linux-kernel - Re: [PATCHv2 03/29] x86/tdx: Add __tdx_module_call() and __tdx

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Date:   Fri, 4 Feb 2022 16:20:23 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Kai Huang <kai.huang@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...el.com, luto@...nel.org,
        peterz@...radead.org, sathyanarayanan.kuppuswamy@...ux.intel.com,
        aarcange@...hat.com, ak@...ux.intel.com, dan.j.williams@...el.com,
        david@...hat.com, hpa@...or.com, jgross@...e.com,
        jmattson@...gle.com, joro@...tes.org, jpoimboe@...hat.com,
        knsathya@...nel.org, pbonzini@...hat.com, sdeep@...are.com,
        seanjc@...gle.com, tony.luck@...el.com, vkuznets@...hat.com,
        wanpengli@...cent.com, x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2 03/29] x86/tdx: Add __tdx_module_call() and
 __tdx_hypercall() helper functions

On Fri, Feb 04, 2022 at 10:51:38PM +1300, Kai Huang wrote:
> > +	.if \host
> > +	seamcall
> > +	/*
> > +	 * SEAMCALL instruction is essentially a VMExit from VMX root
> > +	 * mode to SEAM VMX root mode.  VMfailInvalid (CF=1) indicates
> > +	 * that the targeted SEAM firmware is not loaded or disabled,
> > +	 * or P-SEAMLDR is busy with another SEAMCALL.  %rax is not
> > +	 * changed in this case.
> > +	 *
> > +	 * Set %rax to TDX_SEAMCALL_VMFAILINVALID for VMfailInvalid.
> > +	 * This value will never be used as actual SEAMCALL error code.
> > +	 */
> > +	jnc     .Lno_vmfailinvalid
> > +	mov     $TDX_SEAMCALL_VMFAILINVALID, %rax
> > +	jmp     .Lno_output_struct
> 
> If I read correctly, in case of VMfailInvalid, another "pop %r12" is needed
> before jmp to .Lno_output_struct, otherwise it doesn't match the stack (pushed
> twice).

Oopsie. Thanks for catching it.

> However, since "test %rax, %rax" will also catch TDX_SEAMCALL_VMFAILINVALID, it
> seems we can just delete above "jmp .Lno_output_struct"?

Good point. Will do it this way.

-- 
 Kirill A. Shutemov