system/arm/cpu-features.rst

10 Cortex-A15 and the Cortex-A57, which respectively implement Arm
11 architecture reference manuals ARMv7-A and ARMv8-A, may both optionally
12 implement PMUs.  For example, if a user wants to use a Cortex-A15 without
13 a PMU, then the ``-cpu`` parameter should contain ``pmu=off`` on the QEMU
14 command line, i.e. ``-cpu cortex-a15,pmu=off``.
18 that implement the ARMv8-A architecture reference manual may optionally
20 ``aarch64`` CPU property.  A CPU type such as the Cortex-A15, which does
21 not implement ARMv8-A, will not have the ``aarch64`` CPU property.
30 prefixed with "kvm-" and are described in "KVM VCPU Features".
36 CPU type is possible with the ``query-cpu-model-expansion`` QMP command.
37 Below are some examples where ``scripts/qmp/qmp-shell`` (see the top comment
41    (Note, we started QEMU with qemu-system-aarch64, so ``max`` is
42    implementing the ARMv8-A reference manual in this case)::
44       (QEMU) query-cpu-model-expansion type=full model={"name":"max"}
64       (QEMU) query-cpu-model-expansion type=full model={"name":"max","props":{"pmu":false}}
78       (QEMU) query-cpu-model-expansion type=full model={"name":"max","props":{"aarch64":false}}
81        "'aarch64' feature cannot be disabled unless KVM is enabled and 32-bit EL1 is supported"
90       (QEMU) query-cpu-model-expansion type=full model={"name":"max","props":{"sve":false}}
102 (5) Let's try probing CPU features for the Cortex-A15 CPU type::
104       (QEMU) query-cpu-model-expansion type=full model={"name":"cortex-a15"}
105       {"return": {"model": {"name": "cortex-a15", "props": {"pmu": true}}}}
110 -------------------------------------
113 it may be possible to change one feature at a time without error, but
123 -------------------------------
126 that do work, e.g. using the named CPU model ``cortex-a57`` with KVM on a
135 Enabling KVM also affects the ``query-cpu-model-expansion`` QMP command.  The
142 above, the ``cortex-a57`` CPU type is also valid when KVM is enabled.
144 then attempt to query ``cortex-a57``, however that query will fail with our
147 some time.  Additionally, if the KVM-enabled QEMU instance running on a
148 seattle host is using the ``cortex-a57`` CPU type, then querying ``cortex-a57``
158   $ qemu-system-aarch64 -M virt -cpu max,pmu=off,sve=on,sve128=on,sve256=on
176 are named with the prefix "kvm-".  KVM VCPU features may be probed,
180 ``kvm-no-adjvtime``
181   By default kvm-no-adjvtime is disabled.  This means that by default
182   the virtual time adjustment is enabled (vtime is not *not* adjusted).
184   When virtual time adjustment is enabled each time the VM transitions
186   ensure stopped time is not counted.  This avoids time jumps
191   that does not subtract VM stopped time.  The guest may resynchronize
192   its virtual counter with other time sources as needed.
194   Enable kvm-no-adjvtime to disable virtual time adjustment, also
195   restoring the legacy (pre-5.0) behavior.
197 ``kvm-steal-time``
198   Since v5.2, kvm-steal-time is enabled by default when KVM is
199   enabled, the feature is supported, and the guest is 64-bit.
201   When kvm-steal-time is enabled a 64-bit guest can account for time
216 ``pauth-impdef``
219 ``pauth-qarma3``
222 ``pauth-qarma5``
225 Without ``pauth-impdef``, ``pauth-qarma3`` or ``pauth-qarma5`` enabled,
229 non-cryptographic but significantly faster.
247 ---------------------------------------------
249   1) At least one vector length must be enabled when ``sve`` is enabled.
