Re: [PATCH] LoongArch: KVM: Add hypercall crash support
From: Huacai Chen
Date: Sat Oct 03 2026 - 00:08:13 EST
Hi, Bibo,
On Wed, Sep 9, 2026 at 5:01 PM Bibo Mao <maobibo@xxxxxxxxxxx> wrote:
>
> Now generic pvpanic is supported in Linux kernel which will notify VMM
> with VM crash event. There is some limitations with pvpanic, such as it
> requires good kernel stack or CPU hardware context and panic() C function
> is in health state.
>
> Sometimes CPU hardware context or kernel/irq stack is corrupted. Hypercall
> code is more direct and low-level crash method, which is useful in
> exception entry with assmble language, here add one hypercall code to
> support VM crash function, so that VMM can capture CPU crash context
> in time.
>
> Signed-off-by: Bibo Mao <maobibo@xxxxxxxxxxx>
> ---
> arch/loongarch/include/asm/kvm_host.h | 1 +
> arch/loongarch/include/asm/kvm_para.h | 15 +++++++++++++++
> arch/loongarch/include/uapi/asm/kvm.h | 1 +
> arch/loongarch/include/uapi/asm/kvm_para.h | 1 +
> arch/loongarch/kvm/exit.c | 11 +++++++++++
> arch/loongarch/kvm/vm.c | 3 ++-
> 6 files changed, 31 insertions(+), 1 deletion(-)
>
> diff --git a/arch/loongarch/include/asm/kvm_host.h b/arch/loongarch/include/asm/kvm_host.h
> index 65d91c3ce313..96f9f1317cad 100644
> --- a/arch/loongarch/include/asm/kvm_host.h
> +++ b/arch/loongarch/include/asm/kvm_host.h
> @@ -168,6 +168,7 @@ enum emulation_result {
> #define LOONGARCH_PV_FEAT_MASK (BIT(KVM_FEATURE_IPI) | \
> BIT(KVM_FEATURE_PREEMPT) | \
> BIT(KVM_FEATURE_STEAL_TIME) | \
> + BIT(KVM_FEATURE_CRASH) | \
> BIT(KVM_FEATURE_USER_HCALL) | \
> BIT(KVM_FEATURE_VIRT_EXTIOI))
>
> diff --git a/arch/loongarch/include/asm/kvm_para.h b/arch/loongarch/include/asm/kvm_para.h
> index fb17ba0fa101..3b183bb1aaa8 100644
> --- a/arch/loongarch/include/asm/kvm_para.h
> +++ b/arch/loongarch/include/asm/kvm_para.h
> @@ -14,6 +14,7 @@
> #define KVM_HCALL_CODE_SERVICE 0
> #define KVM_HCALL_CODE_SWDBG 1
> #define KVM_HCALL_CODE_USER_SERVICE 2
> +#define KVM_HCALL_CODE_CRASH 3
>
> #define KVM_HCALL_SERVICE HYPERCALL_ENCODE(HYPERVISOR_KVM, KVM_HCALL_CODE_SERVICE)
> #define KVM_HCALL_FUNC_IPI 1
> @@ -22,6 +23,7 @@
> #define KVM_HCALL_SWDBG HYPERCALL_ENCODE(HYPERVISOR_KVM, KVM_HCALL_CODE_SWDBG)
>
> #define KVM_HCALL_USER_SERVICE HYPERCALL_ENCODE(HYPERVISOR_KVM, KVM_HCALL_CODE_USER_SERVICE)
> +#define KVM_HCALL_CRASH HYPERCALL_ENCODE(HYPERVISOR_KVM, KVM_HCALL_CODE_CRASH)
>
> /*
> * LoongArch hypercall return code
> @@ -161,6 +163,19 @@ static __always_inline long kvm_hypercall5(u64 fid,
> return ret;
> }
>
> +static __always_inline long kvm_hypercall_crash(void)
> +{
> + register long ret asm("a0");
> +
> + __asm__ __volatile__(
> + "hvcl "__stringify(KVM_HCALL_CRASH)
> + : "=r" (ret)
> + : : "memory"
> + );
> +
> + return ret;
> +}
Why this function has no caller?
