section.
> 
> __seamcall_saved_ret() has to be moved:
> 
> diff --git a/arch/x86/virt/vmx/tdx/seamcall.S b/arch/x86/virt/vmx/tdx/seamcall.S
> index e32cf82ed47e..6b434ab12db6 100644
> --- a/arch/x86/virt/vmx/tdx/seamcall.S
> +++ b/arch/x86/virt/vmx/tdx/seamcall.S
> @@ -44,6 +44,8 @@ SYM_FUNC_START(__seamcall_ret)
>  SYM_FUNC_END(__seamcall_ret)
>  EXPORT_SYMBOL_GPL(__seamcall_ret);
>  
> +.section .noinstr.text, "ax"
> +
>  /*
>   * __seamcall_saved_ret() - Host-side interface functions to SEAM software
>   * (the P-SEAMLDR or the TDX module), with saving output registers to the

Alternatively, I think we can explicitly use instrumentation_begin()/end()
around __seamcall_saved_ret() here.

__seamcall_saved_ret() could be used in the future for new SEAMCALLs (e.g.,
TDH.MEM.IMPORT) for TDX guest live migration.  And for that I don't think the
caller(s) is/are tagged with noinstr.