[PATCH v8 0/6] Support writable CPU ID registers from userspace

[Jing Zhang]

This patchset refactors/adds code to support writable per guest CPU ID feature
registers. Part of the code/ideas are from
https://lore.kernel.org/all/20220419065544.3616948-1-reijiw@google.com .
No functional change is intended in this patchset. With the new CPU ID feature
registers infrastructure, only writtings of ID_AA64PFR0_EL1.[CSV2|CSV3],
ID_AA64DFR0_EL1.PMUVer and ID_DFR0_ELF.PerfMon are allowed as KVM does before.

Writable (Configurable) per guest CPU ID feature registers are useful for
creating/migrating guest on ARM CPUs with different kinds of features.

This patchset uses kvm->arch.config_lock from Oliver's lock inversion fixes at
https://lore.kernel.org/linux-arm-kernel/20230327164747.2466958-1-oliver.upton@linux.dev/

---

* v7 -> v8
  - Move idregs table sanity check to kvm_sys_reg_table_init.
  - Only allow userspace writing before VM running.
  - No lock is hold for guest access to idregs.
  - Addressed some other comments from Reiji and Oliver.

* v6 -> v7
  - Rebased to v6.3-rc7.
  - Add helpers for idregs read/write.
  - Guard all idregs reads/writes.
  - Add code to fix features' safe value type which is different for KVM than
    for the host.

* v5 -> v6
  - Rebased to v6.3-rc5.
  - Reuse struct sys_reg_desc's reset() callback and field val for KVM.
    sanitisation function and writable mask instead of creating a new data
    structure for idregs.
  - Use get_arm64_ftr_reg() instead of exposing idregs ftr_bits array.

* v4 -> v5
  - Rebased to 2fad20ae05cb (kvmarm/next)
    Merge branch kvm-arm64/selftest/misc-6,4 into kvmarm-master/next
  - Use kvm->arch.config_lock to guard update to multiple VM scope idregs
    to avoid lock inversion
  - Add back IDREG() macro for idregs access
  - Refactor struct id_reg_desc by using existing infrastructure.
  - Addressed many other comments from Marc.

* v3 -> v4
  - Remove IDREG() macro for ID reg access, use simple array access instead
  - Rename kvm_arm_read_id_reg_with_encoding() to kvm_arm_read_id_reg()
  - Save perfmon value in ID_DFR0_EL1 instead of pmuver
  - Update perfmon in ID_DFR0_EL1 and pmuver in ID_AA64DFR0_EL1 atomically
  - Remove kvm_vcpu_has_pmu() in macro kvm_pmu_is_3p5()
  - Improve ID register sanity checking in kvm_arm_check_idreg_table()

* v2 -> v3
  - Rebased to 96a4627dbbd4 (kvmarm/next)
    Merge tag ' https://github.com/oupton/linux tags/kvmarm-6.3' from into kvmarm-master/next
  - Add id registere emulation entry point function emulate_id_reg
  - Fix consistency for ID_AA64DFR0_EL1.PMUVer and ID_DFR0_EL1.PerfMon
  - Improve the checking for id register table by ensuring that every entry has
    the correct id register encoding.
  - Addressed other comments from Reiji and Marc.

* v1 -> v2
  - Rebase to 7121a2e1d107 (kvmarm/next) Merge branch kvm-arm64/nv-prefix into kvmarm/next
  - Address writing issue for PMUVer

[1] https://lore.kernel.org/all/20230201025048.205820-1-jingzhangos@google.com
[2] https://lore.kernel.org/all/20230212215830.2975485-1-jingzhangos@google.com
[3] https://lore.kernel.org/all/20230228062246.1222387-1-jingzhangos@google.com
[4] https://lore.kernel.org/all/20230317050637.766317-1-jingzhangos@google.com
[5] https://lore.kernel.org/all/20230402183735.3011540-1-jingzhangos@google.com
[6] https://lore.kernel.org/all/20230404035344.4043856-1-jingzhangos@google.com
[7] https://lore.kernel.org/all/20230424234704.2571444-1-jingzhangos@google.com

---

Jing Zhang (6):
  KVM: arm64: Move CPU ID feature registers emulation into a separate
    file
  KVM: arm64: Save ID registers' sanitized value per guest
  KVM: arm64: Use per guest ID register for ID_AA64PFR0_EL1.[CSV2|CSV3]
  KVM: arm64: Use per guest ID register for ID_AA64DFR0_EL1.PMUVer
  KVM: arm64: Reuse fields of sys_reg_desc for idreg
  KVM: arm64: Refactor writings for PMUVer/CSV2/CSV3

 arch/arm64/include/asm/cpufeature.h |   1 +
 arch/arm64/include/asm/kvm_host.h   |  33 +-
 arch/arm64/kernel/cpufeature.c      |   2 +-
 arch/arm64/kvm/Makefile             |   2 +-
 arch/arm64/kvm/arm.c                |  24 +-
 arch/arm64/kvm/id_regs.c            | 717 ++++++++++++++++++++++++++++
 arch/arm64/kvm/sys_regs.c           | 534 ++++-----------------
 arch/arm64/kvm/sys_regs.h           |  28 +-
 include/kvm/arm_pmu.h               |   5 +-
 9 files changed, 864 insertions(+), 482 deletions(-)
 create mode 100644 arch/arm64/kvm/id_regs.c


base-commit: 6a8f57ae2eb07ab39a6f0ccad60c760743051026
-- 
2.40.1.495.gc816e09b53d-goog