RISC-V: KVM: Add remote HFENCE functions based on VCPU requests

The generic KVM has support for VCPU requests which can be used
to do arch-specific work in the run-loop. We introduce remote
HFENCE functions which will internally use VCPU requests instead
of host SBI calls.

Advantages of doing remote HFENCEs as VCPU requests are:
1) Multiple VCPUs of a Guest may be running on different Host CPUs
   so it is not always possible to determine the Host CPU mask for
   doing Host SBI call. For example, when VCPU X wants to do HFENCE
   on VCPU Y, it is possible that VCPU Y is blocked or in user-space
   (i.e. vcpu->cpu < 0).
2) To support nested virtualization, we will be having a separate
   shadow G-stage for each VCPU and a common host G-stage for the
   entire Guest/VM. The VCPU requests based remote HFENCEs helps
   us easily synchronize the common host G-stage and shadow G-stage
   of each VCPU without any additional IPI calls.

This is also a preparatory patch for upcoming nested virtualization
support where we will be having a shadow G-stage page table for
each Guest VCPU.

Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Signed-off-by: Anup Patel <anup@brainfault.org>

1 files changed, 226 insertions, 1 deletions

diff --git a/arch/riscv/kvm/tlb.c b/arch/riscv/kvm/tlb.c
index e2d4fd610745..c0f86d09c41d 100644
--- a/arch/riscv/kvm/tlb.c
+++ b/arch/riscv/kvm/tlb.c
@@ -3,11 +3,14 @@
  * Copyright (c) 2022 Ventana Micro Systems Inc.
  */
 
-#include <linux/bitops.h>
+#include <linux/bitmap.h>
+#include <linux/cpumask.h>
 #include <linux/errno.h>
 #include <linux/err.h>
 #include <linux/module.h>
+#include <linux/smp.h>
 #include <linux/kvm_host.h>
+#include <asm/cacheflush.h>
 #include <asm/csr.h>
 
 /*
@@ -211,3 +214,225 @@ void kvm_riscv_local_hfence_vvma_all(unsigned long vmid)
 
