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

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Message-ID: <YJv6EWJmDYQL4Eqt@google.com>
Date:   Wed, 12 May 2021 15:53:53 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     "Kirill A. Shutemov" <kirill@...temov.name>,
        "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        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>, linux-kernel@...r.kernel.org
Subject: Re: [RFC v2 26/32] x86/mm: Move force_dma_unencrypted() to common
 code

On Wed, May 12, 2021, Dave Hansen wrote:
> On 5/12/21 6:08 AM, Kirill A. Shutemov wrote:
> >> That's not an excuse to have a bunch of AMD (or Intel) feature-specific
> >> code in a file named "common".  I'd make an attempt to keep them
> >> separate and then call into the two separate functions *from* the common
> >> function.
> > But why? What good does the additional level of inderection brings?
> > 
> > It's like saying arch/x86/kernel/cpu/common.c shouldn't have anything AMD
> > or Intel specific. If a function can cover both vendors I don't see a
> > point for additinal complexity.
> 
> 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.

Or maybe wait to see how Boris' propose protected_guest_has() pans out?  E.g. if
we can do "protected_guest_has(MEMORY_ENCRYPTION)" or whatever, then the truly
common bits could be placed into common.c without any vendor-specific logic.