When sme enabled on AMD server, we also need to support kdump. Because the memory is encrypted in the first kernel, we will remap the old memory encrypted to the second kernel(crash kernel), and sme is also enabled in the second kernel, otherwise the old memory encrypted can not be decrypted. Because simply changing the value of a C-bit on a page will not automatically encrypt the existing contents of a page, and any data in the page prior to the C-bit modification will become unintelligible. A page of memory that is marked encrypted will be automatically decrypted when read from DRAM and will be automatically encrypted when written to DRAM.
For the kdump, it is necessary to distinguish whether the memory is encrypted. Furthermore, we should also know which part of the memory is encrypted or decrypted. We will appropriately remap the memory according to the specific situation in order to tell cpu how to deal with the data(encrypted or decrypted). For example, when sme enabled, if the old memory is encrypted, we will remap the old memory in encrypted way, which will automatically decrypt the old memory encrypted when we read those data from the remapping address. ---------------------------------------------- | first-kernel | second-kernel | kdump support | | (mem_encrypt=on|off) | (yes|no) | |--------------+---------------+---------------| | on | on | yes | | off | off | yes | | on | off | no | | off | on | no | |______________|_______________|_______________| This patch is only for SME kdump, it is not support SEV kdump. For kdump(SME), there are two cases that doesn't support: 1. SME is enabled in the first kernel, but SME is disabled in the second kernel Because the old memory is encrypted, we can't decrypt the old memory if SME is off in the second kernel. 2. SME is disabled in the first kernel, but SME is enabled in the second kernel Maybe it is unnecessary to support this case, because the old memory is unencrypted, the old memory can be dumped as usual, we don't need to enable sme in the second kernel, furthermore the requirement is rare in actual deployment. Another, If we must support the scenario, it will increase the complexity of the code, we will have to consider how to transfer the sme flag from the first kernel to the second kernel, in order to let the second kernel know that whether the old memory is encrypted. There are two manners to tranfer the SME flag to the second kernel, the first way is to modify the assembly code, which includes some common code and the path is too long. The second way is to use kexec tool, which could require the sme flag to be exported in the first kernel by "proc" or "sysfs", kexec will read the sme flag from "proc" or "sysfs" when we use kexec tool to load image, subsequently the sme flag will be saved in boot_params, we can properly remap the old memory according to the previously saved sme flag. Although we can fix this issue, maybe it is too expensive to do this. By the way, we won't fix the problem unless someone thinks it is necessary to do it. Test tools: makedumpfile[v1.6.3]: https://github.com/LianboJ/makedumpfile commit e1de103eca8f (A draft for kdump vmcore about AMD SME) Author: Lianbo Jiang <liji...@redhat.com> Date: Mon May 14 17:02:40 2018 +0800 Note: This patch can only dump vmcore in the case of SME enabled. crash-7.2.1: https://github.com/crash-utility/crash.git commit 1e1bd9c4c1be (Fix for the "bpf" command display on Linux 4.17-rc1) Author: Dave Anderson <ander...@redhat.com> Date: Fri May 11 15:54:32 2018 -0400 Test environment: HP ProLiant DL385Gen10 AMD EPYC 7251 8-Core Processor 32768 MB memory 600 GB disk space Linux 4.18-rc2: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git commit 7daf201d7fe8 ("Linux 4.18-rc2") Author: Linus Torvalds <torva...@linux-foundation.org> Date: Sun Jun 24 20:54:29 2018 +0800 Reference: AMD64 Architecture Programmer's Manual https://support.amd.com/TechDocs/24593.pdf Some changes: 1. remove the sme_active() check in __ioremap_caller(). 2. remove the '#ifdef' stuff throughout this patch. 3. put some logic into the early_memremap_pgprot_adjust() and clean the previous unnecessary changes, for example: arch/x86/include/asm/dmi.h, arch/x86/kernel/acpi/boot.c, drivers/acpi/tables.c. 4. add a new file and modify Makefile. 