arm64: Unhash early pointer print plus improve comment

When facing a really early issue on DT parsing we have currently
a message that shows both the physical and virtual address of the FDT.
The printk pointer modifier for the virtual address shows a hashed
address there unless the user provides "no_hash_pointers" parameter in
the command-line. The situation in which this message shows-up is a bit
more serious though: the boot process is broken, nothing can be done
(even an oops is too much for this early stage) so we have this message
as a last resort in order to help debug bootloader issues, for example.
Hence, we hereby change that to "%px" in order to make debugging easy,
there's not much information leak risk in such early boot failure.

Also, we tried to improve a bit the commenting on that function, given
that if kernel fails there, it just hangs forever in a cpu_relax() loop.
The reason we cannot BUG/panic is that is too early to do so; thanks to
Mark Brown for pointing that on IRC and thanks Robin Murphy for the good
pointer hash discussion in the mailing-list.

Cc: Mark Brown <broonie@kernel.org>
Cc: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20211221155230.1532850-1-gpiccoli@igalia.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
index be5f85b..a804305 100644 (file)
--- a/arch/arm64/kernel/setup.c
+++ b/arch/arm64/kernel/setup.c
@@ -189,11 +189,16 @@ static void __init setup_machine_fdt(phys_addr_t dt_phys)
 
        if (!dt_virt || !early_init_dt_scan(dt_virt)) {
                pr_crit("\n"
-                       "Error: invalid device tree blob at physical address %pa (virtual address 0x%p)\n"
+                       "Error: invalid device tree blob at physical address %pa (virtual address 0x%px)\n"
                        "The dtb must be 8-byte aligned and must not exceed 2 MB in size\n"
                        "\nPlease check your bootloader.",
                        &dt_phys, dt_virt);
 
+               /*
+                * Note that in this _really_ early stage we cannot even BUG()
+                * or oops, so the least terrible thing to do is cpu_relax(),
+                * or else we could end-up printing non-initialized data, etc.
+                */
                while (true)
                        cpu_relax();
        }