[v5,0/5] KVM: arm64: PMU: Fix SET_ONE_REG for vPMC regs

Message

Akihiko Odaki March 15, 2025, 9:12 a.m. UTC

Prepare vPMC registers for user-initiated changes after first run. This
is important specifically for debugging Windows on QEMU with GDB; QEMU
tries to write back all visible registers when resuming the VM execution
with GDB, corrupting the PMU state. Windows always uses the PMU so this
can cause adverse effects on that particular OS.

This series also contains patch "KVM: arm64: PMU: Set raw values from
user to PM{C,I}NTEN{SET,CLR}, PMOVS{SET,CLR}", which reverts semantic
changes made for the mentioned registers in the past. It is necessary
to migrate the PMU state properly on Firecracker, QEMU, and crosvm.

Signed-off-by: Akihiko Odaki <[e-mail]>
---
Changes in v5:
- Rebased.
- Link to v4: https://lore.kernel.org/r/[e-mail]

Changes in v4:
- Reverted changes for functions implementing ioctls in patch
  "KVM: arm64: PMU: Assume PMU presence in pmu-emul.c".
- Removed kvm_pmu_vcpu_reset().
- Reordered function calls in kvm_vcpu_reload_pmu() for better style.
- Link to v3: https://lore.kernel.org/r/[e-mail]

Changes in v3:
- Added patch "KVM: arm64: PMU: Assume PMU presence in pmu-emul.c".
- Added an explanation of this path series' motivation to each patch.
- Explained why userspace register writes and register reset should be
  covered in patch "KVM: arm64: PMU: Reload when user modifies
  registers".
- Marked patch "KVM: arm64: PMU: Set raw values from user to
  PM{C,I}NTEN{SET,CLR}, PMOVS{SET,CLR}" for stable.
- Reoreded so that patch "KVM: arm64: PMU: Set raw values from user to
  PM{C,I}NTEN{SET,CLR}, PMOVS{SET,CLR}" would come first.
- Added patch "KVM: arm64: PMU: Call kvm_pmu_handle_pmcr() after masking
  PMCNTENSET_EL0".
- Added patch "KVM: arm64: Reload PMCNTENSET_EL0".
- Link to v2: https://lore.kernel.org/r/[e-mail]

Changes in v2:
- Changed to utilize KVM_REQ_RELOAD_PMU as suggested by Oliver Upton.
- Added patch "KVM: arm64: PMU: Reload when user modifies registers"
  to cover more registers.
- Added patch "KVM: arm64: PMU: Set raw values from user to
  PM{C,I}NTEN{SET,CLR}, PMOVS{SET,CLR}".
- Link to v1: https://lore.kernel.org/r/[e-mail]

---
Akihiko Odaki (5):
      KVM: arm64: PMU: Set raw values from user to PM{C,I}NTEN{SET,CLR}, PMOVS{SET,CLR}
      KVM: arm64: PMU: Assume PMU presence in pmu-emul.c
      KVM: arm64: PMU: Fix SET_ONE_REG for vPMC regs
      KVM: arm64: PMU: Reload when user modifies registers
      KVM: arm64: PMU: Reload when resetting

 arch/arm64/kvm/arm.c            | 17 ++++++++-----
 arch/arm64/kvm/emulate-nested.c |  6 +++--
 arch/arm64/kvm/pmu-emul.c       | 56 +++++++++++------------------------------
 arch/arm64/kvm/reset.c          |  3 ---
 arch/arm64/kvm/sys_regs.c       | 52 ++++++++++++++++++++++----------------
 include/kvm/arm_pmu.h           |  4 +--
 6 files changed, 62 insertions(+), 76 deletions(-)
---
base-commit: 80e54e84911a923c40d7bee33a34c1b4be148d7a
change-id: 20250302-pmc-b90a86af945c

