Date:   Thu, 21 Jun 2018 09:21:16 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Lianbo Jiang <lijiang@...hat.com>
Cc:     linux-kernel@...r.kernel.org, thomas.lendacky@....com,
        iommu@...ts.linux-foundation.org, dyoung@...hat.com,
        kexec@...ts.infradead.org, akpm@...ux-foundation.org
Subject: Re: [PATCH 0/4 V3] Support kdump for AMD secure memory
 encryption(SME)

On 06/16/18 at 04:27pm, Lianbo Jiang wrote:
> It is convenient to remap the old memory encrypted to the second kernel by
> calling ioremap_encrypted().
> 
> 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        |

It's not clear to me here. If 1st kernel sme is off, in 2nd kernel, when
you remap the old memory with non-sme mode, why did it fail?

And please run scripts/get_maintainer.pl and add maintainers of
component which is affected in patch to CC list.

> |______________|_______________|_______________|
> 
> This patch is only for SME kdump, it is not support SEV kdump.
> 
> Test tools:
> makedumpfile[v1.6.3]: https://github.com/LianboJ/makedumpfile
> commit e1de103eca8f (A draft for kdump vmcore about AMD SME)
> Author: Lianbo Jiang <lijiang@...hat.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 <anderson@...hat.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 4.17-rc7:
> git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> commit b04e217704b7 ("Linux 4.17-rc7")
> Author: Linus Torvalds <torvalds@...ux-foundation.org>
> Date:   Sun May 27 13:01:47 2018 -0700
> 
> 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 four patches, it will be better for
> review.
> 
> Some known issues:
> 1. about SME
> Upstream kernel doesn't work when we use kexec in the follow command. The
> system will hang.
> (This issue doesn't matter with the kdump patch.)
> 
> Reproduce steps:
>  # kexec -l /boot/vmlinuz-4.17.0-rc7+ --initrd=/boot/initramfs-4.17.0-rc7+.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 (4):
>   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
>   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                | 28 +++++++++++++------
>  drivers/iommu/amd_iommu_init.c       | 15 +++++++++-
>  fs/proc/vmcore.c                     | 20 ++++++++++----
>  include/linux/crash_dump.h           | 11 ++++++++
>  kernel/kexec_core.c                  | 12 ++++++++
>  8 files changed, 128 insertions(+), 15 deletions(-)
>  create mode 100644 arch/x86/kernel/crash_dump_encrypt.c
> 
> -- 
> 2.9.5
> 
> 
> _______________________________________________
> kexec mailing list
> kexec@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/kexec

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