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Message-Id: <20251118080656.2012805-2-maobibo@loongson.cn>
Date: Tue, 18 Nov 2025 16:06:54 +0800
From: Bibo Mao <maobibo@...ngson.cn>
To: Paolo Bonzini <pbonzini@...hat.com>,
Huacai Chen <chenhuacai@...nel.org>,
Tianrui Zhao <zhaotianrui@...ngson.cn>,
WANG Xuerui <kernel@...0n.name>
Cc: kvm@...r.kernel.org,
loongarch@...ts.linux.dev,
linux-kernel@...r.kernel.org
Subject: [PATCH 1/3] LoongArch: KVM: Add preempt hint feature in hypervisor side
Feature KVM_FEATURE_PREEMPT_HINT is added to show whether vCPU is
preempted or not. It is to help guest OS scheduling or lock checking
etc. Here add KVM_FEATURE_PREEMPT_HINT feature and use one byte as
preempted flag in steal time structure.
Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
---
arch/loongarch/include/asm/kvm_host.h | 2 +
arch/loongarch/include/asm/kvm_para.h | 5 +-
arch/loongarch/include/uapi/asm/kvm.h | 1 +
arch/loongarch/include/uapi/asm/kvm_para.h | 1 +
arch/loongarch/kvm/vcpu.c | 54 +++++++++++++++++++++-
arch/loongarch/kvm/vm.c | 5 +-
6 files changed, 65 insertions(+), 3 deletions(-)
diff --git a/arch/loongarch/include/asm/kvm_host.h b/arch/loongarch/include/asm/kvm_host.h
index 0cecbd038bb3..04c6dd171877 100644
--- a/arch/loongarch/include/asm/kvm_host.h
+++ b/arch/loongarch/include/asm/kvm_host.h
@@ -163,6 +163,7 @@ enum emulation_result {
#define LOONGARCH_PV_FEAT_UPDATED BIT_ULL(63)
#define LOONGARCH_PV_FEAT_MASK (BIT(KVM_FEATURE_IPI) | \
BIT(KVM_FEATURE_STEAL_TIME) | \
+ BIT(KVM_FEATURE_PREEMPT_HINT) |\
BIT(KVM_FEATURE_USER_HCALL) | \
BIT(KVM_FEATURE_VIRT_EXTIOI))
@@ -250,6 +251,7 @@ struct kvm_vcpu_arch {
u64 guest_addr;
u64 last_steal;
struct gfn_to_hva_cache cache;
+ u8 preempted;
} st;
};
diff --git a/arch/loongarch/include/asm/kvm_para.h b/arch/loongarch/include/asm/kvm_para.h
index 3e4b397f423f..d8592a7f5922 100644
--- a/arch/loongarch/include/asm/kvm_para.h
+++ b/arch/loongarch/include/asm/kvm_para.h
@@ -37,8 +37,11 @@ struct kvm_steal_time {
__u64 steal;
__u32 version;
__u32 flags;
- __u32 pad[12];
+ __u8 preempted;
+ __u8 u8_pad[3];
+ __u32 pad[11];
};
+#define KVM_VCPU_PREEMPTED (1 << 0)
/*
* Hypercall interface for KVM hypervisor
diff --git a/arch/loongarch/include/uapi/asm/kvm.h b/arch/loongarch/include/uapi/asm/kvm.h
index 57ba1a563bb1..bca7154aa651 100644
--- a/arch/loongarch/include/uapi/asm/kvm.h
+++ b/arch/loongarch/include/uapi/asm/kvm.h
@@ -104,6 +104,7 @@ struct kvm_fpu {
#define KVM_LOONGARCH_VM_FEAT_PV_IPI 6
#define KVM_LOONGARCH_VM_FEAT_PV_STEALTIME 7
#define KVM_LOONGARCH_VM_FEAT_PTW 8
+#define KVM_LOONGARCH_VM_FEAT_PV_PREEMPT_HINT 10
/* Device Control API on vcpu fd */
#define KVM_LOONGARCH_VCPU_CPUCFG 0
diff --git a/arch/loongarch/include/uapi/asm/kvm_para.h b/arch/loongarch/include/uapi/asm/kvm_para.h
index 76d802ef01ce..fe4107869ce6 100644
--- a/arch/loongarch/include/uapi/asm/kvm_para.h
+++ b/arch/loongarch/include/uapi/asm/kvm_para.h
@@ -15,6 +15,7 @@
#define CPUCFG_KVM_FEATURE (CPUCFG_KVM_BASE + 4)
#define KVM_FEATURE_IPI 1
#define KVM_FEATURE_STEAL_TIME 2
+#define KVM_FEATURE_PREEMPT_HINT 3
/* BIT 24 - 31 are features configurable by user space vmm */
#define KVM_FEATURE_VIRT_EXTIOI 24
#define KVM_FEATURE_USER_HCALL 25
diff --git a/arch/loongarch/kvm/vcpu.c b/arch/loongarch/kvm/vcpu.c
index 1245a6b35896..33a94b191b5d 100644
--- a/arch/loongarch/kvm/vcpu.c
+++ b/arch/loongarch/kvm/vcpu.c
@@ -180,6 +180,11 @@ static void kvm_update_stolen_time(struct kvm_vcpu *vcpu)
}
st = (struct kvm_steal_time __user *)ghc->hva;
+ if (kvm_guest_has_pv_feature(vcpu, KVM_FEATURE_PREEMPT_HINT)) {
+ unsafe_put_user(0, &st->preempted, out);
+ vcpu->arch.st.preempted = 0;
+ }
+
unsafe_get_user(version, &st->version, out);
if (version & 1)
version += 1; /* first time write, random junk */
@@ -1757,11 +1762,58 @@ static int _kvm_vcpu_put(struct kvm_vcpu *vcpu, int cpu)
return 0;
}
+static void _kvm_set_vcpu_preempted(struct kvm_vcpu *vcpu)
+{
+ struct gfn_to_hva_cache *ghc;
+ struct kvm_steal_time __user *st;
+ struct kvm_memslots *slots;
+ static const u8 preempted = KVM_VCPU_PREEMPTED;
+ gpa_t gpa;
+
+ gpa = vcpu->arch.st.guest_addr;
+ if (!(gpa & KVM_STEAL_PHYS_VALID))
+ return;
+
+ /* vCPU may be preempted for many times */
+ if (vcpu->arch.st.preempted)
+ return;
+
+ /* This happens on process exit */
+ if (unlikely(current->mm != vcpu->kvm->mm))
+ return;
+
+ gpa &= KVM_STEAL_PHYS_MASK;
+ ghc = &vcpu->arch.st.cache;
+ slots = kvm_memslots(vcpu->kvm);
+ if (slots->generation != ghc->generation || gpa != ghc->gpa) {
+ if (kvm_gfn_to_hva_cache_init(vcpu->kvm, ghc, gpa, sizeof(*st))) {
+ ghc->gpa = INVALID_GPA;
+ return;
+ }
+ }
+
+ st = (struct kvm_steal_time __user *)ghc->hva;
+ unsafe_put_user(preempted, &st->preempted, out);
+ vcpu->arch.st.preempted = KVM_VCPU_PREEMPTED;
+out:
+ mark_page_dirty_in_slot(vcpu->kvm, ghc->memslot, gpa_to_gfn(ghc->gpa));
+}
+
void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
{
- int cpu;
+ int cpu, idx;
unsigned long flags;
+ if (vcpu->preempted && kvm_guest_has_pv_feature(vcpu, KVM_FEATURE_PREEMPT_HINT)) {
+ /*
+ * Take the srcu lock as memslots will be accessed to check the gfn
+ * cache generation against the memslots generation.
+ */
+ idx = srcu_read_lock(&vcpu->kvm->srcu);
+ _kvm_set_vcpu_preempted(vcpu);
+ srcu_read_unlock(&vcpu->kvm->srcu, idx);
+ }
+
local_irq_save(flags);
cpu = smp_processor_id();
vcpu->arch.last_sched_cpu = cpu;
diff --git a/arch/loongarch/kvm/vm.c b/arch/loongarch/kvm/vm.c
index a49b1c1a3dd1..b8879110a0a1 100644
--- a/arch/loongarch/kvm/vm.c
+++ b/arch/loongarch/kvm/vm.c
@@ -45,8 +45,10 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
/* Enable all PV features by default */
kvm->arch.pv_features = BIT(KVM_FEATURE_IPI);
- if (kvm_pvtime_supported())
+ if (kvm_pvtime_supported()) {
kvm->arch.pv_features |= BIT(KVM_FEATURE_STEAL_TIME);
+ kvm->arch.pv_features |= BIT(KVM_FEATURE_PREEMPT_HINT);
+ }
/*
* cpu_vabits means user address space only (a half of total).
@@ -143,6 +145,7 @@ static int kvm_vm_feature_has_attr(struct kvm *kvm, struct kvm_device_attr *attr
case KVM_LOONGARCH_VM_FEAT_PV_IPI:
return 0;
case KVM_LOONGARCH_VM_FEAT_PV_STEALTIME:
+ case KVM_LOONGARCH_VM_FEAT_PV_PREEMPT_HINT:
if (kvm_pvtime_supported())
return 0;
return -ENXIO;
--
2.39.3
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