linux-kernel - Re: [PATCHv5 06/12] x86/boot/compressed: Handle unaccepted memory

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Date:   Fri, 6 May 2022 18:30:13 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Borislav Petkov <bp@...en8.de>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        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>,
        Dave Hansen <dave.hansen@...el.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Mike Rapoport <rppt@...nel.org>,
        David Hildenbrand <david@...hat.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: [PATCHv5 06/12] x86/boot/compressed: Handle unaccepted memory

On Tue, May 03, 2022 at 04:12:55PM +0200, Borislav Petkov wrote:
> On Mon, Apr 25, 2022 at 06:39:28AM +0300, Kirill A. Shutemov wrote:
> > diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
> > index 411b268bc0a2..59db90626042 100644
> > --- a/arch/x86/boot/compressed/kaslr.c
> > +++ b/arch/x86/boot/compressed/kaslr.c
> > @@ -725,10 +725,20 @@ process_efi_entries(unsigned long minimum, unsigned long image_size)
> >  		 * but in practice there's firmware where using that memory leads
> >  		 * to crashes.
> >  		 *
> > -		 * Only EFI_CONVENTIONAL_MEMORY is guaranteed to be free.
> > +		 * Only EFI_CONVENTIONAL_MEMORY and EFI_UNACCEPTED_MEMORY (if
> > +		 * supported) are guaranteed to be free.
> >  		 */
> > -		if (md->type != EFI_CONVENTIONAL_MEMORY)
> > +
> > +		switch (md->type) {
> > +		case EFI_CONVENTIONAL_MEMORY:
> > +			break;
> > +		case EFI_UNACCEPTED_MEMORY:
> > +			if (IS_ENABLED(CONFIG_UNACCEPTED_MEMORY))
> > +				break;
> >  			continue;
> > +		default:
> > +			continue;
> > +		}
> 
> Is there any special reason for this to be a switch-case or can it
> simply be a compound conditional if (bla...) ?

The equivalent 'if' statement is something like:

		if (md->type != EFI_CONVENTIONAL_MEMORY &&
		    !(md->type == EFI_UNACCEPTED_MEMORY && IS_ENABLED(CONFIG_UNACCEPTED_MEMORY)))
		    continue;

I find it harder to follow.

Do you want me to change to the 'if' anyway?

-- 
 Kirill A. Shutemov