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Subject: Re: [RFC v2 26/32] x86/mm: Move force_dma_unencrypted() to common
 code
To:     Dave Hansen <dave.hansen@intel.com>,
        "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        Sean Christopherson <seanjc@google.com>
Cc:     "Kirill A. Shutemov" <kirill@shutemov.name>,
        Peter Zijlstra <peterz@infradead.org>,
        Andy Lutomirski <luto@kernel.org>,
        Dan Williams <dan.j.williams@intel.com>,
        Tony Luck <tony.luck@intel.com>,
        Kirill Shutemov <kirill.shutemov@linux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@kernel.org>,
        Raj Ashok <ashok.raj@intel.com>, linux-kernel@vger.kernel.org
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From:   Andi Kleen <ak@linux.intel.com>
Message-ID: <a72bce3a-d7da-c595-9456-cfda42d9cdc3@linux.intel.com>
Date:   Thu, 13 May 2021 12:38:50 -0700
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On 5/13/2021 10:49 AM, Dave Hansen wrote:
> On 5/13/21 9:40 AM, Kuppuswamy, Sathyanarayanan wrote:
>> +#define PROTECTED_GUEST_BITMAP_LEN    128
>> +
>> +/* Protected Guest vendor types */
>> +#define GUEST_TYPE_TDX            (1)
>> +#define GUEST_TYPE_SEV            (2)
>> +
>> +/* Protected Guest features */
>> +#define MEMORY_ENCRYPTION        (20)
> I was assuming we'd reuse the X86_FEATURE infrastructure somehow.  Is
> there a good reason not to?


This for generic code. Would be a gigantic lift and lots of refactoring 
to move that out.

>
> That gives us all the compile-time optimization (via
> en/disabled-features.h) and static branches for "free".

There's no user so far which is anywhere near performance critical, so 
that would be total overkil

BTW right now I'm not even sure we need the bitmap for anything, but I 
guess it doesn't hurt.

-Andi