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

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Date:   Fri, 13 May 2022 11:01:43 +0200
From:   Borislav Petkov <bp@...e.de>
To:     Dionna Amalie Glaze <dionnaglaze@...gle.com>,
        Michael Roth <michael.roth@....com>
Cc:     Borislav Petkov <bp@...en8.de>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        "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>,
        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

+ mroth
- brijesh

On Thu, May 12, 2022 at 10:34:02PM -0700, Dionna Amalie Glaze wrote:
> Kirill, I've been tracking these changes to see if we can handle the
> unaccepted memory type for SEV-SNP, but testing has been an issue. The
> proposed patch in Ovmf to introduce unaccepted memory seems to have
> stalled out last September
> (https://www.mail-archive.com/devel@edk2.groups.io/msg35842.html) and
> is particularly difficult to adapt to SEV-SNP since it doesn't follow
> the TDVF way of initializing all memory. Is there a different
> development I might have missed so that we might test these cases?
> Without the UEFI introducing EFI_UNACCEPTED_MEMORY type, any kernel
> uses are essentially dead code.
> 
> Thanks,
> -Dionna
> 
> (apologies for repost in text mode)
> 
> On Tue, May 10, 2022 at 4:04 AM Borislav Petkov <bp@...en8.de> wrote:
> >
> > On Fri, May 06, 2022 at 06:30:13PM +0300, Kirill A. Shutemov wrote:
> > > I find it harder to follow.
> >
> > If in doubt, always consider using a helper function:
> >
> > ---
> >
> > diff --git a/arch/x86/boot/compressed/efi.h b/arch/x86/boot/compressed/efi.h
> > index 7db2f41b54cd..cf475243b6d5 100644
> > --- a/arch/x86/boot/compressed/efi.h
> > +++ b/arch/x86/boot/compressed/efi.h
> > @@ -32,6 +32,7 @@ typedef       struct {
> >  } efi_table_hdr_t;
> >
> >  #define EFI_CONVENTIONAL_MEMORY                 7
> > +#define EFI_UNACCEPTED_MEMORY          15
> >
> >  #define EFI_MEMORY_MORE_RELIABLE \
> >                                 ((u64)0x0000000000010000ULL)    /* higher reliability */
> > diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
> > index 28b91df9d31e..39bb4c319dfc 100644
> > --- a/arch/x86/boot/compressed/kaslr.c
> > +++ b/arch/x86/boot/compressed/kaslr.c
> > @@ -671,6 +671,23 @@ static bool process_mem_region(struct mem_vector *region,
> >  }
> >
> >  #ifdef CONFIG_EFI
> > +
> > +/*
> > + * Only EFI_CONVENTIONAL_MEMORY and EFI_UNACCEPTED_MEMORY (if supported) are guaranteed
> > + * to be free.
> > + */
> > +static inline bool memory_type_is_free(efi_memory_desc_t *md)
> > +{
> > +       if (md->type == EFI_CONVENTIONAL_MEMORY)
> > +               return true;
> > +
> > +       if (IS_ENABLED(CONFIG_UNACCEPTED_MEMORY))
> > +               if (md->type == EFI_UNACCEPTED_MEMORY)
> > +                       return true;
> > +
> > +       return false;
> > +}
> > +
> >  /*
> >   * Returns true if we processed the EFI memmap, which we prefer over the E820
> >   * table if it is available.
> > @@ -723,21 +740,9 @@ process_efi_entries(unsigned long minimum, unsigned long image_size)
> >                  * free memory and thus available to place the kernel image into,
> >                  * but in practice there's firmware where using that memory leads
> >                  * to crashes.
> > -                *
> > -                * Only EFI_CONVENTIONAL_MEMORY and EFI_UNACCEPTED_MEMORY (if
> > -                * supported) are guaranteed to be free.
> >                  */
> > -
> > -               switch (md->type) {
> > -               case EFI_CONVENTIONAL_MEMORY:
> > -                       break;
> > -               case EFI_UNACCEPTED_MEMORY:
> > -                       if (IS_ENABLED(CONFIG_UNACCEPTED_MEMORY))
> > -                               break;
> > +               if (!memory_type_is_free(md))
> >                         continue;
> > -               default:
> > -                       continue;
> > -               }
> >
> >                 if (efi_soft_reserve_enabled() &&
> >                     (md->attribute & EFI_MEMORY_SP))
> > --
> > Regards/Gruss,
> >     Boris.
> >
> > https://people.kernel.org/tglx/notes-about-netiquette
> 
> 
> 
> -- 
> -Dionna Glaze, PhD (she/her)
> 

-- 
Regards/Gruss,
    Boris.

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