linux-kernel - [PATCH 1/2] RISC-V: KVM: Enable ring-based dirty memory tracking

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Message-Id: <20e116efb1f7aff211dd8e3cf8990c5521ed5f34.1749810735.git.zhouquan@iscas.ac.cn>
Date: Fri, 13 Jun 2025 19:29:57 +0800
From: zhouquan@...as.ac.cn
To: anup@...infault.org,
	ajones@...tanamicro.com,
	atishp@...shpatra.org,
	paul.walmsley@...ive.com,
	palmer@...belt.com
Cc: linux-kernel@...r.kernel.org,
	linux-riscv@...ts.infradead.org,
	kvm@...r.kernel.org,
	kvm-riscv@...ts.infradead.org,
	Quan Zhou <zhouquan@...as.ac.cn>
Subject: [PATCH 1/2] RISC-V: KVM: Enable ring-based dirty memory tracking

From: Quan Zhou <zhouquan@...as.ac.cn>

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@...as.ac.cn>
---
 Documentation/virt/kvm/api.rst    |  2 +-
 arch/riscv/include/uapi/asm/kvm.h |  1 +
 arch/riscv/kvm/Kconfig            |  1 +
 arch/riscv/kvm/vcpu.c             | 18 ++++++++++++++++--
 4 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 1bd2d42e6424..5de0fbfe2fc0 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -8316,7 +8316,7 @@ 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
 
diff --git a/arch/riscv/include/uapi/asm/kvm.h b/arch/riscv/include/uapi/asm/kvm.h
index 5f59fd226cc5..ef27d4289da1 100644
--- a/arch/riscv/include/uapi/asm/kvm.h
+++ b/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
diff --git a/arch/riscv/kvm/Kconfig b/arch/riscv/kvm/Kconfig
index 704c2899197e..5a62091b0809 100644
--- a/arch/riscv/kvm/Kconfig
+++ b/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
diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
index e0a01af426ff..0502125efb30 100644
--- a/arch/riscv/kvm/vcpu.c
+++ b/arch/riscv/kvm/vcpu.c
@@ -690,7 +690,14 @@ 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);
 
@@ -735,7 +742,12 @@ 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)
@@ -917,7 +929,9 @@ 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();
 
-- 
2.34.1