On Mon, Aug 22, 2016 at 02:47:30PM +0100, James Morse wrote: > On 22/08/16 02:29, AKASHI Takahiro wrote: > > On Fri, Aug 19, 2016 at 04:52:17PM +0530, Pratyush Anand wrote: > >> It will help kexec-tools to prevent copying of any unnecessary data. I > >> think, then you also need to change phys_offset calculation in kexec-tools. That > >> should be start of either of first "reserved" or "System RAM" block. > > > > Good point, but I'm not sure this is always true. > > > Is there any system whose ACPI memory is *not* part of DRAM > > From the spec, it looks like this is allowed. > > What do you mean by 'DRAM'? Any ACPI region will be in the UEFI memory map, so > the question is what is its type and memory attributes? Yes. > The UEFI spec[0] says ACPI regions can have a type of EfiACPIReclaimMemory or > EfiACPIMemoryNVS, the memory attributes aren't specified, so are chosen by the > firmware. > > It is possible these regions have to be mapped non-cacheable, page 40 has a > couple of: > > If no information about the table location exists in the UEFI memory map or > ACPI memory > > descriptors, the table is assumed to be non-cached. > > reserve_regions() in drivers/firmware/efi/arm-init.c will add any entry in the > memory map that has a 'WB' attribute to the memblock.memory list (via > early_init_dt_add_memory_arch()), it will also mark as no-map regions that have > this attribute and aren't in the is_reserve_region() list. > > If these ACPI regions have the 'WB' attribute, we add them as memory and mark > them nomap. These show up as either a hole, or 'reserved' in /proc/iomem. > If they don't have the 'WB' attribute, then then they are left out of memblock > and aren't part of DRAM, I don't think these will show up in /proc/iomem at all. Let's say, 0x1000-0x1fff: reserved (SRAM for UEFI, WB) 0x80000000-0xffffffff: System RAM (DRAM) If, as Pratyush suggested, "reserved" resources are added to phys_offset calculation, the kernel linear mapping area starts at PAGE_OFFSET, but there is no actual mapping around PAGE_OFFSET. It won't hurt anything, but looks funny. So we'd better not include "reserved" in phys_offset calculation anyway. -> Pratyush Thanks, -Takahiro AKASHI > > > Thanks, > > James > > [0] '2.3.6 AArch64 Platforms' of version 2.6 of the UEFI spec at > http://uefi.org/specifications