linux-kernel - Re: [PATCH v2 5/6] platform/x86: intel_tdx_attest: Add TDX Guest attestation interface driver

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Message-ID: <ce0feeec-a949-35f8-3010-b0d69acbbc2e@linux.intel.com>
Date:   Thu, 8 Jul 2021 17:38:41 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     Dave Hansen <dave.hansen@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Mark Gross <mgross@...ux.intel.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>
Cc:     Peter H Anvin <hpa@...or.com>, Tony Luck <tony.luck@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        platform-driver-x86@...r.kernel.org, bpf@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH v2 5/6] platform/x86: intel_tdx_attest: Add TDX Guest
 attestation interface driver


> Expensive and permanently fractures the direct map.
>
> I'm struggling to figure out why the direct map is even touched here.
I think Sathya did it this way because the TD interface requires a 
physical address.
> Why not just use a vmalloc area mapping?  You really just need *a*
> decrypted mapping to the page.  You don't need to make *every* mapping
> to the page decrypted.

Yes it would be possible to use vmap() on the page and only set the vmap 
encrypted by passing the right flags directly.

That would avoid breaking up the direct mapping.


-Andi