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 akihiko.odaki@daynix.com --- Changes in v5: - Rebased. - Link to v4: https://lore.kernel.org/r/20250313-pmc-v4-0-2c976827118c@daynix.com
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/20250312-pmc-v3-0-0411cab5dc3d@daynix.com
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/20250307-pmc-v2-0-6c3375a5f1e4@daynix.com
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/20250302-pmc-v1-1-caff989093dc@daynix.com
--- 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,
Commit a45f41d754e0 ("KVM: arm64: Add {get,set}_user for PM{C,I}NTEN{SET,CLR}, PMOVS{SET,CLR}") changed KVM_SET_ONE_REG to update the mentioned registers in a way matching with the behavior of guest register writes. This is a breaking change of a UAPI though the new semantics looks cleaner and VMMs are not prepared for this.
Firecracker, QEMU, and crosvm perform migration by listing registers with KVM_GET_REG_LIST, getting their values with KVM_GET_ONE_REG and setting them with KVM_SET_ONE_REG. This algorithm assumes KVM_SET_ONE_REG restores the values retrieved with KVM_GET_ONE_REG without any alteration. However, bit operations added by the earlier commit do not preserve the values retried with KVM_GET_ONE_REG and potentially break migration.
Remove the bit operations that alter the values retrieved with KVM_GET_ONE_REG.
Cc: stable@vger.kernel.org Fixes: a45f41d754e0 ("KVM: arm64: Add {get,set}_user for PM{C,I}NTEN{SET,CLR}, PMOVS{SET,CLR}") Signed-off-by: Akihiko Odaki akihiko.odaki@daynix.com Acked-by: Marc Zyngier maz@kernel.org --- arch/arm64/kvm/sys_regs.c | 21 ++------------------- 1 file changed, 2 insertions(+), 19 deletions(-)
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c index 82430c1e1dd0..ffee72fd1273 100644 --- a/arch/arm64/kvm/sys_regs.c +++ b/arch/arm64/kvm/sys_regs.c @@ -1051,26 +1051,9 @@ static bool access_pmu_evtyper(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
static int set_pmreg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r, u64 val) { - bool set; - - val &= kvm_pmu_accessible_counter_mask(vcpu); - - switch (r->reg) { - case PMOVSSET_EL0: - /* CRm[1] being set indicates a SET register, and CLR otherwise */ - set = r->CRm & 2; - break; - default: - /* Op2[0] being set indicates a SET register, and CLR otherwise */ - set = r->Op2 & 1; - break; - } - - if (set) - __vcpu_sys_reg(vcpu, r->reg) |= val; - else - __vcpu_sys_reg(vcpu, r->reg) &= ~val; + u64 mask = kvm_pmu_accessible_counter_mask(vcpu);
+ __vcpu_sys_reg(vcpu, r->reg) = val & mask; return 0; }
On Sat, 15 Mar 2025 09:12:09 +0000, Akihiko Odaki akihiko.odaki@daynix.com 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 akihiko.odaki@daynix.com
Changes in v5:
- Rebased.
- Link to v4: https://lore.kernel.org/r/20250313-pmc-v4-0-2c976827118c@daynix.com
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/20250312-pmc-v3-0-0411cab5dc3d@daynix.com
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/20250307-pmc-v2-0-6c3375a5f1e4@daynix.com
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/20250302-pmc-v1-1-caff989093dc@daynix.com
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 maz@kernel.org
M.
On Sat, 15 Mar 2025 18:12:09 +0900, Akihiko Odaki 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.
[...]
Squashed in a fix for CONFIG_HW_PERF_EVENTS=n build.
Applied to next, thanks!
[1/5] KVM: arm64: PMU: Set raw values from user to PM{C,I}NTEN{SET,CLR}, PMOVS{SET,CLR} https://git.kernel.org/kvmarm/kvmarm/c/f2aeb7bbd574 [2/5] KVM: arm64: PMU: Assume PMU presence in pmu-emul.c https://git.kernel.org/kvmarm/kvmarm/c/be5ccac3f15e [3/5] KVM: arm64: PMU: Fix SET_ONE_REG for vPMC regs https://git.kernel.org/kvmarm/kvmarm/c/64074ca8ca92 [4/5] KVM: arm64: PMU: Reload when user modifies registers https://git.kernel.org/kvmarm/kvmarm/c/1db4aaa05589 [5/5] KVM: arm64: PMU: Reload when resetting https://git.kernel.org/kvmarm/kvmarm/c/fe53538069bb
-- Best, Oliver
linux-stable-mirror@lists.linaro.org
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Akihiko Odaki -
Marc Zyngier -
Oliver Upton