• Juergen Gross's avatar
    x86/boot: Add ACPI RSDP address to setup_header · ae7e1238
    Juergen Gross authored
    Xen PVH guests receive the address of the RSDP table from Xen. In order
    to support booting a Xen PVH guest via Grub2 using the standard x86
    boot entry we need a way for Grub2 to pass the RSDP address to the
    kernel.
    
    For this purpose expand the struct setup_header to hold the physical
    address of the RSDP address. Being zero means it isn't specified and
    has to be located the legacy way (searching through low memory or
    EBDA).
    
    While documenting the new setup_header layout and protocol version
    2.14 add the missing documentation of protocol version 2.13.
    
    There are Grub2 versions in several distros with a downstream patch
    violating the boot protocol by writing past the end of setup_header.
    This requires another update of the boot protocol to enable the kernel
    to distinguish between a specified RSDP address and one filled with
    garbage by such a broken Grub2.
    
    From protocol 2.14 on Grub2 will write the version it is supporting
    (but never a higher value than found to be supported by the kernel)
    ored with 0x8000 to the version field of setup_header. This enables
    the kernel to know up to which field Grub2 has written information
    to. All fields after that are supposed to be clobbered.
    Signed-off-by: default avatarJuergen Gross <jgross@suse.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: boris.ostrovsky@oracle.com
    Cc: bp@alien8.de
    Cc: corbet@lwn.net
    Cc: linux-doc@vger.kernel.org
    Cc: xen-devel@lists.xenproject.org
    Link: http://lkml.kernel.org/r/20181010061456.22238-3-jgross@suse.comSigned-off-by: Ingo Molnar's avatarIngo Molnar <mingo@kernel.org>
    ae7e1238
bootparam.h 7.55 KB