On 01/18/16 at 07:26pm, AKASHI Takahiro wrote: > On 01/16/2016 05:16 AM, Mark Rutland wrote: > >On Fri, Jan 15, 2016 at 07:18:38PM +0000, Geoff Levand wrote: > >>From: AKASHI Takahiro <takahiro.akashi at linaro.org> > >> > >>This patch adds arch specific descriptions about kdump usage on arm64 > >>to kdump.txt. > >> > >>Signed-off-by: AKASHI Takahiro <takahiro.akashi at linaro.org> > >>--- > >> Documentation/kdump/kdump.txt | 23 ++++++++++++++++++++++- > >> 1 file changed, 22 insertions(+), 1 deletion(-) > >> > >>diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt > >>index bc4bd5a..36cf978 100644 > >>--- a/Documentation/kdump/kdump.txt > >>+++ b/Documentation/kdump/kdump.txt > >>@@ -18,7 +18,7 @@ memory image to a dump file on the local disk, or across the network to > >> a remote system. > >> > >> Kdump and kexec are currently supported on the x86, x86_64, ppc64, ia64, > >>-s390x and arm architectures. > >>+s390x, arm and arm64 architectures. > >> > >> When the system kernel boots, it reserves a small section of memory for > >> the dump-capture kernel. This ensures that ongoing Direct Memory Access > >>@@ -249,6 +249,20 @@ Dump-capture kernel config options (Arch Dependent, arm) > >> > >> AUTO_ZRELADDR=y > >> > >>+Dump-capture kernel config options (Arch Dependent, arm64) > >>+---------------------------------------------------------- > >>+ > >>+1) The maximum memory size on the dump-capture kernel must be limited by > >>+ specifying: > >>+ > >>+ mem=X[MG] > >>+ > >>+ where X should be less than or equal to the size in "crashkernel=" > >>+ boot parameter. Kexec-tools will automatically add this. > > > > > >This is extremely fragile, and will trivially fail when the kernel can > >be loaded anywhere (see [1]). > > As I said before, this restriction also exists on arm, but I understand > that recent Ard's patches break it. > > >We must explicitly describe the set of regions the crash kernel may use > >(i.e. we need base and size). NAK in the absence of that. > > There seem to exist several approaches: > (a) use a device-tree property, "linux,usable-memory", in addition to "reg" > under "memory" node > (b) use a kernel's early parameter, "memmap=nn[@#$]ss" > > Power PC takes (a), while this does not work on efi-started kernel > because dtb has no "memory" nodes under efi. > X86 takes (b). If we take this, we will need to overwrite a weak > early_init_dt_add_memory(). X86 takes another way in latest kexec-tools and kexec_file_load, that is recreating E820 table and pass it to kexec/kdump kernel, if the entries are over E820 limitation then turn to use setup_data list for remain entries. I think it is X86 specific. Personally I think device tree property is better. Thanks Dave
