RISC-V: KVM: Implement SBI PMU Snapshot feature

PMU Snapshot function allows to minimize the number of traps when the
guest access configures/access the hpmcounters. If the snapshot feature
is enabled, the hypervisor updates the shared memory with counter
data and state of overflown counters. The guest can just read the
shared memory instead of trap & emulate done by the hypervisor.

This patch doesn't implement the counter overflow yet.

Reviewed-by: Anup Patel <anup@brainfault.org>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Signed-off-by: Atish Patra <atishp@rivosinc.com>
Link: https://lore.kernel.org/r/20240420151741.962500-14-atishp@rivosinc.com
Signed-off-by: Anup Patel <anup@brainfault.org>

Author: atishp04

arch/riscv/include/asm/kvm_vcpu_pmu.h

@@ -50,6 +50,10 @@ struct kvm_pmu {
 	bool init_done;
 	/* Bit map of all the virtual counter used */
 	DECLARE_BITMAP(pmc_in_use, RISCV_KVM_MAX_COUNTERS);
+	/* The address of the counter snapshot area (guest physical address) */
+	gpa_t snapshot_addr;
+	/* The actual data of the snapshot */
+	struct riscv_pmu_snapshot_data *sdata;
 };
 
 #define vcpu_to_pmu(vcpu) (&(vcpu)->arch.pmu_context)
@@ -85,6 +89,9 @@ int kvm_riscv_vcpu_pmu_ctr_cfg_match(struct kvm_vcpu *vcpu, unsigned long ctr_ba
 int kvm_riscv_vcpu_pmu_ctr_read(struct kvm_vcpu *vcpu, unsigned long cidx,
 				struct kvm_vcpu_sbi_return *retdata);
 void kvm_riscv_vcpu_pmu_init(struct kvm_vcpu *vcpu);
+int kvm_riscv_vcpu_pmu_snapshot_set_shmem(struct kvm_vcpu *vcpu, unsigned long saddr_low,
+				      unsigned long saddr_high, unsigned long flags,
+				      struct kvm_vcpu_sbi_return *retdata);
 void kvm_riscv_vcpu_pmu_deinit(struct kvm_vcpu *vcpu);
 void kvm_riscv_vcpu_pmu_reset(struct kvm_vcpu *vcpu);
 

arch/riscv/kvm/vcpu_pmu.c

@@ -14,6 +14,7 @@
 #include <asm/csr.h>
 #include <asm/kvm_vcpu_sbi.h>
 #include <asm/kvm_vcpu_pmu.h>
+#include <asm/sbi.h>
 #include <linux/bitops.h>
 
 #define kvm_pmu_num_counters(pmu) ((pmu)->num_hw_ctrs + (pmu)->num_fw_ctrs)
@@ -311,6 +312,80 @@ int kvm_riscv_vcpu_pmu_read_hpm(struct kvm_vcpu *vcpu, unsigned int csr_num,
 	return ret;
 }
 
