On 01/19/16 at 02:01pm, Mark Rutland wrote: > On Tue, Jan 19, 2016 at 09:45:53PM +0800, Dave Young wrote: > > 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: > > > > > >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. > > Other than for testing purposes, I don't see why you'd pass the kdump > kernel a DTB inconsistent with that the 1st kernel was passsed (other > than some proerties under /chosen). > > We added /sys/firmware/fdt specifically to allow the kexec tools to get > the exact DTB the first kernel used. There's no reason for tools to have > to make something up. Agreed, but kexec-tools has an option to pass in any dtb files. Who knows how one will use it unless dropping the option and use /sys/firmware/fdt unconditionally. If we choose to implement kexec_file_load only in kernel, the interfaces provided are kernel, initrd and cmdline. We can always use same dtb. > > > > > 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.. > > When booted via EFI, yes. > > For NUMA topology in !ACPI kernels, we might need to also retain and > parse memory nodes, but only for toplogy information. The kernel would > still only use memory as described by the EFI memory map. > > There's a horrible edge case I've spotted if performing a chain of > cross-endian kexecs: LE -> BE -> LE, as the BE kernel would have to > respect the EFI memory map so as to avoid corrupting it for the > subsequent LE kernel. Other than this I believe everything should just > work. Firmware do not know kernel endianniess, kernel should respect firmware maps and adapt to it, it sounds like a generic issue not specfic to kexec. > > > > 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. > > Sure. This is what I believe we should expose with an additional > property under /chosen, while keeping everything else pristine. > > The crash kernel can then limit itself to that region, while it would > have the information of the full memory map (which it could log and/or > use to drive other dumping). In this way kernel should be aware it is a kdump booting, it is doable though I feel it is better for kdump kernel in a black box with infomations it can use just like the 1st kernel. Things here is where we choose to cook the memory infomation in boot loader or in kernel itself. > > > Is it possible to modify uefi memmap for kdump case? > > Technically it would be possible, however I don't think it's necessary, > and I think it would be disadvantageous to do so. > > Describing the range(s) the crash kernel can use in separate properties > under /chosen has a number of advantages. Ok, I got the points. We have a is_kdump_kernel() by checking if there is elfcorehdr_addr kernel cmdline. This is mainly for some drivers which do not work well in kdump kernel some uncertain reasons. But ideally I think kernel should handle things just like in 1st kernel and avoid to use it. > > > > 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? > > We'd have a (slightly) modified DTB that contained additional properties > describing the range(s) reserved for use by the crash kernel. > > Other than those properties under /chosen (e.g. the command line, initrd > pointers if any), it would be the original DTB. > > Thanks, > Mark. Thanks Dave
