linux-kernel - Re: [PATCH 10/26] x86/tdx: Support TDX guest port I/O at decompression time

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Date:   Thu, 13 Jan 2022 14:51:54 +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: [PATCH 10/26] x86/tdx: Support TDX guest port I/O at
 decompression time

On Tue, Dec 14, 2021 at 06:02:48PM +0300, Kirill A. Shutemov wrote:
> From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
> 
> Port IO triggers a #VE exception in TDX guests.  During normal runtime,
> the kernel will handle those exceptions for any port IO.
> 
> But for the early code in the decompressor, #VE cannot be used because
> the IDT needed for handling the exception is not set up.
							  ... yet.

Well, we're setting up and IDT twice in

arch/x86/boot/compressed/idt_64.c

as early as startup_64 for SEV. And the second stage one
do_boot_stage2_vc() handles port IO too.

Can't you hook in your VE handler there too?

> Replace IN/OUT instructions with TDX IO hypercalls by defining helper
> macros __in/__out and by re-defining them in the decompressor code.
> Also, since TDX IO hypercall requires an IO size parameter, allow
> __in/__out macros to accept size as an input parameter.

Please end function/macro names with parentheses. I think in this
particular case you wanna say

"__in*()/__out*() macros"

When a function is mentioned in the changelog, either the text body or the
subject line, please use the format 'function_name()'. Omitting the
brackets after the function name can be ambiguous::

  Subject: subsys/component: Make reservation_count static

  reservation_count is only used in reservation_stats. Make it static.

The variant with brackets is more precise::

  Subject: subsys/component: Make reservation_count() static

  reservation_count() is only called from reservation_stats(). Make it
  static.

-- 
Regards/Gruss,
    Boris.

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