+static void kvm_pmu_clear_snapshot_area(struct kvm_vcpu *vcpu)
+{
+	struct kvm_pmu *kvpmu = vcpu_to_pmu(vcpu);
+	int snapshot_area_size = sizeof(struct riscv_pmu_snapshot_data);
+
+	if (kvpmu->sdata) {
+		if (kvpmu->snapshot_addr != INVALID_GPA) {
+			memset(kvpmu->sdata, 0, snapshot_area_size);
+			kvm_vcpu_write_guest(vcpu, kvpmu->snapshot_addr,
+					     kvpmu->sdata, snapshot_area_size);
+		} else {
+			pr_warn("snapshot address invalid\n");
+		}
+		kfree(kvpmu->sdata);
+		kvpmu->sdata = NULL;
+	}
+	kvpmu->snapshot_addr = INVALID_GPA;
+}
+
+int kvm_riscv_vcpu_pmu_snapshot_set_shmem(struct kvm_vcpu *vcpu, unsigned long saddr_low,
+				      unsigned long saddr_high, unsigned long flags,
+				      struct kvm_vcpu_sbi_return *retdata)
+{
+	struct kvm_pmu *kvpmu = vcpu_to_pmu(vcpu);
+	int snapshot_area_size = sizeof(struct riscv_pmu_snapshot_data);
+	int sbiret = 0;
+	gpa_t saddr;
+	unsigned long hva;
+	bool writable;
+
+	if (!kvpmu || flags) {
+		sbiret = SBI_ERR_INVALID_PARAM;
+		goto out;
+	}
+
+	if (saddr_low == SBI_SHMEM_DISABLE && saddr_high == SBI_SHMEM_DISABLE) {
+		kvm_pmu_clear_snapshot_area(vcpu);
+		return 0;
+	}
+
+	saddr = saddr_low;
+
+	if (saddr_high != 0) {
+		if (IS_ENABLED(CONFIG_32BIT))
+			saddr |= ((gpa_t)saddr_high << 32);
+		else
+			sbiret = SBI_ERR_INVALID_ADDRESS;
+		goto out;
+	}
+
+	hva = kvm_vcpu_gfn_to_hva_prot(vcpu, saddr >> PAGE_SHIFT, &writable);
+	if (kvm_is_error_hva(hva) || !writable) {
+		sbiret = SBI_ERR_INVALID_ADDRESS;
+		goto out;
+	}
+
+	kvpmu->sdata = kzalloc(snapshot_area_size, GFP_ATOMIC);
+	if (!kvpmu->sdata)
+		return -ENOMEM;
+
+	if (kvm_vcpu_write_guest(vcpu, saddr, kvpmu->sdata, snapshot_area_size)) {
+		kfree(kvpmu->sdata);
+		sbiret = SBI_ERR_FAILURE;
+		goto out;
+	}
+
+	kvpmu->snapshot_addr = saddr;
+
+out:
+	retdata->err_val = sbiret;
+
+	return 0;
+}
+
 int kvm_riscv_vcpu_pmu_num_ctrs(struct kvm_vcpu *vcpu,
 				struct kvm_vcpu_sbi_return *retdata)
 {
@@ -344,20 +419,38 @@ int kvm_riscv_vcpu_pmu_ctr_start(struct kvm_vcpu *vcpu, unsigned long ctr_base,
 	int i, pmc_index, sbiret = 0;
 	struct kvm_pmc *pmc;
 	int fevent_code;
+	bool snap_flag_set = flags & SBI_PMU_START_FLAG_INIT_SNAPSHOT;
 
 	if (kvm_pmu_validate_counter_mask(kvpmu, ctr_base, ctr_mask) < 0) {
 		sbiret = SBI_ERR_INVALID_PARAM;
 		goto out;
 	}
 
+	if (snap_flag_set) {
+		if (kvpmu->snapshot_addr == INVALID_GPA) {
+			sbiret = SBI_ERR_NO_SHMEM;
+			goto out;
+		}
+		if (kvm_vcpu_read_guest(vcpu, kvpmu->snapshot_addr, kvpmu->sdata,
+					sizeof(struct riscv_pmu_snapshot_data))) {
+			pr_warn("Unable to read snapshot shared memory while starting counters\n");
+			sbiret = SBI_ERR_FAILURE;
+			goto out;
+		}
+	}
 	/* Start the counters that have been configured and requested by the guest */
 	for_each_set_bit(i, &ctr_mask, RISCV_MAX_COUNTERS) {
 		pmc_index = i + ctr_base;
 		if (!test_bit(pmc_index, kvpmu->pmc_in_use))
 			continue;
 		pmc = &kvpmu->pmc[pmc_index];
-		if (flags & SBI_PMU_START_FLAG_SET_INIT_VALUE)
+		if (flags & SBI_PMU_START_FLAG_SET_INIT_VALUE) {
 			pmc->counter_val = ival;
+		} else if (snap_flag_set) {
+			/* The counter index in the snapshot are relative to the counter base */
+			pmc->counter_val = kvpmu->sdata->ctr_values[i];
+		}
+
 		if (pmc->cinfo.type == SBI_PMU_CTR_TYPE_FW) {
 			fevent_code = get_event_code(pmc->event_idx);
 			if (fevent_code >= SBI_PMU_FW_MAX) {
@@ -398,14 +491,22 @@ int kvm_riscv_vcpu_pmu_ctr_stop(struct kvm_vcpu *vcpu, unsigned long ctr_base,
 {
 	struct kvm_pmu *kvpmu = vcpu_to_pmu(vcpu);
 	int i, pmc_index, sbiret = 0;
+	u64 enabled, running;
 	struct kvm_pmc *pmc;
 	int fevent_code;
+	bool snap_flag_set = flags & SBI_PMU_STOP_FLAG_TAKE_SNAPSHOT;
+	bool shmem_needs_update = false;
 
 	if (kvm_pmu_validate_counter_mask(kvpmu, ctr_base, ctr_mask) < 0) {
 		sbiret = SBI_ERR_INVALID_PARAM;
 		goto out;
 	}
 
+	if (snap_flag_set && kvpmu->snapshot_addr == INVALID_GPA) {
+		sbiret = SBI_ERR_NO_SHMEM;
+		goto out;
+	}
+
 	/* Stop the counters that have been configured and requested by the guest */
 	for_each_set_bit(i, &ctr_mask, RISCV_MAX_COUNTERS) {
 		pmc_index = i + ctr_base;
@@ -438,12 +539,28 @@ int kvm_riscv_vcpu_pmu_ctr_stop(struct kvm_vcpu *vcpu, unsigned long ctr_base,
 		} else {
 			sbiret = SBI_ERR_INVALID_PARAM;
 		}
+
+		if (snap_flag_set && !sbiret) {
+			if (pmc->cinfo.type == SBI_PMU_CTR_TYPE_FW)
+				pmc->counter_val = kvpmu->fw_event[fevent_code].value;
+			else if (pmc->perf_event)
+				pmc->counter_val += perf_event_read_value(pmc->perf_event,
+									  &enabled, &running);
+			/* TODO: Add counter overflow support when sscofpmf support is added */
+			kvpmu->sdata->ctr_values[i] = pmc->counter_val;
+			shmem_needs_update = true;
+		}
+
 		if (flags & SBI_PMU_STOP_FLAG_RESET) {
 			pmc->event_idx = SBI_PMU_EVENT_IDX_INVALID;
 			clear_bit(pmc_index, kvpmu->pmc_in_use);
 		}
 	}
 
+	if (shmem_needs_update)
+		kvm_vcpu_write_guest(vcpu, kvpmu->snapshot_addr, kvpmu->sdata,
+					     sizeof(struct riscv_pmu_snapshot_data));
+
 out:
 	retdata->err_val = sbiret;
 
@@ -566,6 +683,7 @@ void kvm_riscv_vcpu_pmu_init(struct kvm_vcpu *vcpu)
 	kvpmu->num_hw_ctrs = num_hw_ctrs + 1;
 	kvpmu->num_fw_ctrs = SBI_PMU_FW_MAX;
 	memset(&kvpmu->fw_event, 0, SBI_PMU_FW_MAX * sizeof(struct kvm_fw_event));
+	kvpmu->snapshot_addr = INVALID_GPA;
 
 	if (kvpmu->num_hw_ctrs > RISCV_KVM_MAX_HW_CTRS) {
 		pr_warn_once("Limiting the hardware counters to 32 as specified by the ISA");
@@ -625,6 +743,7 @@ void kvm_riscv_vcpu_pmu_deinit(struct kvm_vcpu *vcpu)
 	}
 	bitmap_zero(kvpmu->pmc_in_use, RISCV_MAX_COUNTERS);
 	memset(&kvpmu->fw_event, 0, SBI_PMU_FW_MAX * sizeof(struct kvm_fw_event));
+	kvm_pmu_clear_snapshot_area(vcpu);
 }
 
 void kvm_riscv_vcpu_pmu_reset(struct kvm_vcpu *vcpu)

arch/riscv/kvm/vcpu_sbi_pmu.c

@@ -64,6 +64,9 @@ static int kvm_sbi_ext_pmu_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
 	case SBI_EXT_PMU_COUNTER_FW_READ:
 		ret = kvm_riscv_vcpu_pmu_ctr_read(vcpu, cp->a0, retdata);
 		break;
+	case SBI_EXT_PMU_SNAPSHOT_SET_SHMEM:
+		ret = kvm_riscv_vcpu_pmu_snapshot_set_shmem(vcpu, cp->a0, cp->a1, cp->a2, retdata);
+		break;
 	default:
 		retdata->err_val = SBI_ERR_NOT_SUPPORTED;
 	}