linux-kernel - Re: [PATCHv2 07/29] x86/tdx: Handle CPUID via #VE

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Date:   Tue, 01 Feb 2022 22:39:35 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...el.com,
        luto@...nel.org, peterz@...radead.org
Cc:     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,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCHv2 07/29] x86/tdx: Handle CPUID via #VE

On Mon, Jan 24 2022 at 18:01, Kirill A. Shutemov wrote:
> +static bool tdx_handle_cpuid(struct pt_regs *regs)
> +{
> +	struct tdx_hypercall_output out;
> +
> +	/*
> +	 * Emulate the CPUID instruction via a hypercall. More info about
> +	 * ABI can be found in TDX Guest-Host-Communication Interface
> +	 * (GHCI), section titled "VP.VMCALL<Instruction.CPUID>".
> +	 */
> +	if (_tdx_hypercall(EXIT_REASON_CPUID, regs->ax, regs->cx, 0, 0, &out))
> +		return false;
> +
> +	/*
> +	 * As per TDX GHCI CPUID ABI, r12-r15 registers contain contents of
> +	 * EAX, EBX, ECX, EDX registers after the CPUID instruction execution.
> +	 * So copy the register contents back to pt_regs.
> +	 */
> +	regs->ax = out.r12;
> +	regs->bx = out.r13;
> +	regs->cx = out.r14;
> +	regs->dx = out.r15;
> +
> +	return true;
> +}

Ack.

>  bool tdx_get_ve_info(struct ve_info *ve)
>  {
>  	struct tdx_module_output out;
> @@ -157,8 +182,18 @@ bool tdx_get_ve_info(struct ve_info *ve)
>   */
>  static bool tdx_virt_exception_user(struct pt_regs *regs, struct ve_info *ve)
>  {
> -	pr_warn("Unexpected #VE: %lld\n", ve->exit_reason);
> -	return false;
> +	bool ret = false;
> +
> +	switch (ve->exit_reason) {
> +	case EXIT_REASON_CPUID:
> +		ret = tdx_handle_cpuid(regs);
> +		break;

Comment about ret and break applies accordingly.

Thanks,

        tglx