[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [PATCH v7 03/12] docs: add feature document for Xen hypervisor sysfs-like support
On the 2019 Xen developer summit there was agreement that the Xen hypervisor should gain support for a hierarchical name-value store similar to the Linux kernel's sysfs. In the beginning there should only be basic support: entries can be added from the hypervisor itself only, there is a simple hypercall interface to read the data. Add a feature document for setting the base of a discussion regarding the desired functionality and the entries to add. Signed-off-by: Juergen Gross <jgross@xxxxxxxx> Acked-by: Julien Grall <jgrall@xxxxxxxxxx> --- V1: - remove the "--" prefixes of the sub-commands of the user tool (Jan Beulich) - rename xenfs to xenhypfs (Jan Beulich) - add "tree" and "write" options to user tool V2: - move example tree to the paths description (Ian Jackson) - specify allowed characters for keys and values (Ian Jackson) V3: - correct introduction (writable entries) V4: - add list specification - add entry example (Julien Grall) - correct date and Xen version (Julien Grall) - add ARM64 as possible architecture (Julien Grall) - add version description to the feature doc (Jan Beulich) --- docs/features/hypervisorfs.pandoc | 92 +++++++++++++++++++++++++++++++++ docs/misc/hypfs-paths.pandoc | 105 ++++++++++++++++++++++++++++++++++++++ 2 files changed, 197 insertions(+) create mode 100644 docs/features/hypervisorfs.pandoc create mode 100644 docs/misc/hypfs-paths.pandoc diff --git a/docs/features/hypervisorfs.pandoc b/docs/features/hypervisorfs.pandoc new file mode 100644 index 0000000000..a0a0ead057 --- /dev/null +++ b/docs/features/hypervisorfs.pandoc @@ -0,0 +1,92 @@ +% Hypervisor FS +% Revision 1 + +\clearpage + +# Basics +---------------- --------------------- + Status: **Supported** + + Architectures: all + + Components: Hypervisor, toolstack +---------------- --------------------- + +# Overview + +The Hypervisor FS is a hierarchical name-value store for reporting +information to guests, especially dom0. It is similar to the Linux +kernel's sysfs. Entries and directories are created by the hypervisor, +while the toolstack is able to use a hypercall to query the entry +values or (if allowed by the hypervisor) to modify them. + +# User details + +With: + + xenhypfs ls <path> + +the user can list the entries of a specific path of the FS. Using: + + xenhypfs cat <path> + +the content of an entry can be retrieved. Using: + + xenhypfs write <path> <string> + +a writable entry can be modified. With: + + xenhypfs tree + +the complete Hypervisor FS entry tree can be printed. + +The FS paths are documented in `docs/misc/hypfs-paths.pandoc`. + +# Technical details + +Access to the hypervisor filesystem is done via the stable new hypercall +__HYPERVISOR_filesystem_op. This hypercall supports a sub-command +XEN_HYPFS_OP_get_version which will return the highest version of the +interface supported by the hypervisor. Additions to the interface need +to bump the interface version. The hypervisor is required to support the +previous interface versions, too (this implies that additions will always +require new sub-commands in order to allow the hypervisor to decide which +version of the interface to use). + +* hypercall interface specification + * `xen/include/public/hypfs.h` +* hypervisor internal files + * `xen/include/xen/hypfs.h` + * `xen/common/hypfs.c` +* `libxenhypfs` + * `tools/libs/libxenhypfs/*` +* `xenhypfs` + * `tools/misc/xenhypfs.c` +* path documentation + * `docs/misc/hypfs-paths.pandoc` + +# Testing + +Any new parameters or hardware mitigations should be verified to show up +correctly in the filesystem. + +# Areas for improvement + +* More detailed access rights +* Entries per domain and/or per cpupool + +# Known issues + +* None + +# References + +* None + +# History + +------------------------------------------------------------------------ +Date Revision Version Notes +---------- -------- -------- ------------------------------------------- +2020-01-23 