Re: [PATCH v2 1/3] x86/efi: Add BGRT image preservation during boot

["Marek Marczykowski-Górecki" <marmarek@invisiblethingslab.com>]

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On Fri, Mar 06, 2026 at 06:59:33PM +0530, Soumyajyotii Ssarkar wrote:
> The ACPI BGRT (Boot Graphics Resource Table) contains a pointer to a
> boot logo image stored in BootServicesData memory. When Xen reclaims
> this memory during boot, the image is lost and the BGRT table becomes
> invalid, causing Linux dom0 to report ACPI checksum errors.
> 
> Add preservation logic similar to ESRT table handling:
> - Locate BGRT table via XSDT during EFI boot services phase
> - Validate BMP image signature and size (max 16 MB)
> - Copy image to EfiACPIReclaimMemory (safe from reclamation)
> - Update BGRT table with new image address
> - Recalculate ACPI table checksum
> 
> The preservation runs automatically during efi_exit_boot() before
> Boot Services are terminated. This ensures the image remains
> accessible to dom0.
> 
> Open-coded ACPI parsing is used because Xen's ACPI subsystem is not
> available during the EFI boot phase. The RSDP is obtained from the
> EFI System Table, and the XSDT is walked manually to find BGRT.
> 
> Signed-off-by: Soumyajyotii Ssarkar <soumyajyotisarkar23@gmail.com>
> ---
>  xen/arch/x86/efi/efi-boot.h |   2 +
>  xen/common/efi/boot.c       | 187 ++++++++++++++++++++++++++++++++++++
>  2 files changed, 189 insertions(+)
> 
> diff --git a/xen/arch/x86/efi/efi-boot.h b/xen/arch/x86/efi/efi-boot.h
> index 42a2c46b5e..27792a56ff 100644
> --- a/xen/arch/x86/efi/efi-boot.h
> +++ b/xen/arch/x86/efi/efi-boot.h
> @@ -910,6 +910,8 @@ void __init efi_multiboot2(EFI_HANDLE ImageHandle,
> 
>      efi_relocate_esrt(SystemTable);
> 
> +    efi_preserve_bgrt_img(SystemTable);
> +

See my remark on v1 - efi_start() wants this change too.

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab

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