| 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: <03d39cc0-ed99-b32b-8678-575c646b6428@loongson.cn>
Date: Tue, 3 Feb 2026 15:48:25 +0800
From: Bibo Mao <maobibo@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>
Cc: WANG Xuerui <kernel@...0n.name>, Tianrui Zhao <zhaotianrui@...ngson.cn>,
loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v3 4/4] LoongArch: KVM: Add FPU delay load support
On 2026/2/3 下午3:34, Huacai Chen wrote:
> On Tue, Feb 3, 2026 at 2:48 PM Bibo Mao <maobibo@...ngson.cn> wrote:
>>
>>
>>
>> On 2026/2/3 下午12:15, Huacai Chen wrote:
>>> Hi, Bibo,
>>>
>>> On Tue, Feb 3, 2026 at 11:31 AM Bibo Mao <maobibo@...ngson.cn> wrote:
>>>>
>>>> FPU is lazy enabled with KVM hypervisor. After FPU is enabled and
>>>> loaded, vCPU can be preempted and FPU will be lost again, there will
>>>> be unnecessary FPU exception, load and store process. Here FPU is
>>>> delay load until guest enter entry.
>>> Calling LSX/LASX as FPU is a little strange, but somewhat reasonable.
>>> Calling LBT as FPU is very strange. So I still like the V1 logic.
>> yeap, LBT can use another different BIT and separate with FPU. It is
>> actually normal use one bit + fpu type variant to represent different
>> different FPU load requirement, such as
>> TIF_FOREIGN_FPSTATE/TIF_NEED_FPU_LOAD on other architectures.
>>
>> I think it is better to put int fpu_load_type in structure loongarch_fpu.
>>
>> And there will be another optimization to avoid load FPU again if FPU HW
>> is owned by current thread/vCPU, that will add last_cpu int type in
>> structure loongarch_fpu also.
>>
>> Regards
>> Bibo Mao
>>>
>>> If you insist on this version, please rename KVM_REQ_FPU_LOAD to
>>> KVM_REQ_AUX_LOAD and rename fpu_load_type to aux_type, which is
>>> similar to aux_inuse.
> Then why not consider this?
this can work now. However there is two different structure struct
loongarch_fpu and struct loongarch_lbt.
1. If kernel wants to use late FPU load, new element fpu_load_type can
be added in struct loongarch_fpu for both user app/KVM.
2. With further optimization, FPU HW can own by user app/kernel/KVM,
there will be another last_cpu int type added in struct loongarch_fpu.
Regards
Bibo Mao
Regards
Bibo Mao
>
> Huacai
>
>>>
>>> Huacai
>>>
>>>>
>>>> Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
>>>> ---
>>>> arch/loongarch/include/asm/kvm_host.h | 2 ++
>>>> arch/loongarch/kvm/exit.c | 21 ++++++++++-----
>>>> arch/loongarch/kvm/vcpu.c | 37 ++++++++++++++++++---------
>>>> 3 files changed, 41 insertions(+), 19 deletions(-)
>>>>
>>>> diff --git a/arch/loongarch/include/asm/kvm_host.h b/arch/loongarch/include/asm/kvm_host.h
>>>> index e4fe5b8e8149..902ff7bc0e35 100644
