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Subject: Re: [PATCH v2 5/6] platform/x86: intel_tdx_attest: Add TDX Guest
 attestation interface driver
To:     Andi Kleen <ak@linux.intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Hans de Goede <hdegoede@redhat.com>,
        Mark Gross <mgross@linux.intel.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>
Cc:     Peter H Anvin <hpa@zytor.com>, Tony Luck <tony.luck@intel.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Kirill Shutemov <kirill.shutemov@linux.intel.com>,
        Sean Christopherson <seanjc@google.com>,
        Kuppuswamy Sathyanarayanan <knsathya@kernel.org>,
        x86@kernel.org, linux-kernel@vger.kernel.org,
        platform-driver-x86@vger.kernel.org, bpf@vger.kernel.org,
        netdev@vger.kernel.org
References: <20210707204249.3046665-1-sathyanarayanan.kuppuswamy@linux.intel.com>
 <20210707204249.3046665-6-sathyanarayanan.kuppuswamy@linux.intel.com>
 <06c85c19-e16c-3121-ed47-075cfa779b67@kernel.org>
 <169451ef-e8f6-5a07-f47a-61eaa085b4ef@intel.com>
 <ce0feeec-a949-35f8-3010-b0d69acbbc2e@linux.intel.com>
From:   "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@linux.intel.com>
Message-ID: <afba42c2-e925-d937-8893-80f995a143b4@linux.intel.com>
Date:   Mon, 12 Jul 2021 17:33:25 -0700
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Hi Dave,

On 7/8/21 5:38 PM, Andi Kleen wrote:
>> 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.

Is it alright to have non coherent mappings? If yes, any documentation reference for it?

> 
> That would avoid breaking up the direct mapping.

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer