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Message-ID: <CAMj1kXF_B1ggD8zdKn_hyzgaa1zMhL+ygXRJaWhhrStqWPn9vw@mail.gmail.com>
Date: Wed, 22 Sep 2021 09:14:46 +0200
From: Ard Biesheuvel <ardb@...nel.org>
To: Geert Uytterhoeven <geert+renesas@...der.be>
Cc: Russell King <linux@...linux.org.uk>,
Nicolas Pitre <nico@...xnic.net>,
Linus Walleij <linus.walleij@...aro.org>,
Lukasz Stelmach <l.stelmach@...sung.com>,
Simon Horman <horms@...ge.net.au>,
Linux ARM <linux-arm-kernel@...ts.infradead.org>,
"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
<devicetree@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
kexec@...ts.infradead.org
Subject: Re: [PATCH v6] ARM: uncompress: Parse "linux,usable-memory-range" DT property
On Wed, 15 Sept 2021 at 15:20, Geert Uytterhoeven
<geert+renesas@...der.be> wrote:
>
> Add support for parsing the "linux,usable-memory-range" DT property.
> This property is used to describe the usable memory reserved for the
> crash dump kernel, and thus makes the memory reservation explicit.
> If present, Linux no longer needs to mask the program counter, and rely
> on the "mem=" kernel parameter to obtain the start and size of usable
> memory.
>
> For backwards compatibility, the traditional method to derive the start
> of memory is still used if "linux,usable-memory-range" is absent.
>
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
Acked-by: Ard Biesheuvel <ardb@...nel.org>
> ---
> KernelVersion: v5.15-rc1
> ---
> The corresponding patch for kexec-tools is "[PATCH] arm: kdump: Add DT
> properties to crash dump kernel's DTB", which is still valid:
> https://lore.kernel.org/r/20200902154129.6358-1-geert+renesas@glider.be/
>
> v6:
> - All dependencies are in v5.15-rc1,
>
> v5:
> - Remove the addition of "linux,elfcorehdr" and
> "linux,usable-memory-range" handling to arch/arm/mm/init.c,
>
> v4:
> - Remove references to architectures in chosen.txt, to avoid having to
> change this again when more architectures copy kdump support,
> - Remove the architecture-specific code for parsing
> "linux,usable-memory-range" and "linux,elfcorehdr", as the FDT core
> code now takes care of this,
> - Move chosen.txt change to patch changing the FDT core,
> - Use IS_ENABLED(CONFIG_CRASH_DUMP) instead of #ifdef,
>
> v3:
> - Rebase on top of accepted solution for DTB memory information
> handling, which is part of v5.12-rc1,
>
> v2:
> - Rebase on top of reworked DTB memory information handling.
> ---
> .../arm/boot/compressed/fdt_check_mem_start.c | 48 ++++++++++++++++---
> 1 file changed, 42 insertions(+), 6 deletions(-)
>
> diff --git a/arch/arm/boot/compressed/fdt_check_mem_start.c b/arch/arm/boot/compressed/fdt_check_mem_start.c
> index 62450d824c3ca180..9291a2661bdfe57f 100644
> --- a/arch/arm/boot/compressed/fdt_check_mem_start.c
> +++ b/arch/arm/boot/compressed/fdt_check_mem_start.c
> @@ -55,16 +55,17 @@ static uint64_t get_val(const fdt32_t *cells, uint32_t ncells)
> * DTB, and, if out-of-range, replace it by the real start address.
> * To preserve backwards compatibility (systems reserving a block of memory
> * at the start of physical memory, kdump, ...), the traditional method is
> - * always used if it yields a valid address.
> + * used if it yields a valid address, unless the "linux,usable-memory-range"
> + * property is present.
> *
> * Return value: start address of physical memory to use
> */
> uint32_t fdt_check_mem_start(uint32_t mem_start, const void *fdt)
> {
> - uint32_t addr_cells, size_cells, base;
> + uint32_t addr_cells, size_cells, usable_base, base;
> uint32_t fdt_mem_start = 0xffffffff;
> - const fdt32_t *reg, *endp;
> - uint64_t size, end;
> + const fdt32_t *usable, *reg, *endp;
> + uint64_t size, usable_end, end;
> const char *type;
> int offset, len;
>
> @@ -80,6 +81,27 @@ uint32_t fdt_check_mem_start(uint32_t mem_start, const void *fdt)
> if (addr_cells > 2 || size_cells > 2)
> return mem_start;
>
> + /*
> + * Usable memory in case of a crash dump kernel
> + * This property describes a limitation: memory within this range is
> + * only valid when also described through another mechanism
> + */
> + usable = get_prop(fdt, "/chosen", "linux,usable-memory-range",
> + (addr_cells + size_cells) * sizeof(fdt32_t));
> + if (usable) {
> + size = get_val(usable + addr_cells, size_cells);
> + if (!size)
> + return mem_start;
> +
> + if (addr_cells > 1 && fdt32_ld(usable)) {
> + /* Outside 32-bit address space */
> + return mem_start;
> + }
> +
> + usable_base = fdt32_ld(usable + addr_cells - 1);
> + usable_end = usable_base + size;
> + }
> +
> /* Walk all memory nodes and regions */
> for (offset = fdt_next_node(fdt, -1, NULL); offset >= 0;
> offset = fdt_next_node(fdt, offset, NULL)) {
> @@ -107,7 +129,20 @@ uint32_t fdt_check_mem_start(uint32_t mem_start, const void *fdt)
>
> base = fdt32_ld(reg + addr_cells - 1);
> end = base + size;
> - if (mem_start >= base && mem_start < end) {
> + if (usable) {
> + /*
> + * Clip to usable range, which takes precedence
> + * over mem_start
> + */
> + if (base < usable_base)
> + base = usable_base;
> +
> + if (end > usable_end)
> + end = usable_end;
> +
> + if (end <= base)
> + continue;
> + } else if (mem_start >= base && mem_start < end) {
> /* Calculated address is valid, use it */
> return mem_start;
> }
> @@ -123,7 +158,8 @@ uint32_t fdt_check_mem_start(uint32_t mem_start, const void *fdt)
> }
>
> /*
> - * The calculated address is not usable.
> + * The calculated address is not usable, or was overridden by the
> + * "linux,usable-memory-range" property.
> * Use the lowest usable physical memory address from the DTB instead,
> * and make sure this is a multiple of 2 MiB for phys/virt patching.
> */
> --
> 2.25.1
>
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