mirror of
https://github.com/xen-project/xen.git
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Andrew Cooper
6f1b280876
This is long overdue, and we need to start somewhere. Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> Acked-by: Jan Beulich <jbeulich@suse.com>
72 lines
2.6 KiB
ReStructuredText
72 lines
2.6 KiB
ReStructuredText
.. SPDX-License-Identifier: CC-BY-4.0
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Frequently Asked Questions
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==========================
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How do I...
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-----------
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... check whether a Kconfig option is active?
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Kconfig is a build time configuration system, combining inherent knowledge,
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the capabilities of the toolchain, and explicit user choice to form a
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configuration of a build of Xen.
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A file, by default ``.config``, is produced by the build identifying the
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configuration used. Kconfig symbols all start with ``CONFIG_``, and come in
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a variety of types including strings, integers and booleans. Booleans are
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the most common, and when active are expressed with ``...=y``. e.g.::
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xen.git/xen$ grep CONFIG_FOO .config
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CONFIG_FOO_BOOLEAN=y
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CONFIG_FOO_STRING="lorem ipsum"
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CONFIG_FOO_INTEGER=42
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Symbols which are either absent, or expressed as ``... is not set`` are
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disabled. e.g.::
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xen.git/xen$ grep CONFIG_BAR .config
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# CONFIG_BAR is not set
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Builds of Xen configured with ``CONFIG_HYPFS_CONFIG=y`` embed their own
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``.config`` at build time, and can provide it to the :term:`control domain`
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upon requested. e.g.::
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[root@host ~]# xenhypfs cat /buildinfo/config | grep -e FOO -e BAR
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CONFIG_FOO=y
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# CONFIG_BAR is not set
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... tell if CET is active?
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^^^^^^^^^^^^^^^^^^^^^^^^^^
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Control-flow Enforcement Technology support was added to Xen 4.14. It is
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build time conditional, dependent on both having a new-enough toolchain and
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an explicit Kconfig option, and also requires capable hardware. See
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:term:`CET`.
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For CET-SS, Shadow Stacks, the minimum toolchain requirements are ``binutils
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>= 2.29`` or ``LLVM >= 6``. No specific compiler support is required.
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Check for ``CONFIG_XEN_SHSTK`` being active.
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For CET-IBT, Indirect Branch Tracking, the minimum toolchain requirements
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are ``GCC >= 9`` and ``binutils >= 2.29``. Xen relies on a compiler feature
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which is specific to GCC at the time of writing. Check for
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``CONFIG_XEN_IBT`` being active.
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If a capable Xen is booted on capable hardware, and CET is not disabled by
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command line option or errata, Xen will print some details early on boot
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about which CET facilities have been turned on::
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...
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(XEN) CPU Vendor: Intel, Family 6 (0x6), Model 143 (0x8f), Stepping 8 (raw 000806f8)
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(XEN) Enabling Supervisor Shadow Stacks
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(XEN) Enabling Indirect Branch Tracking
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(XEN) - IBT disabled in UEFI Runtime Services
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(XEN) EFI RAM map:
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...
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This can be obtained from the control domain with ``xl dmesg``, but remember
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to confirm that the console ring hasn't wrapped.
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