linux-kernel - [PATCH v4] of: fdt: Scan /memreserve/ last

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Date:   Mon, 24 Apr 2023 12:38:46 +0100
From:   Lucas Tanure <tanure@...ux.com>
To:     Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Mike Rapoport <rppt@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, jbrunet@...libre.com,
        linux-amlogic@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org,
        martin.blumenstingl@...glemail.com, narmstrong@...libre.com,
        stefan@...er.ch, Lucas Tanure <tanure@...ux.com>
Subject: [PATCH v4] of: fdt: Scan /memreserve/ last

Change the scanning /memreserve/ and /reserved-memory node order to fix
Kernel panic on Khadas Vim3 Board.

If /memreserve/ goes first, the memory is reserved, but nomap can't be
applied to the region. So the memory won't be used by Linux, but it is
still present in the linear map as normal memory, which allows
speculation. Legitimate access to adjacent pages will cause the CPU
to end up prefetching into them leading to Kernel panic.

So /reserved-memory node should go first, as it has a more updated
description of the memory regions and can apply flags, like nomap.

Signed-off-by: Lucas Tanure <tanure@...ux.com>i
---
Previous Threads:
#regzbot link: https://lore.kernel.org/linux-arm-kernel/40ca11f84b7cdbfb9ad2ddd480cb204a@agner.ch/#regzbot
#regzbot link: https://lore.kernel.org/all/CAJX_Q+1Tjc+-TjZ6JW9X0NxEdFe=82a9626yL63j7uVD4LpxEA@mail.gmail.com/

V1: https://lore.kernel.org/all/20230406151429.524591-1-tanure@linux.com/
v2: https://lore.kernel.org/all/20230410120017.41664-1-tanure@linux.com/
v3: https://lore.kernel.org/linux-mm/20230412224620.8909-1-tanure@linux.com/T/

Change from V3:
 - Drop cover letter
 - Add more information into the patch

Change from V2:
 - Remove region overlap and reserved checks

Change from V1:
 - Instead of allowing to mark nomap a region already reserved, give
precedence to /reserved-memory node scan.
---
 drivers/of/fdt.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
index d14735a81301..bf502ba8da95 100644
--- a/drivers/of/fdt.c
+++ b/drivers/of/fdt.c
@@ -635,6 +635,9 @@ void __init early_init_fdt_scan_reserved_mem(void)
 	if (!initial_boot_params)
 		return;
 
+	fdt_scan_reserved_mem();
+	fdt_reserve_elfcorehdr();
+
 	/* Process header /memreserve/ fields */
 	for (n = 0; ; n++) {
 		fdt_get_mem_rsv(initial_boot_params, n, &base, &size);
@@ -643,8 +646,6 @@ void __init early_init_fdt_scan_reserved_mem(void)
 		memblock_reserve(base, size);
 	}
 
-	fdt_scan_reserved_mem();
-	fdt_reserve_elfcorehdr();
 	fdt_init_reserved_mem();
 }
 
-- 
2.40.0