linux-kernel - [PATCH v2] RISC-V: KVM: flush VS-stage TLB after VCPU migration to prevent stale entries

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Message-ID: <20251021083105.4029305-1-minachou@andestech.com>
Date: Tue, 21 Oct 2025 16:31:05 +0800
From: Hui Min Mina Chou <minachou@...estech.com>
To: <anup@...infault.org>, <atish.patra@...ux.dev>, <pjw@...nel.org>,
        <palmer@...belt.com>, <aou@...s.berkeley.edu>, <alex@...ti.fr>
CC: <kvm@...r.kernel.org>, <kvm-riscv@...ts.infradead.org>,
        <linux-riscv@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <tim609@...estech.com>, <minachou@...estech.com>,
        <ben717@...estech.com>, <az70021@...il.com>
Subject: [PATCH v2] RISC-V: KVM: flush VS-stage TLB after VCPU migration to prevent stale entries

From: Hui Min Mina Chou <minachou@...estech.com>

If multiple VCPUs of the same Guest/VM run on the same Host CPU,
hfence.vvma only flushes that Host CPU’s VS-stage TLB. Other Host CPUs
may retain stale VS-stage entries. When a VCPU later migrates to a
different Host CPU, it can hit these stale GVA to GPA mappings, causing
unexpected faults in the Guest.

To fix this, kvm_riscv_gstage_vmid_sanitize() is extended to flush both
G-stage and VS-stage TLBs whenever a VCPU migrates to a different Host CPU.
This ensures that no stale VS-stage mappings remain after VCPU migration.

Fixes: 92e450507d56 ("RISC-V: KVM: Cleanup stale TLB entries when host CPU changes")
Signed-off-by: Hui Min Mina Chou <minachou@...estech.com>
Signed-off-by: Ben Zong-You Xie <ben717@...estech.com>
---
Changes in v2:
- Updated Fixes commit to 92e450507d56
- Renamed function to kvm_riscv_local_tlb_sanitize

 arch/riscv/kvm/vmid.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/kvm/vmid.c b/arch/riscv/kvm/vmid.c
index 3b426c800480..6323f5383d36 100644
--- a/arch/riscv/kvm/vmid.c
+++ b/arch/riscv/kvm/vmid.c
@@ -125,7 +125,7 @@ void kvm_riscv_gstage_vmid_update(struct kvm_vcpu *vcpu)
 		kvm_make_request(KVM_REQ_UPDATE_HGATP, v);
 }
 
-void kvm_riscv_gstage_vmid_sanitize(struct kvm_vcpu *vcpu)
+void kvm_riscv_local_tlb_sanitize(struct kvm_vcpu *vcpu)
 {
 	unsigned long vmid;
 
@@ -146,4 +146,10 @@ void kvm_riscv_gstage_vmid_sanitize(struct kvm_vcpu *vcpu)
 
 	vmid = READ_ONCE(vcpu->kvm->arch.vmid.vmid);
 	kvm_riscv_local_hfence_gvma_vmid_all(vmid);
+
+	/*
+	 * Flush VS-stage TLBs entry after VCPU migration to avoid using
+	 * stale entries.
+	 */
+	kvm_riscv_local_hfence_vvma_all(vmid);
 }
-- 
2.34.1