253      KVM is not enabled, then only all the smaller, power-of-two vector
255      vector lengths up to 512-bits (128, 256, 384, 512), then if ``sve512``
256      is enabled, the 128-bit vector length, 256-bit vector length, and
257      384-bit vector length must also be enabled. Without KVM, the 384-bit
265 ----------------------------------
278      KVM is not in use means including the non-power-of-two lengths, and,
286   4) If one or more vector lengths have been explicitly enabled and at
287      least one of the dependency lengths of the maximum enabled length
300   7) If one or more ``sve<N>`` CPU properties are set ``off``, but no ``sve<N>``,
303      When KVM is not enabled, disabling a power-of-two vector length also
304      disables all vector lengths larger than the power-of-two length.
309   8) If one or more ``sve<N>`` CPU properties are set to ``on``, then they
312      Dependencies and Constraints", which will even be auto-enabled if
318      provided an error will be generated.  To avoid this error, one must
319      enable at least one vector length prior to enabling SVE.
322 -------------------------
326      $ qemu-system-aarch64 -M virt -cpu max,sve=off
330      $ qemu-system-aarch64 -M virt -cpu max
335      $ qemu-system-aarch64 -M virt,accel=kvm -cpu host
337   4) Only enable the 128-bit vector length::
339      $ qemu-system-aarch64 -M virt -cpu max,sve128=on
341   5) Disable the 512-bit vector length and all larger vector lengths,
342      since 512 is a power-of-two.  This results in all the smaller,
345      $ qemu-system-aarch64 -M virt -cpu max,sve512=off
347   6) Enable the 128-bit, 256-bit, and 512-bit vector lengths::
349      $ qemu-system-aarch64 -M virt -cpu max,sve128=on,sve256=on,sve512=on
351   7) The same as (6), but since the 128-bit and 256-bit vector
352      lengths are required for the 512-bit vector length to be enabled,
353      then allow them to be auto-enabled::
355      $ qemu-system-aarch64 -M virt -cpu max,sve512=on
357   8) Do the same as (7), but by first disabling SVE and then re-enabling it::
359      $ qemu-system-aarch64 -M virt -cpu max,sve=off,sve512=on,sve=on
363      $ qemu-system-aarch64 -M virt -cpu max,sve128=off
364      $ qemu-system-aarch64 -M virt -cpu max,sve=off,sve128=off,sve=on
367 --------------------------------
376 -------------------------
380      $ qemu-system-aarch64 -M virt -cpu max,sme=off
384      $ qemu-system-aarch64 -M virt -cpu max
386   3) Only enable the 256-bit vector length::
388      $ qemu-system-aarch64 -M virt -cpu max,sme256=on
390   3) Enable the 256-bit and 1024-bit vector lengths::
392      $ qemu-system-aarch64 -M virt -cpu max,sme256=on,sme1024=on
394   4) Disable the 512-bit vector length.  This results in all the other
398      $ qemu-system-aarch64 -M virt -cpu max,sve512=off
400 SVE User-mode Default Vector Length Property
401 --------------------------------------------
403 For qemu-aarch64, the cpu property ``sve-default-vector-length=N`` is
413 If this property is set to ``-1`` then the default vector length
426 SME is not supported by KVM at this time.
428 At least one vector length must be enabled when ``sme`` is enabled,
433 SME User-mode Default Vector Length Property
434 --------------------------------------------
436 For qemu-aarch64, the cpu property ``sme-default-vector-length=N`` is
442 As with ``sve-default-vector-length``, if the default length is larger
444 be reduced.  If this property is set to ``-1`` then the default vector
450 The status of RME support with QEMU is experimental.  At this time we
452 The feature is enabled by the CPU property ``x-rme``, with the ``x-``
459 -----------------------------
462 configurations, ``x-l0gptsz=S`` may be used to specify the value
463 to encode into ``GPCCR_EL3.L0GPTSZ``, a read-only field that
467 As with ``x-rme``, the ``x-l0gptsz`` property may be renamed or