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Message-ID: <20210714145308.GC2441138@robh.at.kernel.org>
Date: Wed, 14 Jul 2021 08:53:08 -0600
From: Rob Herring <robh@...nel.org>
To: Geert Uytterhoeven <geert+renesas@...der.be>
Cc: Russell King <linux@...linux.org.uk>,
Nicolas Pitre <nico@...xnic.net>,
Ard Biesheuvel <ardb@...nel.org>,
Linus Walleij <linus.walleij@...aro.org>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Nick Kossifidis <mick@....forth.gr>,
Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>,
Albert Ou <aou@...s.berkeley.edu>,
Frank Rowand <frowand.list@...il.com>,
Dave Young <dyoung@...hat.com>,
Mike Rapoport <rppt@...nel.org>, Baoquan He <bhe@...hat.com>,
Vivek Goyal <vgoyal@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
linux-riscv@...ts.infradead.org, kexec@...ts.infradead.org,
linux-mm@...ck.org, linux-renesas-soc@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 10/10] ARM: Parse kdump DT properties
On Wed, Jul 14, 2021 at 02:50:20PM +0200, Geert Uytterhoeven wrote:
> Parse the following DT properties in the crash dump kernel, to provide a
> modern interface between kexec and the crash dump kernel:
> - linux,elfcorehdr: ELF core header segment, similar to the
> "elfcorehdr=" kernel parameter.
> - linux,usable-memory-range: Usable memory reserved for the crash dump
> kernel.
> This 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, and
> the "elfcorehdr=" and "mem=" kernel parameters are still parsed.
>
> Loosely based on the ARM64 version by Akashi Takahiro.
>
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> ---
> 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/linux-arm-kernel/20200902154129.6358-1-geert+renesas@glider.be/
>
> 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 ++++++++++++++++---
> arch/arm/mm/init.c | 30 ++++++++++++
> 2 files changed, 72 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.
> */
> diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
> index 6162a070a4104a26..dfaee199554dda97 100644
> --- a/arch/arm/mm/init.c
> +++ b/arch/arm/mm/init.c
> @@ -4,6 +4,7 @@
> *
> * Copyright (C) 1995-2005 Russell King
> */
> +#include <linux/crash_dump.h>
> #include <linux/kernel.h>
> #include <linux/errno.h>
> #include <linux/swap.h>
> @@ -221,8 +222,35 @@ void check_cpu_icache_size(int cpuid)
> }
> #endif
>
> +/*
> + * reserve_elfcorehdr() - reserves memory for elf core header
> + *
> + * This function reserves the memory occupied by an elf core header
> + * described in the device tree. This region contains all the
> + * information about primary kernel's core image and is used by a dump
> + * capture kernel to access the system memory on primary kernel.
> + */
> +static void __init reserve_elfcorehdr(void)
> +{
> + if (!IS_ENABLED(CONFIG_CRASH_DUMP) || !elfcorehdr_size)
> + return;
> +
> + if (memblock_is_region_reserved(elfcorehdr_addr, elfcorehdr_size)) {
> + pr_warn("elfcorehdr is overlapped\n");
> + return;
> + }
> +
> + memblock_reserve(elfcorehdr_addr, elfcorehdr_size);
Can't this be in common code?
> +
> + pr_info("Reserving %llu KiB of memory at 0x%llx for elfcorehdr\n",
> + elfcorehdr_size >> 10, elfcorehdr_addr);
> +}
> +
> void __init arm_memblock_init(const struct machine_desc *mdesc)
> {
> + /* Handle linux,usable-memory-range property */
> + memblock_cap_memory_range(cap_mem_addr, cap_mem_size);
> +
> /* Register the kernel text, kernel data and initrd with memblock. */
> memblock_reserve(__pa(KERNEL_START), KERNEL_END - KERNEL_START);
>
> @@ -236,6 +264,8 @@ void __init arm_memblock_init(const struct machine_desc *mdesc)
>
> early_init_fdt_scan_reserved_mem();
>
> + reserve_elfcorehdr();
> +
> /* reserve memory for DMA contiguous allocations */
> dma_contiguous_reserve(arm_dma_limit);
>
> --
> 2.25.1
>
>
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