 	csr_write(CSR_HGATP, hgatp);
 }
+
+void kvm_riscv_fence_i_process(struct kvm_vcpu *vcpu)
+{
+	local_flush_icache_all();
+}
+
+void kvm_riscv_hfence_gvma_vmid_all_process(struct kvm_vcpu *vcpu)
+{
+	struct kvm_vmid *vmid;
+
+	vmid = &vcpu->kvm->arch.vmid;
+	kvm_riscv_local_hfence_gvma_vmid_all(READ_ONCE(vmid->vmid));
+}
+
+void kvm_riscv_hfence_vvma_all_process(struct kvm_vcpu *vcpu)
+{
+	struct kvm_vmid *vmid;
+
+	vmid = &vcpu->kvm->arch.vmid;
+	kvm_riscv_local_hfence_vvma_all(READ_ONCE(vmid->vmid));
+}
+
+static bool vcpu_hfence_dequeue(struct kvm_vcpu *vcpu,
+				struct kvm_riscv_hfence *out_data)
+{
+	bool ret = false;
+	struct kvm_vcpu_arch *varch = &vcpu->arch;
+
+	spin_lock(&varch->hfence_lock);
+
+	if (varch->hfence_queue[varch->hfence_head].type) {
+		memcpy(out_data, &varch->hfence_queue[varch->hfence_head],
+		       sizeof(*out_data));
+		varch->hfence_queue[varch->hfence_head].type = 0;
+
+		varch->hfence_head++;
+		if (varch->hfence_head == KVM_RISCV_VCPU_MAX_HFENCE)
+			varch->hfence_head = 0;
+
+		ret = true;
+	}
+
+	spin_unlock(&varch->hfence_lock);
+
+	return ret;
+}
+
+static bool vcpu_hfence_enqueue(struct kvm_vcpu *vcpu,
+				const struct kvm_riscv_hfence *data)
+{
+	bool ret = false;
+	struct kvm_vcpu_arch *varch = &vcpu->arch;
+
+	spin_lock(&varch->hfence_lock);
+
+	if (!varch->hfence_queue[varch->hfence_tail].type) {
+		memcpy(&varch->hfence_queue[varch->hfence_tail],
+		       data, sizeof(*data));
+
+		varch->hfence_tail++;
+		if (varch->hfence_tail == KVM_RISCV_VCPU_MAX_HFENCE)
+			varch->hfence_tail = 0;
+
+		ret = true;
+	}
+
+	spin_unlock(&varch->hfence_lock);
+
+	return ret;
+}
+
+void kvm_riscv_hfence_process(struct kvm_vcpu *vcpu)
+{
+	struct kvm_riscv_hfence d = { 0 };
+	struct kvm_vmid *v = &vcpu->kvm->arch.vmid;
+
+	while (vcpu_hfence_dequeue(vcpu, &d)) {
+		switch (d.type) {
+		case KVM_RISCV_HFENCE_UNKNOWN:
+			break;
+		case KVM_RISCV_HFENCE_GVMA_VMID_GPA:
+			kvm_riscv_local_hfence_gvma_vmid_gpa(
+						READ_ONCE(v->vmid),
+						d.addr, d.size, d.order);
+			break;
+		case KVM_RISCV_HFENCE_VVMA_ASID_GVA:
+			kvm_riscv_local_hfence_vvma_asid_gva(
+						READ_ONCE(v->vmid), d.asid,
+						d.addr, d.size, d.order);
+			break;
+		case KVM_RISCV_HFENCE_VVMA_ASID_ALL:
+			kvm_riscv_local_hfence_vvma_asid_all(
+						READ_ONCE(v->vmid), d.asid);
+			break;
+		case KVM_RISCV_HFENCE_VVMA_GVA:
+			kvm_riscv_local_hfence_vvma_gva(
+						READ_ONCE(v->vmid),
+						d.addr, d.size, d.order);
+			break;
+		default:
+			break;
+		}
+	}
+}
+
+static void make_xfence_request(struct kvm *kvm,
+				unsigned long hbase, unsigned long hmask,
+				unsigned int req, unsigned int fallback_req,
+				const struct kvm_riscv_hfence *data)
+{
+	unsigned long i;
+	struct kvm_vcpu *vcpu;
+	unsigned int actual_req = req;
+	DECLARE_BITMAP(vcpu_mask, KVM_MAX_VCPUS);
+
+	bitmap_clear(vcpu_mask, 0, KVM_MAX_VCPUS);
+	kvm_for_each_vcpu(i, vcpu, kvm) {
+		if (hbase != -1UL) {
+			if (vcpu->vcpu_id < hbase)
+				continue;
+			if (!(hmask & (1UL << (vcpu->vcpu_id - hbase))))
+				continue;
+		}
+
+		bitmap_set(vcpu_mask, i, 1);
+
+		if (!data || !data->type)
+			continue;
+
+		/*
+		 * Enqueue hfence data to VCPU hfence queue. If we don't
+		 * have space in the VCPU hfence queue then fallback to
+		 * a more conservative hfence request.
+		 */
+		if (!vcpu_hfence_enqueue(vcpu, data))
+			actual_req = fallback_req;
+	}
+
+	kvm_make_vcpus_request_mask(kvm, actual_req, vcpu_mask);
+}
+
+void kvm_riscv_fence_i(struct kvm *kvm,
+		       unsigned long hbase, unsigned long hmask)
+{
+	make_xfence_request(kvm, hbase, hmask, KVM_REQ_FENCE_I,
+			    KVM_REQ_FENCE_I, NULL);
+}
+
+void kvm_riscv_hfence_gvma_vmid_gpa(struct kvm *kvm,
+				    unsigned long hbase, unsigned long hmask,
+				    gpa_t gpa, gpa_t gpsz,
+				    unsigned long order)
+{
+	struct kvm_riscv_hfence data;
+
+	data.type = KVM_RISCV_HFENCE_GVMA_VMID_GPA;
+	data.asid = 0;
+	data.addr = gpa;
+	data.size = gpsz;
+	data.order = order;
+	make_xfence_request(kvm, hbase, hmask, KVM_REQ_HFENCE,
+			    KVM_REQ_HFENCE_GVMA_VMID_ALL, &data);
+}
+
+void kvm_riscv_hfence_gvma_vmid_all(struct kvm *kvm,
+				    unsigned long hbase, unsigned long hmask)
+{
+	make_xfence_request(kvm, hbase, hmask, KVM_REQ_HFENCE_GVMA_VMID_ALL,
+			    KVM_REQ_HFENCE_GVMA_VMID_ALL, NULL);
+}
+
+void kvm_riscv_hfence_vvma_asid_gva(struct kvm *kvm,
+				    unsigned long hbase, unsigned long hmask,
+				    unsigned long gva, unsigned long gvsz,
+				    unsigned long order, unsigned long asid)
+{
+	struct kvm_riscv_hfence data;
+
+	data.type = KVM_RISCV_HFENCE_VVMA_ASID_GVA;
+	data.asid = asid;
+	data.addr = gva;
+	data.size = gvsz;
+	data.order = order;
+	make_xfence_request(kvm, hbase, hmask, KVM_REQ_HFENCE,
+			    KVM_REQ_HFENCE_VVMA_ALL, &data);
+}
+
+void kvm_riscv_hfence_vvma_asid_all(struct kvm *kvm,
+				    unsigned long hbase, unsigned long hmask,
+				    unsigned long asid)
+{
+	struct kvm_riscv_hfence data;
+
+	data.type = KVM_RISCV_HFENCE_VVMA_ASID_ALL;
+	data.asid = asid;
+	data.addr = data.size = data.order = 0;
+	make_xfence_request(kvm, hbase, hmask, KVM_REQ_HFENCE,
+			    KVM_REQ_HFENCE_VVMA_ALL, &data);
+}
+
+void kvm_riscv_hfence_vvma_gva(struct kvm *kvm,
+			       unsigned long hbase, unsigned long hmask,
+			       unsigned long gva, unsigned long gvsz,
+			       unsigned long order)
+{
+	struct kvm_riscv_hfence data;
+
+	data.type = KVM_RISCV_HFENCE_VVMA_GVA;
+	data.asid = 0;
+	data.addr = gva;
+	data.size = gvsz;
+	data.order = order;
+	make_xfence_request(kvm, hbase, hmask, KVM_REQ_HFENCE,
+			    KVM_REQ_HFENCE_VVMA_ALL, &data);
+}
+
+void kvm_riscv_hfence_vvma_all(struct kvm *kvm,
+			       unsigned long hbase, unsigned long hmask)
+{
+	make_xfence_request(kvm, hbase, hmask, KVM_REQ_HFENCE_VVMA_ALL,
+			    KVM_REQ_HFENCE_VVMA_ALL, NULL);
+}