system/arm/cpu-features.rst

5 choose to implement or not.  In QEMU, optional CPU features have
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.
23 QEMU's support may be limited for some CPU features, only partially
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 -------------------------------------
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``
156 QEMU command line with that CPU type::
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
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``
217   When ``pauth`` is enabled, select the QEMU implementation defined algorithm.
219 ``pauth-qarma3``
222 ``pauth-qarma5``
225 Without ``pauth-impdef``, ``pauth-qarma3`` or ``pauth-qarma5`` enabled,
226 the QEMU impdef algorithm is used.  The architected QARMA5
228 be quite slow to emulate.  The impdef algorithm used by QEMU is
229 non-cryptographic but significantly faster.
247 ---------------------------------------------
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 ----------------------------------
270      the guest.  However QEMU will still track any ``sve<N>`` CPU
278      KVM is not in use means including the non-power-of-two lengths, and,
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.
312      Dependencies and Constraints", which will even be auto-enabled if
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
411 length supported by QEMU is 256.
413 If this property is set to ``-1`` then the default vector length
430 length supported by qemu is 2048 bits.  Otherwise, there are no
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-``
455 The method for enabling RME will change in some future QEMU release
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
468 removed in some future QEMU release.