>>>> --- a/arch/loongarch/include/asm/kvm_host.h
>>>> +++ b/arch/loongarch/include/asm/kvm_host.h
>>>> @@ -37,6 +37,7 @@
>>>> #define KVM_REQ_TLB_FLUSH_GPA KVM_ARCH_REQ(0)
>>>> #define KVM_REQ_STEAL_UPDATE KVM_ARCH_REQ(1)
>>>> #define KVM_REQ_PMU KVM_ARCH_REQ(2)
>>>> +#define KVM_REQ_FPU_LOAD KVM_ARCH_REQ(3)
>>>>
>>>> #define KVM_GUESTDBG_SW_BP_MASK \
>>>> (KVM_GUESTDBG_ENABLE | KVM_GUESTDBG_USE_SW_BP)
>>>> @@ -234,6 +235,7 @@ struct kvm_vcpu_arch {
>>>> u64 vpid;
>>>> gpa_t flush_gpa;
>>>>
>>>> + int fpu_load_type;
>>>> /* Frequency of stable timer in Hz */
>>>> u64 timer_mhz;
>>>> ktime_t expire;
>>>> diff --git a/arch/loongarch/kvm/exit.c b/arch/loongarch/kvm/exit.c
>>>> index 65ec10a7245a..62403c7c6f9a 100644
>>>> --- a/arch/loongarch/kvm/exit.c
>>>> +++ b/arch/loongarch/kvm/exit.c
>>>> @@ -754,7 +754,8 @@ static int kvm_handle_fpu_disabled(struct kvm_vcpu *vcpu, int ecode)
>>>> return RESUME_HOST;
>>>> }
>>>>
>>>> - kvm_own_fpu(vcpu);
>>>> + vcpu->arch.fpu_load_type = KVM_LARCH_FPU;
>>>> + kvm_make_request(KVM_REQ_FPU_LOAD, vcpu);
>>>>
>>>> return RESUME_GUEST;
>>>> }
>>>> @@ -794,8 +795,10 @@ static int kvm_handle_lsx_disabled(struct kvm_vcpu *vcpu, int ecode)
>>>> {
>>>> if (!kvm_guest_has_lsx(&vcpu->arch))
>>>> kvm_queue_exception(vcpu, EXCCODE_INE, 0);
>>>> - else
>>>> - kvm_own_lsx(vcpu);
>>>> + else {
>>>> + vcpu->arch.fpu_load_type = KVM_LARCH_LSX;
>>>> + kvm_make_request(KVM_REQ_FPU_LOAD, vcpu);
>>>> + }
>>>>
>>>> return RESUME_GUEST;
>>>> }
>>>> @@ -812,8 +815,10 @@ static int kvm_handle_lasx_disabled(struct kvm_vcpu *vcpu, int ecode)
>>>> {
>>>> if (!kvm_guest_has_lasx(&vcpu->arch))
>>>> kvm_queue_exception(vcpu, EXCCODE_INE, 0);
>>>> - else
>>>> - kvm_own_lasx(vcpu);
>>>> + else {
>>>> + vcpu->arch.fpu_load_type = KVM_LARCH_LASX;
>>>> + kvm_make_request(KVM_REQ_FPU_LOAD, vcpu);
>>>> + }
>>>>
>>>> return RESUME_GUEST;
>>>> }
>>>> @@ -822,8 +827,10 @@ static int kvm_handle_lbt_disabled(struct kvm_vcpu *vcpu, int ecode)
>>>> {
>>>> if (!kvm_guest_has_lbt(&vcpu->arch))
>>>> kvm_queue_exception(vcpu, EXCCODE_INE, 0);
>>>> - else
>>>> - kvm_own_lbt(vcpu);
>>>> + else {
>>>> + vcpu->arch.fpu_load_type = KVM_LARCH_LBT;
>>>> + kvm_make_request(KVM_REQ_FPU_LOAD, vcpu);
>>>> + }
>>>>
>>>> return RESUME_GUEST;
>>>> }
>>>> diff --git a/arch/loongarch/kvm/vcpu.c b/arch/loongarch/kvm/vcpu.c
>>>> index 995461d724b5..d05fe6c8f456 100644
>>>> --- a/arch/loongarch/kvm/vcpu.c
>>>> +++ b/arch/loongarch/kvm/vcpu.c
>>>> @@ -232,6 +232,31 @@ static void kvm_late_check_requests(struct kvm_vcpu *vcpu)
>>>> kvm_flush_tlb_gpa(vcpu, vcpu->arch.flush_gpa);
>>>> vcpu->arch.flush_gpa = INVALID_GPA;
>>>> }
>>>> +
>>>> + if (kvm_check_request(KVM_REQ_FPU_LOAD, vcpu)) {
>>>> + switch (vcpu->arch.fpu_load_type) {
