On 01/19/16 at 12:51pm, Mark Rutland wrote: > On Tue, Jan 19, 2016 at 08:28:48PM +0800, Dave Young wrote: > > On 01/19/16 at 02:35pm, AKASHI Takahiro wrote: > > > On 01/19/2016 10:43 AM, Dave Young wrote: > > > >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. > > > > > > Thanks. I will visit x86 code again. > > > > > > >I think it is X86 specific. Personally I think device tree property is > > > >better. > > > > > > Do you think so? > > > > I'm not sure it is the best way. For X86 we run into problem with > > memmap= design, one example is pci domain X (X>1) need the pci memory > > ranges being passed to kdump kernel. When we passed reserved ranges in /proc/iomem > > to 2nd kernel we find that cmdline[] array is not big enough. > > I'm not sure how PCI ranges relate to the memory map used for normal > memory (i.e. RAM), though I'm probably missing some caveat with the way > ACPI and UEFI describe PCI. Why does memmap= affect PCI memory? Here is the old patch which was rejected in kexec-tools: http://lists.infradead.org/pipermail/kexec/2013-February/007924.html > > If the kernel got the rest of its system topology from DT, the PCI > regions would be described there. Yes, if kdump kernel use same DT as 1st kernel. > > > Do you think for arm64 only usable memory is necessary to let kdump kernel > > know? I'm curious about how arm64 kernel get all memory layout from boot loader, > > via UEFI memmap? > > When booted via EFI, we use the EFI memory map. The EFI stub handles > acquring the relevant information and passing that to the first kernel > in the DTB (see Documentation/arm/uefi.txt). Ok, thanks for the pointer. So in dt we are just have uefi memmap infomation instead of memory nodes details.. > > A kexec'd kernel should simply inherit that. So long as the DTB and/or > UEFI tables in memory are the same, it would be the same as a cold boot. For kexec all memory ranges are same, for kdump we need use original reserved range with crashkernel= as usable memory and all other orignal usable ranges are not usable anymore. Is it possible to modify uefi memmap for kdump case? > > In the !EFI case, we use the memory nodes in the DTB. Only in this case > could usable-memory properties in memory nodes make sense. I'd prefer a > uniform property under /chosen for both cases. We stil use same DTB, need to modify the DT and update the usable and unusable nodes for kdump? > Thanks, > Mark. Thanks Dave
