[PATCH v5 08/12] KVM: arm64: PMU: Allow userspace to limit PMCR_EL0.N for the guest

[Raghavendra Rao Ananta]

From: Reiji Watanabe <reijiw at google.com>

KVM does not yet support userspace modifying PMCR_EL0.N (With
the previous patch, KVM ignores what is written by upserspace).
Add support userspace limiting PMCR_EL0.N.

Disallow userspace to set PMCR_EL0.N to a value that is greater
than the host value (KVM_SET_ONE_REG will fail), as KVM doesn't
support more event counters than the host HW implements.
Although this is an ABI change, this change only affects
userspace setting PMCR_EL0.N to a larger value than the host.
As accesses to unadvertised event counters indices is CONSTRAINED
UNPREDICTABLE behavior, and PMCR_EL0.N was reset to the host value
on every vCPU reset before this series, I can't think of any
use case where a user space would do that.

Also, ignore writes to read-only bits that are cleared on vCPU reset,
and RES{0,1} bits (including writable bits that KVM doesn't support
yet), as those bits shouldn't be modified (at least with
the current KVM).

Signed-off-by: Reiji Watanabe <reijiw at google.com>
Signed-off-by: Raghavendra Rao Ananta <rananta at google.com>
---
 arch/arm64/include/asm/kvm_host.h |  3 ++
 arch/arm64/kvm/pmu-emul.c         |  1 +
 arch/arm64/kvm/sys_regs.c         | 49 +++++++++++++++++++++++++++++--
 3 files changed, 51 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 0f2dbbe8f6a7e..c15ec365283d1 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -259,6 +259,9 @@ struct kvm_arch {
 	/* PMCR_EL0.N value for the guest */
 	u8 pmcr_n;
 
+	/* Limit value of PMCR_EL0.N for the guest */
+	u8 pmcr_n_limit;
+
 	/* Hypercall features firmware registers' descriptor */
 	struct kvm_smccc_features smccc_feat;
 	struct maple_tree smccc_filter;
diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
index ce7de6bbdc967..39ad56a71ad20 100644
--- a/arch/arm64/kvm/pmu-emul.c
+++ b/arch/arm64/kvm/pmu-emul.c
@@ -896,6 +896,7 @@ int kvm_arm_set_vm_pmu(struct kvm *kvm, struct arm_pmu *arm_pmu)
 	 * while the latter does not.
 	 */
 	kvm->arch.pmcr_n = arm_pmu->num_events - 1;
+	kvm->arch.pmcr_n_limit = arm_pmu->num_events - 1;
 
 	return 0;
 }
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 2075901356c5b..c01d62afa7db4 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1086,6 +1086,51 @@ static int get_pmcr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r,
 	return 0;
 }
 
+static int set_pmcr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r,
+		    u64 val)
+{
+	struct kvm *kvm = vcpu->kvm;
+	u64 new_n, mutable_mask;
+	int ret = 0;
+
+	new_n = FIELD_GET(ARMV8_PMU_PMCR_N, val);
+
+	mutex_lock(&kvm->arch.config_lock);
+	if (unlikely(new_n != kvm->arch.pmcr_n)) {
+		/*
+		 * The vCPU can't have more counters than the PMU
+		 * hardware implements.
+		 */
+		if (new_n <= kvm->arch.pmcr_n_limit)
+			kvm->arch.pmcr_n = new_n;
+		else
+			ret = -EINVAL;
+	}
+	mutex_unlock(&kvm->arch.config_lock);
+	if (ret)
+		return ret;
+
+	/*
+	 * Ignore writes to RES0 bits, read only bits that are cleared on
+	 * vCPU reset, and writable bits that KVM doesn't support yet.
+	 * (i.e. only PMCR.N and bits [7:0] are mutable from userspace)
+	 * The LP bit is RES0 when FEAT_PMUv3p5 is not supported on the vCPU.
+	 * But, we leave the bit as it is here, as the vCPU's PMUver might
+	 * be changed later (NOTE: the bit will be cleared on first vCPU run
+	 * if necessary).
+	 */
+	mutable_mask = (ARMV8_PMU_PMCR_MASK | ARMV8_PMU_PMCR_N);
+	val &= mutable_mask;
+	val |= (__vcpu_sys_reg(vcpu, r->reg) & ~mutable_mask);
+
+	/* The LC bit is RES1 when AArch32 is not supported */
+	if (!kvm_supports_32bit_el0())
+		val |= ARMV8_PMU_PMCR_LC;
+
+	__vcpu_sys_reg(vcpu, r->reg) = val;
+	return 0;
+}
+
 /* Silly macro to expand the DBG{BCR,BVR,WVR,WCR}n_EL1 registers in one go */
 #define DBG_BCR_BVR_WCR_WVR_EL1(n)					\
 	{ SYS_DESC(SYS_DBGBVRn_EL1(n)),					\
@@ -2147,8 +2192,8 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 	{ SYS_DESC(SYS_CTR_EL0), access_ctr },
 	{ SYS_DESC(SYS_SVCR), undef_access },
 
-	{ PMU_SYS_REG(PMCR_EL0), .access = access_pmcr,
-	  .reset = reset_pmcr, .reg = PMCR_EL0, .get_user = get_pmcr },
+	{ PMU_SYS_REG(PMCR_EL0), .access = access_pmcr, .reset = reset_pmcr,
+	  .reg = PMCR_EL0, .get_user = get_pmcr, .set_user = set_pmcr },
 	{ PMU_SYS_REG(PMCNTENSET_EL0),
 	  .access = access_pmcnten, .reg = PMCNTENSET_EL0 },
 	{ PMU_SYS_REG(PMCNTENCLR_EL0),
-- 
2.41.0.694.ge786442a9b-goog