RISC-V: KVM: Enable ring-based dirty memory tracking

Enable ring-based dirty memory tracking on riscv:

- Enable CONFIG_HAVE_KVM_DIRTY_RING_ACQ_REL as riscv is weakly
  ordered.
- Set KVM_DIRTY_LOG_PAGE_OFFSET for the ring buffer's physical page
  offset.
- Add a check to kvm_vcpu_kvm_riscv_check_vcpu_requests for checking
  whether the dirty ring is soft full.

To handle vCPU requests that cause exits to userspace, modified the
`kvm_riscv_check_vcpu_requests` to return a value (currently only
returns 0 or 1).

Signed-off-by: Quan Zhou <zhouquan@iscas.ac.cn>
Reviewed-by: Anup Patel <anup@brainfault.org>
Link: https://lore.kernel.org/r/20e116efb1f7aff211dd8e3cf8990c5521ed5f34.1749810735.git.zhouquan@iscas.ac.cn
Signed-off-by: Anup Patel <anup@brainfault.org>

Documentation/virt/kvm/api.rst

@@ -8373,7 +8373,7 @@ core crystal clock frequency, if a non-zero CPUID 0x15 is exposed to the guest.
 7.36 KVM_CAP_DIRTY_LOG_RING/KVM_CAP_DIRTY_LOG_RING_ACQ_REL
 ----------------------------------------------------------
 
-:Architectures: x86, arm64
+:Architectures: x86, arm64, riscv
 :Type: vm
 :Parameters: args[0] - size of the dirty log ring
 

arch/riscv/include/uapi/asm/kvm.h

@@ -18,6 +18,7 @@
 #define __KVM_HAVE_IRQ_LINE
 
 #define KVM_COALESCED_MMIO_PAGE_OFFSET 1
+#define KVM_DIRTY_LOG_PAGE_OFFSET 64
 
 #define KVM_INTERRUPT_SET	-1U
 #define KVM_INTERRUPT_UNSET	-2U

arch/riscv/kvm/Kconfig

@@ -25,6 +25,7 @@ config KVM
 	select HAVE_KVM_MSI
 	select HAVE_KVM_VCPU_ASYNC_IOCTL
 	select HAVE_KVM_READONLY_MEM
+	select HAVE_KVM_DIRTY_RING_ACQ_REL
 	select KVM_COMMON
 	select KVM_GENERIC_DIRTYLOG_READ_PROTECT
 	select KVM_GENERIC_HARDWARE_ENABLING

arch/riscv/kvm/vcpu.c

@@ -682,7 +682,14 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
 	}
 }
 
-static void kvm_riscv_check_vcpu_requests(struct kvm_vcpu *vcpu)
+/**
+ * check_vcpu_requests - check and handle pending vCPU requests
+ * @vcpu:	the VCPU pointer
+ *
+ * Return: 1 if we should enter the guest
+ *	    0 if we should exit to userspace
+ */
+static int kvm_riscv_check_vcpu_requests(struct kvm_vcpu *vcpu)
 {
 	struct rcuwait *wait = kvm_arch_vcpu_get_wait(vcpu);
 
@@ -723,7 +730,12 @@ static void kvm_riscv_check_vcpu_requests(struct kvm_vcpu *vcpu)
 
 		if (kvm_check_request(KVM_REQ_STEAL_UPDATE, vcpu))
 			kvm_riscv_vcpu_record_steal_time(vcpu);
+
+		if (kvm_dirty_ring_check_request(vcpu))
+			return 0;
 	}
+
+	return 1;
 }
 
 static void kvm_riscv_update_hvip(struct kvm_vcpu *vcpu)
@@ -905,7 +917,9 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
 
 		kvm_riscv_gstage_vmid_update(vcpu);
 
-		kvm_riscv_check_vcpu_requests(vcpu);
+		ret = kvm_riscv_check_vcpu_requests(vcpu);
+		if (ret <= 0)
+			continue;
 
 		preempt_disable();