linux-kernel - Re: [PATCHv2 14/29] x86/tdx: Early boot handling of port I/O

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Date:   Wed, 2 Feb 2022 11:09:37 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     tglx@...utronix.de, mingo@...hat.com, 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 14/29] x86/tdx: Early boot handling of port I/O

On Mon, Jan 24, 2022 at 06:02:00PM +0300, Kirill A. Shutemov wrote:
> Subject: Re: [PATCHv2 14/29] x86/tdx: Early boot handling of port I/O

The condensed patch description in the subject line should start with a
uppercase letter and should be written in imperative tone:

	... Handle early boot port I/O

or so.

> From: Andi Kleen <ak@...ux.intel.com>
> 
> TDX guests cannot do port I/O directly. The TDX module triggers a #VE
> exception to let the guest kernel emulate port I/O, by converting them

s/,//

> into TDCALLs to call the host.
> 
> But before IDT handlers are set up, port I/O cannot be emulated using
> normal kernel #VE handlers. To support the #VE-based emulation during
> this boot window, add a minimal early #VE handler support in early
> exception handlers. This is similar to what AMD SEV does. This is
> mainly to support earlyprintk's serial driver, as well as potentially
> the VGA driver (although it is expected not to be used).

expectations, shmexpectations...

...

> diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
> index 1cb6346ec3d1..76d298ddfe75 100644
> --- a/arch/x86/kernel/head64.c
> +++ b/arch/x86/kernel/head64.c
> @@ -417,6 +417,9 @@ void __init do_early_exception(struct pt_regs *regs, int trapnr)
>  	    trapnr == X86_TRAP_VC && handle_vc_boot_ghcb(regs))
>  		return;
>  


	if (IS_ENABLED(CONFIG_INTEL_TDX_GUEST)) &&

> +	if (trapnr == X86_TRAP_VE && tdx_early_handle_ve(regs))
> +		return;
> +
>  	early_fixup_exception(regs, trapnr);

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette