linux-kernel - [PATCH v7 36/45] arm64: RME: Set breakpoint parameters through SET_ONE

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Message-ID: <20250213161426.102987-37-steven.price@arm.com>
Date: Thu, 13 Feb 2025 16:14:16 +0000
From: Steven Price <steven.price@....com>
To: kvm@...r.kernel.org,
	kvmarm@...ts.linux.dev
Cc: Jean-Philippe Brucker <jean-philippe@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Marc Zyngier <maz@...nel.org>,
	Will Deacon <will@...nel.org>,
	James Morse <james.morse@....com>,
	Oliver Upton <oliver.upton@...ux.dev>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Joey Gouly <joey.gouly@....com>,
	Alexandru Elisei <alexandru.elisei@....com>,
	Christoffer Dall <christoffer.dall@....com>,
	Fuad Tabba <tabba@...gle.com>,
	linux-coco@...ts.linux.dev,
	Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>,
	Gavin Shan <gshan@...hat.com>,
	Shanker Donthineni <sdonthineni@...dia.com>,
	Alper Gun <alpergun@...gle.com>,
	"Aneesh Kumar K . V" <aneesh.kumar@...nel.org>,
	Steven Price <steven.price@....com>
Subject: [PATCH v7 36/45] arm64: RME: Set breakpoint parameters through SET_ONE_REG

From: Jean-Philippe Brucker <jean-philippe@...aro.org>

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 <jean-philippe@...aro.org>
Signed-off-by: Steven Price <steven.price@....com>
---
 arch/arm64/kvm/guest.c    |  2 ++
 arch/arm64/kvm/rme.c      |  3 +++
 arch/arm64/kvm/sys_regs.c | 17 +++++++++++------
 3 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
index da8961a5d01a..dbd45d0a0d54 100644
--- a/arch/arm64/kvm/guest.c
+++ b/arch/arm64/kvm/guest.c
@@ -802,6 +802,7 @@ 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 some GPRs and PC. The selection of GPRs
@@ -820,6 +821,7 @@ 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 8c426f575728..f236e1776d8c 100644
--- a/arch/arm64/kvm/rme.c
+++ b/arch/arm64/kvm/rme.c
@@ -355,6 +355,7 @@ static int realm_create_rd(struct kvm *kvm)
 	void *rd = NULL;
 	phys_addr_t rd_phys, params_phys;
 	size_t pgd_size = kvm_pgtable_stage2_pgd_size(kvm->arch.mmu.vtcr);
+	u64 dfr0 = kvm_read_vm_id_reg(kvm, SYS_ID_AA64DFR0_EL1);
 	int i, r;
 	int rtt_num_start;
 
@@ -391,6 +392,8 @@ static int realm_create_rd(struct kvm *kvm)
 	params->rtt_num_start = rtt_num_start;
 	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 5618eff33155..efd86df4e59d 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1829,6 +1829,9 @@ 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
@@ -1848,10 +1851,11 @@ 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);
@@ -1998,10 +2002,11 @@ 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
-- 
2.43.0