linux-kernel - Re: [PATCHv2 1/7] mm: Add support for unaccepted memory

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Message-ID: <Yd/Xy+L61YewxE21@kernel.org>
Date:   Thu, 13 Jan 2022 09:42:03 +0200
From:   Mike Rapoport <rppt@...nel.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     "Kirill A. Shutemov" <kirill@...temov.name>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        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>, x86@...nel.org,
        linux-mm@...ck.org, linux-coco@...ts.linux.dev,
        linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2 1/7] mm: Add support for unaccepted memory

On Wed, Jan 12, 2022 at 10:40:53AM -0800, Dave Hansen wrote:
> On 1/12/22 10:30, Kirill A. Shutemov wrote:
> > On Tue, Jan 11, 2022 at 11:46:37AM -0800, Dave Hansen wrote:
> > > > diff --git a/mm/memblock.c b/mm/memblock.c
> > > > index 1018e50566f3..6dfa594192de 100644
> > > > --- a/mm/memblock.c
> > > > +++ b/mm/memblock.c
> > > > @@ -1400,6 +1400,7 @@ phys_addr_t __init memblock_alloc_range_nid(phys_addr_t size,
> > > >    		 */
> > > >    		kmemleak_alloc_phys(found, size, 0, 0);
> > > > +	accept_memory(found, found + size);
> > > >    	return found;
> > > >    }
> > > 
> > > This could use a comment.
> > 
> > How about this:
> > 
> > 	/*
> > 	 * Some Virtual Machine platforms, such as Intel TDX or AMD SEV-SNP,
> > 	 * requiring memory to be accepted before it can be used by the
> > 	 * guest.
> > 	 *
> > 	 * Accept the memory of the allocated buffer.
> > 	 */
> 
> I think a one-liner that might cue the reader to go look at accept_memory()
> itself would be fine.  Maybe:
> 
> 	/* Make the memblock usable when running in picky VM guests: */

I'd s/memblock/found range/ or something like that, memblock is too vague
IMO
 
> That implies that the memory isn't usable without doing this and also points
> out that it's related to running in a guest.

-- 
Sincerely yours,
Mike.