linux-kernel - [PATCH v3] of/fdt: Don't worry about non-memory region overlap for no-map

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Message-Id: <20211215195354.634746-1-swboyd@chromium.org>
Date:   Wed, 15 Dec 2021 11:53:54 -0800
From:   Stephen Boyd <swboyd@...omium.org>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        Mike Rapoport <rppt@...nel.org>,
        Douglas Anderson <dianders@...omium.org>,
        Nicolas Boichat <drinkcat@...omium.org>,
        Quentin Perret <qperret@...gle.com>,
        Jan Kiszka <jan.kiszka@...mens.com>
Subject: [PATCH v3] of/fdt: Don't worry about non-memory region overlap for no-map

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're in the reserved memory node. This if
condition will still trigger though if the DT has a /memreserve/ that
completely subsumes the no-map memory carveouts in the reserved memory
node. 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. If it isn't memory,
presumably it was removed from the memory map via /memreserve/ and thus
can't be mapped anyway.

This silences a warning seen at boot on sc7180-trogdor.dtsi boards that
have /memreserve/ populated by the bootloader where those reserved
regions overlap with the reserved-memory carveouts that we have in DT
for other purposes like communicating with remote processors.

For example in sc7180.dtsi we have the following reserved-memory
node:

	smem_mem: memory@...00000 {
		reg = <0x0 0x80900000 0x0 0x200000>;
		no-map;
	};

and the memreserve injected by the bootloader is

	/memreserve/ 0x80800000 0x400000;

so the reserved memory region overlaps with the no-map carveouts and we
get the following warning message printed at boot:

 OF: fdt: Reserved memory: failed to reserve memory for node 'memory@...00000': base 0x0000000080900000, size 2 MiB

Everything keeps working, just the no-map property is being ignored in
__reserved_mem_reserve_reg() because the region we're trying to avoid
mapping has already been removed from the memory via the memreserve.

Cc: Mike Rapoport <rppt@...nel.org>
Cc: Douglas Anderson <dianders@...omium.org>
Cc: Nicolas Boichat <drinkcat@...omium.org>
Cc: Quentin Perret <qperret@...gle.com>
Cc: Jan Kiszka <jan.kiszka@...mens.com>
Fixes: 8a5a75e5e9e5 ("of/fdt: Make sure no-map does not remove already reserved regions")
Signed-off-by: Stephen Boyd <swboyd@...omium.org>
---

Changes from v2 (https://lore.kernel.org/r/20211215072011.496998-1-swboyd@chromium.org):
 * More details in commit text

Changes from v1 (https://lore.kernel.org/r/20210520012731.3731314-1-swboyd@chromium.org):
 * 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(-)

diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
index bdca35284ceb..c736e5bcc2f6 100644
--- a/drivers/of/fdt.c
+++ b/drivers/of/fdt.c
@@ -482,9 +482,11 @@ static int __init early_init_dt_reserve_memory_arch(phys_addr_t base,
 	if (nomap) {
 		/*
 		 * If the memory is already reserved (by another region), we
-		 * should not allow it to be marked nomap.
+		 * should not allow it to be marked nomap, but don't worry
+		 * if the region isn't memory as it won't be mapped.
 		 */
-		if (memblock_is_region_reserved(base, size))
+		if (memblock_overlaps_region(&memblock.memory, base, size) &&
+		    memblock_is_region_reserved(base, size))
 			return -EBUSY;

 		return memblock_mark_nomap(base, size);

base-commit: 136057256686de39cc3a07c2e39ef6bc43003ff6
-- 
https://chromeos.dev