>>>> + case KVM_LARCH_FPU:
>>>> + kvm_own_fpu(vcpu);
>>>> + break;
>>>> +
>>>> + case KVM_LARCH_LSX:
>>>> + kvm_own_lsx(vcpu);
>>>> + break;
>>>> +
>>>> + case KVM_LARCH_LASX:
>>>> + kvm_own_lasx(vcpu);
>>>> + break;
>>>> +
>>>> + case KVM_LARCH_LBT:
>>>> + kvm_own_lbt(vcpu);
>>>> + break;
>>>> +
>>>> + default:
>>>> + break;
>>>> + }
>>>> +
>>>> + vcpu->arch.fpu_load_type = 0;
>>>> + }
>>>> }
>>>>
>>>> /*
>>>> @@ -1286,13 +1311,11 @@ int kvm_arch_vcpu_ioctl_set_fpu(struct kvm_vcpu *vcpu, struct kvm_fpu *fpu)
>>>> #ifdef CONFIG_CPU_HAS_LBT
>>>> int kvm_own_lbt(struct kvm_vcpu *vcpu)
>>>> {
>>>> - preempt_disable();
>>>> if (!(vcpu->arch.aux_inuse & KVM_LARCH_LBT)) {
>>>> set_csr_euen(CSR_EUEN_LBTEN);
>>>> _restore_lbt(&vcpu->arch.lbt);
>>>> vcpu->arch.aux_inuse |= KVM_LARCH_LBT;
>>>> }
>>>> - preempt_enable();
>>>>
>>>> return 0;
>>>> }
>>>> @@ -1335,8 +1358,6 @@ static inline void kvm_check_fcsr_alive(struct kvm_vcpu *vcpu) { }
>>>> /* Enable FPU and restore context */
>>>> void kvm_own_fpu(struct kvm_vcpu *vcpu)
>>>> {
>>>> - preempt_disable();
>>>> -
>>>> /*
>>>> * Enable FPU for guest
>>>> * Set FR and FRE according to guest context
>>>> @@ -1347,16 +1368,12 @@ void kvm_own_fpu(struct kvm_vcpu *vcpu)
>>>> kvm_restore_fpu(&vcpu->arch.fpu);
>>>> vcpu->arch.aux_inuse |= KVM_LARCH_FPU;
>>>> trace_kvm_aux(vcpu, KVM_TRACE_AUX_RESTORE, KVM_TRACE_AUX_FPU);
>>>> -
>>>> - preempt_enable();
>>>> }
>>>>
>>>> #ifdef CONFIG_CPU_HAS_LSX
>>>> /* Enable LSX and restore context */
>>>> int kvm_own_lsx(struct kvm_vcpu *vcpu)
>>>> {
>>>> - preempt_disable();
>>>> -
>>>> /* Enable LSX for guest */
>>>> kvm_check_fcsr(vcpu, vcpu->arch.fpu.fcsr);
>>>> set_csr_euen(CSR_EUEN_LSXEN | CSR_EUEN_FPEN);
>>>> @@ -1378,7 +1395,6 @@ int kvm_own_lsx(struct kvm_vcpu *vcpu)
>>>>
>>>> trace_kvm_aux(vcpu, KVM_TRACE_AUX_RESTORE, KVM_TRACE_AUX_LSX);
>>>> vcpu->arch.aux_inuse |= KVM_LARCH_LSX | KVM_LARCH_FPU;
>>>> - preempt_enable();
>>>>
>>>> return 0;
>>>> }
>>>> @@ -1388,8 +1404,6 @@ int kvm_own_lsx(struct kvm_vcpu *vcpu)
>>>> /* Enable LASX and restore context */
>>>> int kvm_own_lasx(struct kvm_vcpu *vcpu)
>>>> {
>>>> - preempt_disable();
>>>> -
>>>> kvm_check_fcsr(vcpu, vcpu->arch.fpu.fcsr);
>>>> set_csr_euen(CSR_EUEN_FPEN | CSR_EUEN_LSXEN | CSR_EUEN_LASXEN);
>>>> switch (vcpu->arch.aux_inuse & (KVM_LARCH_FPU | KVM_LARCH_LSX)) {
>>>> @@ -1411,7 +1425,6 @@ int kvm_own_lasx(struct kvm_vcpu *vcpu)
>>>>
>>>> trace_kvm_aux(vcpu, KVM_TRACE_AUX_RESTORE, KVM_TRACE_AUX_LASX);
>>>> vcpu->arch.aux_inuse |= KVM_LARCH_LASX | KVM_LARCH_LSX | KVM_LARCH_FPU;
>>>> - preempt_enable();
>>>>
>>>> return 0;
>>>> }
>>>> --
>>>> 2.39.3
>>>>
>>>>
>>
>>
Powered by blists - more mailing lists