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Ashish Kalra 88a921aa3c x86/sev: Ensure that RMP table fixups are reserved 
The BIOS reserves RMP table memory via e820 reservations. This can still lead
to RMP page faults during kexec if the host tries to access memory within the
same 2MB region.

Commit

  400fea4b96 ("x86/sev: Add callback to apply RMP table fixups for kexec"

adjusts the e820 reservations for the RMP table so that the entire 2MB range
at the start/end of the RMP table is marked reserved.

The e820 reservations are then passed to firmware via SNP_INIT where they get
marked HV-Fixed.

The RMP table fixups are done after the e820 ranges have been added to
memblock, allowing the fixup ranges to still be allocated and used by the
system.

The problem is that this memory range is now marked reserved in the e820
tables and during SNP initialization these reserved ranges are marked as
HV-Fixed.  This means that the pages cannot be used by an SNP guest, only by
the hypervisor.

However, the memory management subsystem does not make this distinction and
can allocate one of those pages to an SNP guest. This will ultimately result
in RMPUPDATE failures associated with the guest, causing it to fail to start
or terminate when accessing the HV-Fixed page.

The issue is captured below with memblock=debug:

  [    0.000000] SEV-SNP: *** DEBUG: snp_probe_rmptable_info:352 - rmp_base=0x280d4800000, rmp_end=0x28357efffff
  ...
  [    0.000000] BIOS-provided physical RAM map:
  ...
  [    0.000000] BIOS-e820: [mem 0x00000280d4800000-0x0000028357efffff] reserved
  [    0.000000] BIOS-e820: [mem 0x0000028357f00000-0x0000028357ffffff] usable
  ...
  ...
  [    0.183593] memblock add: [0x0000028357f00000-0x0000028357ffffff] e820__memblock_setup+0x74/0xb0
  ...
  [    0.203179] MEMBLOCK configuration:
  [    0.207057]  memory size = 0x0000027d0d194000 reserved size = 0x0000000009ed2c00
  [    0.215299]  memory.cnt  = 0xb
  ...
  [    0.311192]  memory[0x9]     [0x0000028357f00000-0x0000028357ffffff], 0x0000000000100000 bytes flags: 0x0
  ...
  ...
  [    0.419110] SEV-SNP: Reserving start/end of RMP table on a 2MB boundary [0x0000028357e00000]
  [    0.428514] e820: update [mem 0x28357e00000-0x28357ffffff] usable ==> reserved
  [    0.428517] e820: update [mem 0x28357e00000-0x28357ffffff] usable ==> reserved
  [    0.428520] e820: update [mem 0x28357e00000-0x28357ffffff] usable ==> reserved
  ...
  ...
  [    5.604051] MEMBLOCK configuration:
  [    5.607922]  memory size = 0x0000027d0d194000 reserved size = 0x0000000011faae02
  [    5.616163]  memory.cnt  = 0xe
  ...
  [    5.754525]  memory[0xc]     [0x0000028357f00000-0x0000028357ffffff], 0x0000000000100000 bytes on node 0 flags: 0x0
  ...
  ...
  [   10.080295] Early memory node ranges[   10.168065]
  ...
  node   0: [mem 0x0000028357f00000-0x0000028357ffffff]
  ...
  ...
  [ 8149.348948] SEV-SNP: RMPUPDATE failed for PFN 28357f7c, pg_level: 1, ret: 2

As shown above, the memblock allocations show 1MB after the end of the RMP as
available for allocation, which is what the RMP table fixups have reserved.
This memory range subsequently gets allocated as SNP guest memory, resulting
in an RMPUPDATE failure.

This can potentially be fixed by not reserving the memory range in the e820
table, but that causes kexec failures when using the KEXEC_FILE_LOAD syscall.

The solution is to use memblock_reserve() to mark the memory reserved for the
system, ensuring that it cannot be allocated to an SNP guest.

Since HV-Fixed memory is still readable/writable by the host, this only ends
up being a problem if the memory in this range requires a page state change,
which generally will only happen when allocating memory in this range to be
used for running SNP guests, which is now possible with the SNP hypervisor
support in kernel 6.11.

Backporter note:

Fixes tag points to a 6.9 change but as the last paragraph above explains,
this whole thing can happen after 6.11 received SNP HV support, therefore
backporting to 6.9 is not really necessary.

  [ bp: Massage commit message. ]

Fixes: 400fea4b96 ("x86/sev: Add callback to apply RMP table fixups for kexec")
Suggested-by: Thomas Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Cc: <stable@kernel.org> # 6.11, see Backporter note above.
Link: https://lore.kernel.org/r/20240815221630.131133-1-Ashish.Kalra@amd.com
2024-10-23 12:34:06 +02:00
arch x86/sev: Ensure that RMP table fixups are reserved 2024-10-23 12:34:06 +02:00
block block-6.12-20241004 2024-10-04 10:43:44 -07:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto move asm/unaligned.h to linux/unaligned.h 2024-10-02 17:23:23 -04:00
Documentation platform-drivers-x86 for v6.12-2 2024-10-06 11:11:01 -07:00
drivers platform-drivers-x86 for v6.12-2 2024-10-06 11:11:01 -07:00
fs bcachefs fixes for 6.12-rc2 2024-10-05 15:18:04 -07:00
include Power management fixes for 6.12-rc2 2024-10-04 11:57:15 -07:00
init cfi: encode cfi normalized integers + kasan/gcov bug in Kconfig 2024-09-26 21:27:27 +02:00
io_uring io_uring/net: harden multishot termination case for recv 2024-09-30 08:26:59 -06:00
ipc struct fd layout change (and conversion to accessor helpers) 2024-09-23 09:35:36 -07:00
kernel Various fixes for tracing: 2024-10-04 12:11:06 -07:00
lib slab fixes for 6.12-rc1 2024-10-04 12:05:39 -07:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm mm, slab: suppress warnings in test_leak_destroy kunit test 2024-10-02 16:28:46 +02:00
net Including fixes from ieee802154, bluetooth and netfilter. 2024-10-03 09:44:00 -07:00
rust rust: kunit: use C-string literals to clean warning 2024-10-01 23:46:42 +02:00
samples [tree-wide] finally take no_llseek out 2024-09-27 08:18:43 -07:00
scripts kbuild: deb-pkg: Remove blank first line from maint scripts 2024-10-07 02:36:38 +09:00
security hardening fixes for v6.12-rc2 2024-10-05 10:19:14 -07:00
sound sound fixes for 6.12-rc2 2024-10-04 11:29:46 -07:00
tools ARM64: 2024-10-06 10:53:28 -07:00
usr initramfs: shorten cmd_initfs in usr/Makefile 2024-07-16 01:07:52 +09:00
virt x86: 2024-09-28 09:20:14 -07:00
.clang-format clang-format: Update with v6.11-rc1's for_each macro list 2024-08-02 13:20:31 +02:00
.cocciconfig
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore Add Jeff Kirsher to .get_maintainer.ignore 2024-03-08 11:36:54 +00:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore Kbuild updates for v6.12 2024-09-24 13:02:06 -07:00
.mailmap Summary 2024-09-24 11:08:40 -07:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Mark powerpc spufs as orphaned 2024-08-19 21:27:56 +10:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS platform-drivers-x86 for v6.12-2 2024-10-06 11:11:01 -07:00
Makefile Linux 6.12-rc2 2024-10-06 15:32:27 -07:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.