Date:   Fri, 7 Jan 2022 14:46:41 +0100
From:   Borislav Petkov <bp@alien8.de>
To:     "Kirill A. Shutemov" <kirill@shutemov.name>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        tglx@linutronix.de, mingo@redhat.com, dave.hansen@intel.com,
        luto@kernel.org, peterz@infradead.org,
        sathyanarayanan.kuppuswamy@linux.intel.com, aarcange@redhat.com,
        ak@linux.intel.com, dan.j.williams@intel.com, david@redhat.com,
        hpa@zytor.com, jgross@suse.com, jmattson@google.com,
        joro@8bytes.org, jpoimboe@redhat.com, knsathya@kernel.org,
        pbonzini@redhat.com, sdeep@vmware.com, seanjc@google.com,
        tony.luck@intel.com, vkuznets@redhat.com, wanpengli@tencent.com,
        x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 08/26] x86/tdx: Handle in-kernel MMIO
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References: <20211214150304.62613-1-kirill.shutemov@linux.intel.com>
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On Wed, Jan 05, 2022 at 06:43:11PM +0300, Kirill A. Shutemov wrote:
> Not encrypted, saved/restored by TDX module. But yes, cannot be exposed
> (without guest intend).
> 
> I talk here about *why* the traditional way to handle MMIO -- on VMM side
> -- doesn't work for TDX. It's not safe with untrusted VMM.

Lemme see if I understand this correctly: TDX module saves/restores
guest registers so a malicious hypervisor cannot access them? And that's
why you can't do the traditional way MMIO is done?

> readX()/writeX() helpers limit the range of instructions which can trigger
> MMIO. It makes MMIO instruction emulation feasible. Raw access to MMIO
> region allows compiler to generate whatever instruction it wants.
> Supporting all possible instructions is a task of a different scope.

Yap, please add that to the commit message.

Thx.

-- 
Regards/Gruss,
    Boris.

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