[PATCH v2] ARM: decompress: Use /memreserve/ DTS nodes when validating memory

If the bootloader needs the start of memory to be preserved, for example
because it dropped the Trusted Firmware blob there, this chunk of memory
shouldn't be used by the kernel.

To avoid adding yet another SoC-specific text offset to arch/arm/Makefile,
this patch allows for a /memreserve/ entry in the DTS to mark off the
memory chunk instead.

Signed-off-by: Bert Vermeulen <redacted>
---
 arch/arm/boot/compressed/fdt_check_mem_start.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/arch/arm/boot/compressed/fdt_check_mem_start.c b/arch/arm/boot/compressed/fdt_check_mem_start.c
index 62450d824c3c..1d47de1e860b 100644
--- a/arch/arm/boot/compressed/fdt_check_mem_start.c
+++ b/arch/arm/boot/compressed/fdt_check_mem_start.c

@@ -64,7 +64,7 @@ uint32_t fdt_check_mem_start(uint32_t mem_start, const void *fdt)
 	uint32_t addr_cells, size_cells, base;
 	uint32_t fdt_mem_start = 0xffffffff;
 	const fdt32_t *reg, *endp;
-	uint64_t size, end;
+	uint64_t rsvaddr, size, end;
 	const char *type;
 	int offset, len;
 

@@ -74,6 +74,19 @@ uint32_t fdt_check_mem_start(uint32_t mem_start, const void *fdt)
 	if (fdt_magic(fdt) != FDT_MAGIC)
 		return mem_start;
 
+	for (offset = fdt_off_mem_rsvmap(fdt); ; offset += 16) {
+		rsvaddr = get_val(fdt + offset, 2);
+		size = get_val(fdt + offset + 8, 2);
+
+		if (!rsvaddr && !size)
+			break;
+
+		end = rsvaddr + size;
+		if (mem_start >= rsvaddr && mem_start <= end)
+			/* Relocate past reserved block */
+			mem_start = round_up(end, SZ_2M);
+	}
+
 	/* There may be multiple cells on LPAE platforms */
 	addr_cells = get_cells(fdt, "#address-cells");
 	size_cells = get_cells(fdt, "#size-cells");

-- 
2.25.1


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On Tue, Sep 7, 2021 at 4:57 PM Bert Vermeulen [off-list ref] wrote:

If the bootloader needs the start of memory to be preserved, for example
because it dropped the Trusted Firmware blob there, this chunk of memory
shouldn't be used by the kernel.

To avoid adding yet another SoC-specific text offset to arch/arm/Makefile,
this patch allows for a /memreserve/ entry in the DTS to mark off the
memory chunk instead.

Signed-off-by: Bert Vermeulen <redacted>

Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

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On Tue, 7 Sept 2021 at 16:57, Bert Vermeulen [off-list ref] wrote:

If the bootloader needs the start of memory to be preserved, for example
because it dropped the Trusted Firmware blob there, this chunk of memory
shouldn't be used by the kernel.

To avoid adding yet another SoC-specific text offset to arch/arm/Makefile,
this patch allows for a /memreserve/ entry in the DTS to mark off the
memory chunk instead.

Signed-off-by: Bert Vermeulen <redacted>

Thanks for working on this - I hope this will allow us to phase out at
least some of the existing text_offset hacks too.

Acked-by: Ard Biesheuvel <ardb@kernel.org>

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