Best regards,

Comments

Marc Zyngier March 16, 2025, 10:33 a.m. UTC | #1

On Sat, 15 Mar 2025 09:12:09 +0000,
Akihiko Odaki <[e-mail]> wrote:
> 
> Prepare vPMC registers for user-initiated changes after first run. This
> is important specifically for debugging Windows on QEMU with GDB; QEMU
> tries to write back all visible registers when resuming the VM execution
> with GDB, corrupting the PMU state. Windows always uses the PMU so this
> can cause adverse effects on that particular OS.
> 
> This series also contains patch "KVM: arm64: PMU: Set raw values from
> user to PM{C,I}NTEN{SET,CLR}, PMOVS{SET,CLR}", which reverts semantic
> changes made for the mentioned registers in the past. It is necessary
> to migrate the PMU state properly on Firecracker, QEMU, and crosvm.
> 
> Signed-off-by: Akihiko Odaki <[e-mail]>
> ---
> Changes in v5:
> - Rebased.
> - Link to v4: https://lore.kernel.org/r/[e-mail]
> 
> Changes in v4:
> - Reverted changes for functions implementing ioctls in patch
>   "KVM: arm64: PMU: Assume PMU presence in pmu-emul.c".
> - Removed kvm_pmu_vcpu_reset().
> - Reordered function calls in kvm_vcpu_reload_pmu() for better style.
> - Link to v3: https://lore.kernel.org/r/[e-mail]
> 
> Changes in v3:
> - Added patch "KVM: arm64: PMU: Assume PMU presence in pmu-emul.c".
> - Added an explanation of this path series' motivation to each patch.
> - Explained why userspace register writes and register reset should be
>   covered in patch "KVM: arm64: PMU: Reload when user modifies
>   registers".
> - Marked patch "KVM: arm64: PMU: Set raw values from user to
>   PM{C,I}NTEN{SET,CLR}, PMOVS{SET,CLR}" for stable.
> - Reoreded so that patch "KVM: arm64: PMU: Set raw values from user to
>   PM{C,I}NTEN{SET,CLR}, PMOVS{SET,CLR}" would come first.
> - Added patch "KVM: arm64: PMU: Call kvm_pmu_handle_pmcr() after masking
>   PMCNTENSET_EL0".
> - Added patch "KVM: arm64: Reload PMCNTENSET_EL0".
> - Link to v2: https://lore.kernel.org/r/[e-mail]
> 
> Changes in v2:
> - Changed to utilize KVM_REQ_RELOAD_PMU as suggested by Oliver Upton.
> - Added patch "KVM: arm64: PMU: Reload when user modifies registers"
>   to cover more registers.
> - Added patch "KVM: arm64: PMU: Set raw values from user to
>   PM{C,I}NTEN{SET,CLR}, PMOVS{SET,CLR}".
> - Link to v1: https://lore.kernel.org/r/[e-mail]
> 
> ---
> Akihiko Odaki (5):
>       KVM: arm64: PMU: Set raw values from user to PM{C,I}NTEN{SET,CLR}, PMOVS{SET,CLR}
>       KVM: arm64: PMU: Assume PMU presence in pmu-emul.c
>       KVM: arm64: PMU: Fix SET_ONE_REG for vPMC regs
>       KVM: arm64: PMU: Reload when user modifies registers
>       KVM: arm64: PMU: Reload when resetting
> 
>  arch/arm64/kvm/arm.c            | 17 ++++++++-----
>  arch/arm64/kvm/emulate-nested.c |  6 +++--
>  arch/arm64/kvm/pmu-emul.c       | 56 +++++++++++------------------------------
>  arch/arm64/kvm/reset.c          |  3 ---
>  arch/arm64/kvm/sys_regs.c       | 52 ++++++++++++++++++++++----------------
>  include/kvm/arm_pmu.h           |  4 +--
>  6 files changed, 62 insertions(+), 76 deletions(-)

Reviewed-by: Marc Zyngier <[e-mail]>

	M.