On Fri, 07 Jan 2022 11:42:32 -0800, Stephen Boyd wrote:
> In commit 8a5a75e5e9e5 ("of/fdt: Make sure no-map does not remove
> already reserved regions") we returned -EBUSY when trying to mark
> regions as no-map when they intersect with reserved memory. The goal was
> to find bad no-map reserved memory DT nodes that would unmap the kernel
> text/data sections.
>
> The problem is the reserved memory check will still trigger if the DT
> has a /memreserve/ that completely subsumes the no-map memory carveouts
> in the reserved memory node _and_ that region is also not part of the
> memory reg property. For example in sc7180.dtsi we have the following
> reserved-memory and memory node:
>
> memory@80000000 {
> /* We expect the bootloader to fill in the size */
> reg = <0 0x80000000 0 0>;
> };
>
> smem_mem: memory@80900000 {
> reg = <0x0 0x80900000 0x0 0x200000>;
> no-map;
> };
>
> and the memreserve filled in by the bootloader is
>
> /memreserve/ 0x80800000 0x400000;
>
> while the /memory node is transformed into
>
> memory@80000000 {
> /* The bootloader fills in the size, and adds another region */
> reg = <0 0x80000000 0 0x00800000>,
> <0 0x80c00000 0 0x7f200000>;
> };
>
> The smem region is doubly reserved via /memreserve/ and by not being
> part of the /memory reg property. This leads to the following warning
> printed at boot.
>
> OF: fdt: Reserved memory: failed to reserve memory for node 'memory@80900000': base 0x0000000080900000, size 2 MiB
>
> Otherwise nothing really goes wrong because the smem region is not going
> to be mapped by the kernel's direct linear mapping given that it isn't
> part of the memory node. Therefore, let's only consider this to be a
> problem if we're trying to mark a region as no-map and it is actually
> memory that we're intending to keep out of the kernel's direct mapping
> but it's already been reserved.
>
> Acked-by: Mike Rapoport <rppt@xxxxxxxxxx>
> Cc: Douglas Anderson <dianders@xxxxxxxxxxxx>
> Cc: Nicolas Boichat <drinkcat@xxxxxxxxxxxx>
> Cc: Quentin Perret <qperret@xxxxxxxxxx>
> Cc: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
> Fixes: 8a5a75e5e9e5 ("of/fdt: Make sure no-map does not remove already reserved regions")
> Signed-off-by: Stephen Boyd <swboyd@xxxxxxxxxxxx>
> ---
>
> Changes from v3 (https://lore.kernel.org/r/20211215195354.634746-1-swboyd@xxxxxxxxxxxx):
> * Even more details in commit text
>
> Changes from v2 (https://lore.kernel.org/r/20211215072011.496998-1-swboyd@xxxxxxxxxxxx):
> * More details in commit text
>
> Changes from v1 (https://lore.kernel.org/r/20210520012731.3731314-1-swboyd@xxxxxxxxxxxx):
> * Use memblock_overlaps_region instead of memblock_is_region_memory()
> * Add more details to commit text
>
> drivers/of/fdt.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
Applied, thanks!
