linux-kernel - Re: [PATCH v12 20/22] x86/virt/tdx: Allow SEAMCALL to handle #UD and #GP

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Message-ID: <20230630090309.6mnsvfhcptekmzfu@box.shutemov.name>
Date:   Fri, 30 Jun 2023 12:03:09 +0300
From:   kirill.shutemov@...ux.intel.com
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Kai Huang <kai.huang@...el.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org,
        dave.hansen@...el.com, tony.luck@...el.com, tglx@...utronix.de,
        bp@...en8.de, mingo@...hat.com, hpa@...or.com, seanjc@...gle.com,
        pbonzini@...hat.com, david@...hat.com, dan.j.williams@...el.com,
        rafael.j.wysocki@...el.com, ashok.raj@...el.com,
        reinette.chatre@...el.com, len.brown@...el.com, ak@...ux.intel.com,
        isaku.yamahata@...el.com, ying.huang@...el.com, chao.gao@...el.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com, nik.borisov@...e.com,
        bagasdotme@...il.com, sagis@...gle.com, imammedo@...hat.com
Subject: Re: [PATCH v12 20/22] x86/virt/tdx: Allow SEAMCALL to handle #UD and
 #GP

On Wed, Jun 28, 2023 at 11:16:41PM +0200, Peter Zijlstra wrote:
> On Wed, Jun 28, 2023 at 11:11:32PM +0200, Peter Zijlstra wrote:
> > --- a/arch/x86/virt/vmx/tdx/tdxcall.S
> > +++ b/arch/x86/virt/vmx/tdx/tdxcall.S
> > @@ -17,37 +17,44 @@
> >   *            TDX module and hypercalls to the VMM.
> >   * SEAMCALL - used by TDX hosts to make requests to the
> >   *            TDX module.
> > + *
> > + *-------------------------------------------------------------------------
> > + * TDCALL/SEAMCALL ABI:
> > + *-------------------------------------------------------------------------
> > + * Input Registers:
> > + *
> > + * RAX                 - TDCALL Leaf number.
> > + * RCX,RDX,R8-R9       - TDCALL Leaf specific input registers.
> > + *
> > + * Output Registers:
> > + *
> > + * RAX                 - TDCALL instruction error code.
> > + * RCX,RDX,R8-R11      - TDCALL Leaf specific output registers.
> > + *
> > + *-------------------------------------------------------------------------
> > + *
> > + * __tdx_module_call() function ABI:
> > + *
> > + * @fn   (RDI)         - TDCALL Leaf ID,    moved to RAX
> > + * @regs (RSI)         - struct tdx_regs pointer
> > + *
> > + * Return status of TDCALL via RAX.
> >   */
> > +.macro TDX_MODULE_CALL host:req ret:req
> > +	FRAME_BEGIN
> >  
> > +	mov	%rdi, %rax
> > +	mov	$TDX_SEAMCALL_VMFAILINVALID, %rdi
> >  
> > +	mov	TDX_MODULE_rcx(%rsi), %rcx
> > +	mov	TDX_MODULE_rdx(%rsi), %rdx
> > +	mov	TDX_MODULE_r8(%rsi),  %r8
> > +	mov	TDX_MODULE_r9(%rsi),  %r9
> > +//	mov	TDX_MODULE_r10(%rsi), %r10
> > +//	mov	TDX_MODULE_r11(%rsi), %r11
> >  
> > +.if \host
> > +1:	seamcall
> >  	/*
> >  	 * SEAMCALL instruction is essentially a VMExit from VMX root
> >  	 * mode to SEAM VMX root mode.  VMfailInvalid (CF=1) indicates
> 	...
> >  	 * This value will never be used as actual SEAMCALL error code as
> >  	 * it is from the Reserved status code class.
> >  	 */
> > +	cmovc	%rdi, %rax
> >  2:
> > +.else
> >  	tdcall
> > +.endif
> >  
> > +.if \ret
> > +	movq %rcx, TDX_MODULE_rcx(%rsi)
> > +	movq %rdx, TDX_MODULE_rdx(%rsi)
> > +	movq %r8,  TDX_MODULE_r8(%rsi)
> > +	movq %r9,  TDX_MODULE_r9(%rsi)
> > +	movq %r10, TDX_MODULE_r10(%rsi)
> > +	movq %r11, TDX_MODULE_r11(%rsi)
> > +.endif
> > +
> > +	FRAME_END
> > +	RET
> > +
> > +.if \host
> > +3:
> > +	mov	$TDX_SW_ERROR, %rdi
> > +	or	%rdi, %rax
> > +	jmp 2b
> >  
> > +	_ASM_EXTABLE_FAULT(1b, 3b)
> > +.endif
> >  .endm
> 
> Isn't that much simpler?

I'm okay either way.

Obviously, arch/x86/coco/tdx/tdcall.S has to be patched to use the new
TDX_MODULE_CALL macro.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov