linux-kernel - Re: [RFC v2-fix-v2 1/3] x86/tdx: Handle port I/O in decompression code

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Date:   Tue, 8 Jun 2021 16:12:18 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Raj Ashok <ashok.raj@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC v2-fix-v2 1/3] x86/tdx: Handle port I/O in decompression code

On Tue, Jun 8, 2021 at 8:40 AM Kuppuswamy Sathyanarayanan
<sathyanarayanan.kuppuswamy@...ux.intel.com> wrote:
>
> Add support to replace in/out instructions in
> decompression code with TDX IO hypercalls.
>
> TDX cannot do port IO directly. The TDX module triggers
> a #VE exception to let the guest kernel to emulate port
> I/O, by converting them into TDX hypercalls to call the
> host.
>
> But for the really early code in the decompressor, #VE
> cannot be used because the IDT needed for handling the
> exception is not set-up, and some other infrastructure
> needed by the handler is missing. So to support port IO
> in decompressor code, directly replace in/out instructions
> with TDX IO hypercalls. This can beeasily achieved by
> modifying __in/__out macros.
>
> Also, since TDX IO hypercall requires an IO size parameter,
> modify __in/__out macros to accept size as input parameter.

Looks good to me:

Reviewed-by: Dan Williams <dan.j.williams@...el.com>