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

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Date:   Thu, 12 May 2022 22:34:02 -0700
From:   Dionna Amalie Glaze <dionnaglaze@...gle.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     "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>,
        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

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)