| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <3e36f507-a907-7143-41a7-58dbefb73fb5@loongson.cn>
Date: Wed, 19 Nov 2025 09:20:46 +0800
From: Bibo Mao <maobibo@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>
Cc: Paolo Bonzini <pbonzini@...hat.com>,
Tianrui Zhao <zhaotianrui@...ngson.cn>, WANG Xuerui <kernel@...0n.name>,
kvm@...r.kernel.org, loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] LoongArch: KVM: Add preempt hint feature in
hypervisor side
On 2025/11/18 下午8:46, Huacai Chen wrote:
> Hi, Bibo,
>
> On Tue, Nov 18, 2025 at 4:07 PM Bibo Mao <maobibo@...ngson.cn> wrote:
>>
>> 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];
> Maybe a single __u8 pad[47] is enough?
yes, pad[47] seems better unless there is definitely __u32 type
requirement in future.
Will do in next version.
>
>> };
>> +#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
> From the name it is a "hint", from include/linux/kvm_para.h we know
> features and hints are different. If preempt is really a feature,
> rename it?
It is a feature. yes, in generic hint is suggestion for VM and VM can
selectively do or not.
Will rename it with KVM_LOONGARCH_VM_FEAT_PV_PREEMPT.
>
>>
>> /* 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)
> Just using kvm_set_vcpu_preempted() is enough, no "_".
>
>> +{
>> + struct gfn_to_hva_cache *ghc;
>> + struct kvm_steal_time __user *st;
>> + struct kvm_memslots *slots;
>> + static const u8 preempted = KVM_VCPU_PREEMPTED;
> I'm not sure whether "static" is right, it's not reentrant.
I think static is better here, it saves one cycle with assignment here.
Regards
Bibo Mao
>
>
> Huacai
>
>> + 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
>>
>>
Powered by blists - more mailing lists