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

Dionna Amalie Glaze
2022-05-13T05:34:20Z

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@alien8.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)