[v4,36/43] arm64: RME: Set breakpoint parameters through SET_ONE_REG

Commit Message

Steven Price Aug. 21, 2024, 3:38 p.m. UTC

From: Jean-Philippe Brucker <[e-mail]>

Allow userspace to configure the number of breakpoints and watchpoints
of a Realm VM through KVM_SET_ONE_REG ID_AA64DFR0_EL1.

The KVM sys_reg handler checks the user value against the maximum value
given by RMM (arm64_check_features() gets it from the
read_sanitised_id_aa64dfr0_el1() reset handler).

Userspace discovers that it can write these fields by issuing a
KVM_ARM_GET_REG_WRITABLE_MASKS ioctl.

Signed-off-by: Jean-Philippe Brucker <[e-mail]>
Signed-off-by: Steven Price <[e-mail]>
---
 arch/arm64/kvm/guest.c    |  2 ++
 arch/arm64/kvm/rme.c      |  3 +++
 arch/arm64/kvm/sys_regs.c | 21 ++++++++++++++-------
 3 files changed, 19 insertions(+), 7 deletions(-)

Patch

diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
index 24d8220c1d67..b0cabba974b8 100644
--- a/arch/arm64/kvm/guest.c
+++ b/arch/arm64/kvm/guest.c
@@ -784,6 +784,7 @@  int kvm_arm_get_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
 }
 
 #define KVM_REG_ARM_PMCR_EL0		ARM64_SYS_REG(3, 3, 9, 12, 0)
+#define KVM_REG_ARM_ID_AA64DFR0_EL1	ARM64_SYS_REG(3, 0, 0, 5, 0)
 
 /*
  * The RMI ABI only enables setting the lower GPRs (x0-x7) and PC.
@@ -806,6 +807,7 @@  static bool validate_realm_set_reg(struct kvm_vcpu *vcpu,
 	} else {
 		switch (reg->id) {
 		case KVM_REG_ARM_PMCR_EL0:
+		case KVM_REG_ARM_ID_AA64DFR0_EL1:
 			return true;
 		}
 	}
diff --git a/arch/arm64/kvm/rme.c b/arch/arm64/kvm/rme.c
index 5d9f732f4df2..42f52b21bdae 100644
--- a/arch/arm64/kvm/rme.c
+++ b/arch/arm64/kvm/rme.c
@@ -315,6 +315,7 @@  static int realm_create_rd(struct kvm *kvm)
 	void *rd = NULL;
 	phys_addr_t rd_phys, params_phys;
 	struct kvm_pgtable *pgt = kvm->arch.mmu.pgt;
+	u64 dfr0 = kvm_read_vm_id_reg(kvm, SYS_ID_AA64DFR0_EL1);
 	int i, r;
 
 	if (WARN_ON(realm->rd) || WARN_ON(!realm->params))
@@ -346,6 +347,8 @@  static int realm_create_rd(struct kvm *kvm)
 	params->rtt_num_start = pgt->pgd_pages;
 	params->rtt_base = kvm->arch.mmu.pgd_phys;
 	params->vmid = realm->vmid;
+	params->num_bps = SYS_FIELD_GET(ID_AA64DFR0_EL1, BRPs, dfr0);
+	params->num_wps = SYS_FIELD_GET(ID_AA64DFR0_EL1, WRPs, dfr0);
 
 	if (kvm->arch.arm_pmu) {
 		params->pmu_num_ctrs = kvm->arch.pmcr_n;
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index c7a5b1a8a224..f92b78039dce 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1741,6 +1741,9 @@  static int set_id_aa64dfr0_el1(struct kvm_vcpu *vcpu,
 {
 	u8 debugver = SYS_FIELD_GET(ID_AA64DFR0_EL1, DebugVer, val);
 	u8 pmuver = SYS_FIELD_GET(ID_AA64DFR0_EL1, PMUVer, val);
+	u8 bps = SYS_FIELD_GET(ID_AA64DFR0_EL1, BRPs, val);
+	u8 wps = SYS_FIELD_GET(ID_AA64DFR0_EL1, WRPs, val);
+	u8 ctx_cmps = SYS_FIELD_GET(ID_AA64DFR0_EL1, CTX_CMPs, val);
 
 	/*
 	 * Prior to commit 3d0dba5764b9 ("KVM: arm64: PMU: Move the
@@ -1760,10 +1763,11 @@  static int set_id_aa64dfr0_el1(struct kvm_vcpu *vcpu,
 		val &= ~ID_AA64DFR0_EL1_PMUVer_MASK;
 
 	/*
-	 * ID_AA64DFR0_EL1.DebugVer is one of those awkward fields with a
-	 * nonzero minimum safe value.
+	 * ID_AA64DFR0_EL1.DebugVer, BRPs and WRPs all have to be greater than
+	 * zero. CTX_CMPs is never greater than BRPs.
 	 */
-	if (debugver < ID_AA64DFR0_EL1_DebugVer_IMP)
+	if (debugver < ID_AA64DFR0_EL1_DebugVer_IMP || !bps || !wps ||
+	    ctx_cmps > bps)
 		return -EINVAL;
 
 	return set_id_reg(vcpu, rd, val);
@@ -1846,10 +1850,11 @@  static int set_id_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd,
 	mutex_lock(&vcpu->kvm->arch.config_lock);
 
 	/*
-	 * Once the VM has started the ID registers are immutable. Reject any
-	 * write that does not match the final register value.
+	 * Once the VM has started or the Realm descriptor is created, the ID
+	 * registers are immutable. Reject any write that does not match the
+	 * final register value.
 	 */
-	if (kvm_vm_has_ran_once(vcpu->kvm)) {
+	if (kvm_vm_has_ran_once(vcpu->kvm) || kvm_realm_is_created(vcpu->kvm)) {
 		if (val != read_id_reg(vcpu, rd))
 			ret = -EBUSY;
 		else
@@ -2377,7 +2382,9 @@  static const struct sys_reg_desc sys_reg_descs[] = {
 	  .set_user = set_id_aa64dfr0_el1,
 	  .reset = read_sanitised_id_aa64dfr0_el1,
 	  .val = ID_AA64DFR0_EL1_PMUVer_MASK |
-		 ID_AA64DFR0_EL1_DebugVer_MASK, },
+		 ID_AA64DFR0_EL1_DebugVer_MASK |
+		 ID_AA64DFR0_EL1_BRPs_MASK |
+		 ID_AA64DFR0_EL1_WRPs_MASK, },
 	ID_SANITISED(ID_AA64DFR1_EL1),
 	ID_UNALLOCATED(5,2),
 	ID_UNALLOCATED(5,3),