linux-kernel - Re: [PATCHv7 14/14] x86/tdx: Add unaccepted memory support

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Date:   Mon, 27 Jun 2022 13:42:11 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Borislav Petkov <bp@...en8.de>, Andy Lutomirski <luto@...nel.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Joerg Roedel <jroedel@...e.de>,
        Ard Biesheuvel <ardb@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Tom Lendacky <thomas.lendacky@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Varad Gautam <varad.gautam@...e.com>,
        Dario Faggioli <dfaggioli@...e.com>,
        Mike Rapoport <rppt@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        marcelo.cerri@...onical.com, tim.gardner@...onical.com,
        khalid.elmously@...onical.com, philip.cox@...onical.com,
        x86@...nel.org, linux-mm@...ck.org, linux-coco@...ts.linux.dev,
        linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv7 14/14] x86/tdx: Add unaccepted memory support

On Fri, Jun 24, 2022 at 09:22:03AM -0700, Dave Hansen wrote:
> On 6/14/22 05:02, Kirill A. Shutemov wrote:
> >  static inline void __accept_memory(phys_addr_t start, phys_addr_t end)
> >  {
> >  	/* Platform-specific memory-acceptance call goes here */
> > -	error("Cannot accept memory");
> > +	if (is_tdx_guest())
> > +		tdx_accept_memory(start, end);
> > +	else
> > +		error("Cannot accept memory: unknown platform\n");
> >  }
> 
> There are quite a few of these
> 
> 	if (tdx())
> 		...
> 
> conditions in common code here.  Shouldn't this be something like a
> CC_ATTR_MEM_ACCEPT?
> 
> 	if (cc_platform_has(CC_ATTR_MEM_ACCEPT))
> 		cc_accept_memory(...);
> 	else
> 		error("Cannot accept memory: unknown platform\n");
> 
> I understand that TDX is the first one to the party.  Is this the time
> to add the cc_ infrastructure?

We need if tdx() check *somewhere* as how exactly memory gets accepted is
specific to a particular platform.

There are two callsites where memory acceptance happens. One of them is in
boot stub where we don't have cc_ infrastructure. So it will boil down to
a single cc_accept_memory() that will have 'if tdx()' inside.

I don't see much sense in the exercise. We can as well keep the 'if' in
accept_memory().

-- 
 Kirill A. Shutemov