linux-kernel - Re: [RFC v2 26/32] x86/mm: Move force_dma

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Date:   Wed, 26 May 2021 21:46:08 -0700
From:   "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Dave Hansen <dave.hansen@...el.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dan Williams <dan.j.williams@...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@...r.kernel.org
Subject: Re: [RFC v2 26/32] x86/mm: Move force_dma_unencrypted() to common
 code



On 5/17/21 6:28 PM, Kuppuswamy, Sathyanarayanan wrote:
>> Because the code is already separate.  You're actually going to some
>> trouble to move the SEV-specific code and then combine it with the
>> TDX-specific code.
>>
>> Anyway, please just give it a shot.  Should take all of ten minutes.  If
>> it doesn't work out in practice, fine.  You'll have a good paragraph for
>> the changelog.
> 
> After reviewing the code again, I have noticed that we don't really have
> much common code between AMD and TDX. So I don't see any justification for
> creating this common layer. So, I have decided to drop this patch and move
> Intel TDX specific memory encryption init code to patch titled "[RFC v2 30/32]
> x86/tdx: Make DMA pages shared". This model is similar to how AMD-SEV
> does the initialization.
> 
> I have sent the modified patch as reply to patch titled "[RFC v2 30/32]
> x86/tdx: Make DMA pages shared". Please check and let me know your comment

My method of using separate initialization file for Intel only code will not
work if we want to support both AMD SEV and TDX guest support in same binary.
So please ignore my previous reply. I will address the issue as per your
original comments and send you an updated patch.

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer