On Wed, 15 Sept 2021 at 15:20, Geert Uytterhoeven <geert+renesas@xxxxxxxxx> 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@xxxxxxxxx> Acked-by: Ard Biesheuvel <ardb@xxxxxxxxxx> > --- > 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@xxxxxxxxx/ > > 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 >