1 Xen 4.14 Document written +---------- -------- -------- ------------------------------------------- diff --git a/docs/misc/hypfs-paths.pandoc b/docs/misc/hypfs-paths.pandoc new file mode 100644 index 0000000000..b9f50f6998 --- /dev/null +++ b/docs/misc/hypfs-paths.pandoc @@ -0,0 +1,105 @@ +# Xenhypfs Paths + +This document attempts to define all the paths which are available +in the Xen hypervisor file system (hypfs). + +The hypervisor file system can be accessed via the xenhypfs tool. + +## Notation + +The hypervisor file system is similar to the Linux kernel's sysfs. +In this document directories are always specified with a trailing "/". + +The following notation conventions apply: + + DIRECTORY/ + + PATH = VALUES [TAGS] + +The first syntax defines a directory. It normally contains related +entries and the general scope of the directory is described. + +The second syntax defines a file entry containing values which are +either set by the hypervisor or, if the file is writable, can be set +by the user. + +PATH can contain simple regex constructs following the Perl compatible +regexp syntax described in pcre(3) or perlre(1). + +A hypervisor file system entry name can be any 0-delimited byte string +not containing any '/' character. The names "." and ".." are reserved +for file system internal use. + +VALUES are strings and can take the following forms: + +* STRING -- an arbitrary 0-delimited byte string. +* INTEGER -- An integer, in decimal representation unless otherwise + noted. +* "a literal string" -- literal strings are contained within quotes. +* (VALUE | VALUE | ... ) -- a set of alternatives. Alternatives are + separated by a "|" and all the alternatives are enclosed in "(" and + ")". +* {VALUE, VALUE, ... } -- a list of possible values separated by "," and + enclosed in "{" and "}". + +Additional TAGS may follow as a comma separated set of the following +tags enclosed in square brackets. + +* w -- Path is writable by the user. This capability is usually + limited to the control domain (e.g. dom0). +* ARM | ARM32 | ARM64 | X86: the path is available for the respective + architecture only. +* PV -- Path is valid for PV capable hypervisors only. +* HVM -- Path is valid for HVM capable hypervisors only. +* CONFIG_* -- Path is valid only in case the hypervisor was built with + the respective config option. + +So an entry could look like this: + + /cpu-bugs/active-pv/xpti = ("No"|{"dom0", "domU", "PCID on"}) [w,X86,PV] + +Possible values would be "No" or a list of "dom0", "domU", and "PCID on". +The entry would be writable and it would exist on X86 only and only if the +hypervisor is configured to support PV guests. + +## Example + +A populated Xen hypervisor file system might look like the following example: + + / + buildinfo/ directory containing build-time data + config contents of .config file used to build Xen + cpu-bugs/ x86: directory of cpu bug information + l1tf "Vulnerable" or "Not vulnerable" + mds "Vulnerable" or "Not vulnerable" + meltdown "Vulnerable" or "Not vulnerable" + spec-store-bypass "Vulnerable" or "Not vulnerable" + spectre-v1 "Vulnerable" or "Not vulnerable" + spectre-v2 "Vulnerable" or "Not vulnerable" + mitigations/ directory of mitigation settings + bti-thunk "N/A", "RETPOLINE", "LFENCE" or "JMP" + spec-ctrl "No", "IBRS+" or IBRS-" + ibpb "No" or "Yes" + l1d-flush "No" or "Yes" + md-clear "No" or "VERW" + l1tf-barrier "No" or "Yes" + active-hvm/ directory for mitigations active in hvm doamins + msr-spec-ctrl "No" or "Yes" + rsb "No" or "Yes" + eager-fpu "No" or "Yes" + md-clear "No" or "Yes" + active-pv/ directory for mitigations active in pv doamins + msr-spec-ctrl "No" or "Yes" + rsb "No" or "Yes" + eager-fpu "No" or "Yes" + md-clear "No" or "Yes" + xpti "No" or list of "dom0", "domU", "PCID on" + l1tf-shadow "No" or list of "dom0", "domU" + params/ directory with hypervisor parameter values + (boot/runtime parameters) + +## General Paths + +#### / + +The root of the hypervisor file system. -- 2.16.4
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