Huacai
> +
> #ifdef CONFIG_PARAVIRT
> bool kvm_para_available(void);
> unsigned int kvm_arch_para_features(void);
> diff --git a/arch/loongarch/include/uapi/asm/kvm.h b/arch/loongarch/include/uapi/asm/kvm.h
> index cd0b5c11ca9c..b222bfc48042 100644
> --- a/arch/loongarch/include/uapi/asm/kvm.h
> +++ b/arch/loongarch/include/uapi/asm/kvm.h
> @@ -106,6 +106,7 @@ struct kvm_fpu {
> #define KVM_LOONGARCH_VM_FEAT_PTW 8
> #define KVM_LOONGARCH_VM_FEAT_MSGINT 9
> #define KVM_LOONGARCH_VM_FEAT_PV_PREEMPT 10
> +#define KVM_LOONGARCH_VM_FEAT_CRASH 11
>
> /* 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 d28cbcadd276..bf1a0c826ca6 100644
> --- a/arch/loongarch/include/uapi/asm/kvm_para.h
> +++ b/arch/loongarch/include/uapi/asm/kvm_para.h
> @@ -16,6 +16,7 @@
> #define KVM_FEATURE_IPI 1
> #define KVM_FEATURE_STEAL_TIME 2
> #define KVM_FEATURE_PREEMPT 3
> +#define KVM_FEATURE_CRASH 4
> /* 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/exit.c b/arch/loongarch/kvm/exit.c
> index 4f58e6e2cf86..3b6daa946c76 100644
> --- a/arch/loongarch/kvm/exit.c
> +++ b/arch/loongarch/kvm/exit.c
> @@ -911,6 +911,17 @@ static int kvm_handle_hypercall(struct kvm_vcpu *vcpu, int ecode)
> vcpu->run->hypercall.ret = KVM_HCALL_INVALID_CODE;
> ret = RESUME_HOST;
> break;
> + case KVM_HCALL_CRASH:
> + if (!kvm_guest_has_pv_feature(vcpu, KVM_FEATURE_CRASH)) {
> + kvm_write_reg(vcpu, LOONGARCH_GPR_A0, KVM_HCALL_INVALID_CODE);
> + break;
> + }
> +
> + vcpu->run->exit_reason = KVM_EXIT_SYSTEM_EVENT;
> + vcpu->run->system_event.type = KVM_SYSTEM_EVENT_CRASH;
> + vcpu->run->system_event.ndata = 0;
> + ret = RESUME_HOST;
> + break;
> case KVM_HCALL_SWDBG:
> /* KVM_HCALL_SWDBG only in effective when SW_BP is enabled */
> if (vcpu->guest_debug & KVM_GUESTDBG_SW_BP_MASK) {
> diff --git a/arch/loongarch/kvm/vm.c b/arch/loongarch/kvm/vm.c
> index 6dabb227a732..e5d10ceb5e67 100644
> --- a/arch/loongarch/kvm/vm.c
> +++ b/arch/loongarch/kvm/vm.c
> @@ -49,8 +49,9 @@ static void kvm_vm_init_features(struct kvm *kvm)
> kvm->arch.kvm_features |= BIT(KVM_LOONGARCH_VM_FEAT_PMU);
>
> /* Enable all PV features by default */
> - kvm->arch.pv_features |= BIT(KVM_FEATURE_IPI);
> + kvm->arch.pv_features |= BIT(KVM_FEATURE_IPI) | BIT(KVM_FEATURE_CRASH);
> kvm->arch.kvm_features |= BIT(KVM_LOONGARCH_VM_FEAT_PV_IPI);
> + kvm->arch.kvm_features |= BIT(KVM_LOONGARCH_VM_FEAT_CRASH);
> if (kvm_pvtime_supported()) {
> kvm->arch.pv_features |= BIT(KVM_FEATURE_PREEMPT);
> kvm->arch.pv_features |= BIT(KVM_FEATURE_STEAL_TIME);
>
> base-commit: df2908090cda368b01ff43709f51890076c56157
> --
> 2.39.3
>
>