Re: [PATCH 4/5] x86/boot/64: Explicitly map boot_params and command line

Joerg Roedel
2020-10-08T09:48:40Z

On Wed, Oct 07, 2020 at 03:53:50PM -0400, Arvind Sankar wrote:
> This is fragile, as boot_params and the command line mappings are
> required for the main kernel. If EARLY_PRINTK and RANDOMIZE_BASE are
> disabled, a QEMU/OVMF boot never accesses the command line in the
> decompressor stub, and so it never gets mapped. The main kernel accesses
> it from the identity mapping if AMD_MEM_ENCRYPT is enabled, and will
> crash.

Looked again, and I think that is wrong for boot_params, which are
touched unconditionally at the beginning of extract_kernel().

For the cmdline you are right, but one of CONFIG_ACPI,
CONFIG_RANDOMIZE_BASE, CONFIG_X86_5LEVEL or CONFIG_EARLY_PRINTK is
sufficient to have it touched during this boot stage.

Regards,

Joerg