Re: [PATCH 0/4 v7] Support kdump for AMD secure memory encryption(SME)

[Lendacky, Thomas]

On 09/07/2018 03:18 AM, Lianbo Jiang wrote:
> When SME is enabled on AMD machine, we also need to support kdump. Because
> the memory is encrypted in the first kernel, we will remap the old memory
> to the kdump kernel for dumping data, and SME is also enabled in the kdump
> kernel, otherwise the old memory can not be decrypted.
> 
> 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 access the memory.
> 
> As we know, a page of memory that is marked as encrypted, which will be
> automatically decrypted when read from DRAM, and will also be automatically
> encrypted when written to DRAM. If the old memory is encrypted, we have to
> remap the old memory with the memory encryption mask, which will automatically
> decrypt the old memory when we read those data.
> 
> For kdump(SME), there are two cases that doesn't support:
> 
>  ----------------------------------------------
> | first-kernel | second-kernel | kdump support |
> |      (mem_encrypt=on|off)    |   (yes|no)    |
> |--------------+---------------+---------------|
> |     on       |     on        |     yes       |
> |     off      |     off       |     yes       |
> |     on       |     off       |     no        |
> |     off      |     on        |     no        |
> |______________|_______________|_______________|
> 
> 1. SME is enabled in the first kernel, but SME is disabled in kdump kernel
> In this case, because the old memory is encrypted, we can't decrypt the
> old memory.
> 
> 2. SME is disabled in the first kernel, but SME is enabled in kdump kernel
> It is unnecessary to support in this case, because the old memory is
> unencrypted, the old memory can be dumped as usual, we don't need to enable
> SME in kdump kernel. Another, If we must support the scenario, it will
> increase the complexity of the code, we will have to consider how to pass
> the SME flag from the first kernel to the kdump kernel, in order to let the
> kdump kernel know that whether the old memory is encrypted.
> 
> There are two methods to pass the SME flag to the kdump kernel. The first
> method is to modify the assembly code, which includes some common code and
> the path is too long. The second method is to use kexec tool, which could
> require the SME flag to be exported in the first kernel by "proc" or "sysfs",
> kexec tools will read the SME flag from "proc" or "sysfs" when we use kexec
> tools 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. But it is too expensive to do this.
> 
> This patches are only for SME kdump, the patches don't support SEV kdump.

Reviewed-by: Tom Lendacky <thomas.lendacky@xxxxxxx>

Just curious, are you planning to add SEV kdump support after this?

Also, a question below...

> 
> Test tools:
> makedumpfile[v1.6.3]: https://github.com/LianboJ/makedumpfile
> commit e1de103eca8f (A draft for kdump vmcore about AMD SME)
> Note: This patch can only dump vmcore in the case of SME enabled.
> 
> crash-7.2.3: https://github.com/crash-utility/crash.git
> commit 001f77a05585 (Fix for Linux 4.19-rc1 and later kernels that contain
>                      kernel commit7290d58095712a89f845e1bca05334796dd49ed2)
> 
> kexec-tools-2.0.17: git://git.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git
> commit b9de21ef51a7 (kexec: fix for "Unhandled rela relocation: R_X86_64_PLT32" error)
> Note:
> Before you load the kernel and initramfs for kdump, this patch(http://lists.infradead.org/pipermail/kexec/2018-September/021460.html)
> must be merged to kexec-tools, and then the kdump kernel will work well. Because there
> is a patch which is removed based on v6(x86/ioremap: strengthen the logic in early_memremap_pgprot_adjust()
> to adjust encryption mask).
> 
> Test environment:
> HP ProLiant DL385Gen10 AMD EPYC 7251
> 8-Core Processor
> 32768 MB memory
> 600 GB disk space
> 
> Linux 4.19-rc2:
> git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> commit 57361846b52bc686112da6ca5368d11210796804
> 
> Reference:
> AMD64 Architecture Programmer's Manual
> https://support.amd.com/TechDocs/24593.pdf
> 
> Changes since v6:
> 1. There is a patch which is removed based on v6.
> (x86/ioremap: strengthen the logic in early_memremap_pgprot_adjust() to adjust encryption mask)
> Dave Young suggests that this patch can be removed and fix the kexec-tools.
> Reference: http://lists.infradead.org/pipermail/kexec/2018-September/021460.html)
> 2. Update the patch log.
> 
> Some known issues:
> 1. about SME
> Upstream kernel will hang on HP machine(DL385Gen10 AMD EPYC 7251) when
> we execute the kexec command as follow:
> 
> # kexec -l /boot/vmlinuz-4.19.0-rc2+ --initrd=/boot/initramfs-4.19.0-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)
> 
> But this issue can not be reproduced on speedway machine, and this issue
> is irrelevant to my posted patches.
> 
> The kernel log:
> [ 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]

Do you know the reason for the hang?  It looks like it is hanging in
parse_elf().  Can you add some debug to parse_elf() to see if the
value of ehdr.e_phnum is valid (maybe it is not a valid value and so
the loop takes forever)?

Thanks,
Tom

> 
> 
> Lianbo Jiang (4):
>   x86/ioremap: add a function ioremap_encrypted() to remap kdump old
>     memory
>   kexec: allocate unencrypted control pages for kdump in case SME is
>     enabled
>   amd_iommu: remap the device table of IOMMU with the memory encryption
>     mask for kdump
>   kdump/vmcore: support encrypted old memory with SME enabled
> 
>  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                | 25 ++++++++-----
>  drivers/iommu/amd_iommu_init.c       | 14 ++++++--
>  fs/proc/vmcore.c                     | 21 +++++++----
>  include/linux/crash_dump.h           | 12 +++++++
>  kernel/kexec_core.c                  | 12 +++++++
>  8 files changed, 125 insertions(+), 16 deletions(-)
>  create mode 100644 arch/x86/kernel/crash_dump_encrypt.c
>