5. clean compile warning in copy_device_table() and some compile error. 6. split the original patch into five patches, it will be better for review. 7. modify elfcorehdr_read(). 8. add some comments. Some known issues: 1. about SME Upstream kernel doesn't work when we use kexec in the follow command. The system will hang on 'HP ProLiant DL385Gen10 AMD EPYC 7251'. But it can't reproduce on speedway. (This issue doesn't matter with the kdump patch.) Reproduce steps: # kexec -l /boot/vmlinuz-4.18.0-rc2+ --initrd=/boot/initramfs-4.18.0-rc2+.img --command-line="root=/dev/mapper/rhel_hp--dl385g10--03-root ro mem_encrypt=on rd.lvm.lv=rhel_hp-dl385g10-03/root rd.lvm.lv=rhel_hp-dl385g10-03/swap console=ttyS0,115200n81 LANG=en_US.UTF-8 earlyprintk=serial debug nokaslr" # kexec -e (or reboot) The system will hang: [ 1248.932239] kexec_core: Starting new kernel early console in extract_kernel input_data: 0x000000087e91c3b4 input_len: 0x000000000067fcbd output: 0x000000087d400000 output_len: 0x0000000001b6fa90 kernel_total_size: 0x0000000001a9d000 trampoline_32bit: 0x0000000000099000 Decompressing Linux... Parsing ELF... [-here the system will hang] 2. about SEV Upstream kernel(Host OS) doesn't work in host side, some drivers about SEV always go wrong in host side. We can't boot SEV Guest OS to test kdump patch. Maybe it is more reasonable to improve SEV in another patch. When some drivers can work in host side and it can also boot Virtual Machine(SEV Guest OS), it will be suitable to fix SEV for kdump. [ 369.426131] INFO: task systemd-udevd:865 blocked for more than 120 seconds. [ 369.433177] Not tainted 4.17.0-rc5+ #60 [ 369.437585] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [ 369.445783] systemd-udevd D 0 865 813 0x80000004 [ 369.451323] Call Trace: [ 369.453815] ? __schedule+0x290/0x870 [ 369.457523] schedule+0x32/0x80 [ 369.460714] __sev_do_cmd_locked+0x1f6/0x2a0 [ccp] [ 369.465556] ? cleanup_uevent_env+0x10/0x10 [ 369.470084] ? remove_wait_queue+0x60/0x60 [ 369.474219] ? 0xffffffffc0247000 [ 369.477572] __sev_platform_init_locked+0x2b/0x70 [ccp] [ 369.482843] sev_platform_init+0x1d/0x30 [ccp] [ 369.487333] psp_pci_init+0x40/0xe0 [ccp] [ 369.491380] ? 0xffffffffc0247000 [ 369.494936] sp_mod_init+0x18/0x1000 [ccp] [ 369.499071] do_one_initcall+0x4e/0x1d4 [ 369.502944] ? _cond_resched+0x15/0x30 [ 369.506728] ? kmem_cache_alloc_trace+0xae/0x1d0 [ 369.511386] ? do_init_module+0x22/0x220 [ 369.515345] do_init_module+0x5a/0x220 [ 369.519444] load_module+0x21cb/0x2a50 [ 369.523227] ? m_show+0x1c0/0x1c0 [ 369.526571] ? security_capable+0x3f/0x60 [ 369.530611] __do_sys_finit_module+0x94/0xe0 [ 369.534915] do_syscall_64+0x5b/0x180 [ 369.538607] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [ 369.543698] RIP: 0033:0x7f708e6311b9 [ 369.547536] RSP: 002b:00007ffff9d32aa8 EFLAGS: 00000246 ORIG_RAX: 0000000000000139 [ 369.555162] RAX: ffffffffffffffda RBX: 000055602a04c2d0 RCX: 00007f708e6311b9 [ 369.562346] RDX: 0000000000000000 RSI: 00007f708ef52039 RDI: 0000000000000008 [ 369.569801] RBP: 00007f708ef52039 R08: 0000000000000000 R09: 000055602a048b20 [ 369.576988] R10: 0000000000000008 R11: 0000000000000246 R12: 0000000000000000 [ 369.584177] R13: 000055602a075260 R14: 0000000000020000 R15: 0000000000000000 Lianbo Jiang (5): Add a function(ioremap_encrypted) for kdump when AMD sme enabled Allocate pages for kdump without encryption when SME is enabled Remap the device table of IOMMU in encrypted manner for kdump Adjust some permanent mappings in unencrypted ways for kdump when SME is enabled. Help to dump the old memory encrypted into vmcore file arch/x86/include/asm/io.h | 3 ++ arch/x86/kernel/Makefile | 1 + arch/x86/kernel/crash_dump_encrypt.c | 53 ++++++++++++++++++++++++++++++++++++ arch/x86/mm/ioremap.c | 36 ++++++++++++++++++------ drivers/iommu/amd_iommu_init.c | 14 ++++++++-- fs/proc/vmcore.c | 45 +++++++++++++++++++++++++----- include/linux/crash_dump.h | 12 ++++++++ kernel/kexec_core.c | 12 ++++++++ 8 files changed, 158 insertions(+), 18 deletions(-) create mode 100644 arch/x86/kernel/crash_dump_encrypt.c -- 2.9.5 _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
