Re: [PATCH v3 2/3] xen/efi: Support loading initrd using GRUB2 LoadFile2 protocol

[Jan Beulich <jbeulich@xxxxxxxx>]

On 25.06.2025 09:34, Frediano Ziglio wrote:
> --- a/xen/common/efi/boot.c
> +++ b/xen/common/efi/boot.c
> @@ -850,6 +850,74 @@ static bool __init read_file(EFI_FILE_HANDLE dir_handle, 
> CHAR16 *name,
>      return true;
>  }
>  
> +#pragma pack(1)
> +typedef struct {
> +    VENDOR_DEVICE_PATH              VenMediaNode;
> +    EFI_DEVICE_PATH                 EndNode;
> +} SINGLE_NODE_VENDOR_MEDIA_DEVPATH;
> +#pragma pack()

Where is this coming from? And why is this declared locally here, but the ...

> +static bool __init initrd_load_file2(const CHAR16 *name, struct file *file)
> +{
> +    static const SINGLE_NODE_VENDOR_MEDIA_DEVPATH __initconst 
> initrd_dev_path = {
> +        {
> +            {
> +                MEDIA_DEVICE_PATH, MEDIA_VENDOR_DP, { sizeof 
> (VENDOR_DEVICE_PATH) }
> +            },
> +            LINUX_EFI_INITRD_MEDIA_GUID
> +        },
> +        {
> +            END_DEVICE_PATH_TYPE, END_ENTIRE_DEVICE_PATH_SUBTYPE,
> +            { sizeof (EFI_DEVICE_PATH) }
> +        }
> +    };
> +    static EFI_GUID __initdata lf2_proto_guid = EFI_LOAD_FILE2_PROTOCOL_GUID;

... corresponding GUID is put in a (random?) header file?

> +    EFI_DEVICE_PATH *dp;
> +    EFI_LOAD_FILE2_PROTOCOL *lf2;
> +    EFI_HANDLE handle;
> +    EFI_STATUS ret;
> +    UINTN size;
> +
> +    dp = (EFI_DEVICE_PATH *)&initrd_dev_path;

Instead of a (fragile) cast, why not

    dp = &initrd_dev_path->VenMediaNode.Header;

? And then perhaps also as initializer of the variable?

> +    ret = efi_bs->LocateDevicePath(&lf2_proto_guid, &dp, &handle);
> +    if ( EFI_ERROR(ret) )
> +    {
> +        if ( ret == EFI_NOT_FOUND)
> +            return false;
> +        PrintErrMesg(L"Error getting file with LoadFile2 interface", ret);
> +    }
> +
> +    ret = efi_bs->HandleProtocol(handle, &lf2_proto_guid, (void **)&lf2);
> +    if ( EFI_ERROR(ret) )
> +        PrintErrMesg(L"LoadFile2 file does not provide correct protocol", 
> ret);
> +
> +    size = 0;
> +    ret = lf2->LoadFile(lf2, dp, false, &size, NULL);
> +    if ( ret != EFI_BUFFER_TOO_SMALL )
> +        PrintErrMesg(L"Loading failed", ret);

Here it's particularly bad, but throughout: How would one know in what
context the failure was? Wouldn't you want to include "name" in the
output? read_file() does include this detail.

> +    file->addr = min(1UL << (32 + PAGE_SHIFT),
> +                     HYPERVISOR_VIRT_END - DIRECTMAP_VIRT_START);

I understand you took this from read_file(), but the construct looks
outdated. For one, it should have been abstracted away when the Arm64
work was done (I don't think such a restriction exists there), and
then I'm also not sure the restriction would unconditionally apply on
x86 anymore.

> +    ret = efi_bs->AllocatePages(AllocateMaxAddress, EfiLoaderData,
> +                                PFN_UP(size), &file->addr);
> +    if ( EFI_ERROR(ret) )
> +        PrintErrMesg(L"Allocation failed", ret);
> +
> +    file->need_to_free = true;
> +    file->size = size;
> +
> +    ret = lf2->LoadFile(lf2, dp, false, &size, file->str);
> +    if ( EFI_ERROR(ret) )
> +    {
> +        efi_bs->FreePages(file->addr, PFN_UP(size));
> +        PrintErrMesg(L"Loading failed", ret);
> +    }
> +
> +    efi_arch_handle_module(file, name, NULL);

Shouldn't it be handle_file_info() that you call, and a little earlier?

> --- a/xen/include/efi/efidevp.h
> +++ b/xen/include/efi/efidevp.h
> @@ -398,5 +398,26 @@ typedef union {
>  
>  } EFI_DEV_PATH_PTR;
>  
> +#define EFI_LOAD_FILE2_PROTOCOL_GUID \
> +    { 0x4006c0c1, 0xfcb3, 0x403e, {0x99, 0x6d, 0x4a, 0x6c, 0x87, 0x24, 0xe0, 
> 0x6d } }
> +
> +typedef struct EFI_LOAD_FILE2_PROTOCOL EFI_LOAD_FILE2_PROTOCOL;
> +
> +typedef
> +EFI_STATUS
> +(EFIAPI *EFI_LOAD_FILE2)(
> +    IN EFI_LOAD_FILE2_PROTOCOL      *This,
> +    IN EFI_DEVICE_PATH              *FilePath,
> +    IN BOOLEAN                      BootPolicy,
> +    IN OUT UINTN                    *BufferSize,
> +    IN VOID                         *Buffer OPTIONAL
> +    );
> +
> +struct EFI_LOAD_FILE2_PROTOCOL {
> +    EFI_LOAD_FILE2                  LoadFile;
> +};
> +
> +#define LINUX_EFI_INITRD_MEDIA_GUID \
> +    { 0x5568e427, 0x68fc, 0x4f3d, {0xac, 0x74, 0xca, 0x55, 0x52, 0x31, 0xcc, 
> 0x68} }
>  
>  #endif

While I'm not maintainer of this code anymore, I hope the new maintainers will
still respect the original idea of keeping these headers in sync with their
origin. The way it's arranged, this change doesn't look like it would have been
taken from the gnu-efi package (albeit I will admit I didn't go check).

Jan