* [PATCH v2] LoongArch: KVM: Add hypercall crash support
@ 2026-10-16 3:42 Bibo Mao
2026-10-16 3:57 ` sashiko-bot
2026-10-16 4:32 ` Huacai Chen
0 siblings, 2 replies; 5+ messages in thread
From: Bibo Mao @ 2026-10-16 3:42 UTC (permalink / raw)
To: Huacai Chen; +Cc: WANG Xuerui, kvm, loongarch, linux-kernel
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@loongson.cn>
---
v1 ... v2:
1. Add VM feature checking with KVM_LOONGARCH_VM_FEAT_CRASH from VMM
user space.
---
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 | 4 +++-
6 files changed, 32 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;
+}
+
#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..9bf4b3bb8f25 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);
@@ -163,6 +164,7 @@ static int kvm_vm_feature_has_attr(struct kvm *kvm, struct kvm_device_attr *attr
case KVM_LOONGARCH_VM_FEAT_PV_IPI:
case KVM_LOONGARCH_VM_FEAT_PV_PREEMPT:
case KVM_LOONGARCH_VM_FEAT_PV_STEALTIME:
+ case KVM_LOONGARCH_VM_FEAT_CRASH:
if (kvm_vm_support(&kvm->arch, attr->attr))
return 0;
return -ENXIO;
base-commit: 2f2f7eeef8b0a1a9b9ca998231419873ccae8d4e
--
2.39.3
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH v2] LoongArch: KVM: Add hypercall crash support
2026-10-16 3:42 [PATCH v2] LoongArch: KVM: Add hypercall crash support Bibo Mao
@ 2026-10-16 3:57 ` sashiko-bot
2026-10-16 4:15 ` Bibo Mao
2026-10-16 4:32 ` Huacai Chen
1 sibling, 1 reply; 5+ messages in thread
From: sashiko-bot @ 2026-10-16 3:57 UTC (permalink / raw)
To: Bibo Mao; +Cc: kvm
Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] kvm: new guest-visible KVM_FEATURE_CRASH capability is silently enabled by default
--
commit 6d0e897e0c46a79eb02651baa4b7271884b07abb
Author: Bibo Mao <maobibo@loongson.cn>
LoongArch: KVM: Add hypercall crash support
This commit adds hypercall crash support (KVM_HCALL_CRASH) to LoongArch KVM
to provide a more direct, low-level crash notification method. It allows the
VMM to capture CPU crash context during exception entry even if the CPU
hardware context or kernel stack is corrupted.
> diff --git a/arch/loongarch/kvm/vm.c b/arch/loongarch/kvm/vm.c
> index 6dabb227a7321..9bf4b3bb8f25a 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);
[Severity: High]
Does unconditionally setting BIT(KVM_FEATURE_CRASH) and
BIT(KVM_LOONGARCH_VM_FEAT_CRASH) here break live migration and backward
compatibility?
If a VM is migrated to a newer kernel with this patch, an older VMM unaware
of the capability will not explicitly disable it. If the guest discovers
and triggers the new KVM_HCALL_CRASH hypercall, the older VMM will receive
an unexpected KVM_EXIT_SYSTEM_EVENT and will likely terminate the VM.
Should new guest-visible capabilities be left off by default and require
explicit VMM opt-in through capability negotiation?
--
Sashiko AI review · https://sashiko.dev/#/patchset/20261016034245.3002859-1-maobibo@loongson.cn?part=1
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v2] LoongArch: KVM: Add hypercall crash support
2026-10-16 3:57 ` sashiko-bot
@ 2026-10-16 4:15 ` Bibo Mao
0 siblings, 0 replies; 5+ messages in thread
From: Bibo Mao @ 2026-10-16 4:15 UTC (permalink / raw)
To: sashiko-reviews; +Cc: kvm
On 2026/10/16 上午11:57, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] kvm: new guest-visible KVM_FEATURE_CRASH capability is silently enabled by default
> --
>
> commit 6d0e897e0c46a79eb02651baa4b7271884b07abb
> Author: Bibo Mao <maobibo@loongson.cn>
> LoongArch: KVM: Add hypercall crash support
>
> This commit adds hypercall crash support (KVM_HCALL_CRASH) to LoongArch KVM
> to provide a more direct, low-level crash notification method. It allows the
> VMM to capture CPU crash context during exception entry even if the CPU
> hardware context or kernel stack is corrupted.
>
>> diff --git a/arch/loongarch/kvm/vm.c b/arch/loongarch/kvm/vm.c
>> index 6dabb227a7321..9bf4b3bb8f25a 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);
>
> [Severity: High]
> Does unconditionally setting BIT(KVM_FEATURE_CRASH) and
> BIT(KVM_LOONGARCH_VM_FEAT_CRASH) here break live migration and backward
> compatibility?
>
> If a VM is migrated to a newer kernel with this patch, an older VMM unaware
> of the capability will not explicitly disable it. If the guest discovers
> and triggers the new KVM_HCALL_CRASH hypercall, the older VMM will receive
> an unexpected KVM_EXIT_SYSTEM_EVENT and will likely terminate the VM.
>
> Should new guest-visible capabilities be left off by default and require
> explicit VMM opt-in through capability negotiation?
The design idea is that if VMM does not set pv features, kvm will enable
all supported features. With VM migration, VMM need set pv features
again in post migration stage, so it is the problem of VMM, rather than KVM.
Regards
Bibo Mao
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v2] LoongArch: KVM: Add hypercall crash support
2026-10-16 3:42 [PATCH v2] LoongArch: KVM: Add hypercall crash support Bibo Mao
2026-10-16 3:57 ` sashiko-bot
@ 2026-10-16 4:32 ` Huacai Chen
2026-10-16 6:24 ` Bibo Mao
1 sibling, 1 reply; 5+ messages in thread
From: Huacai Chen @ 2026-10-16 4:32 UTC (permalink / raw)
To: Bibo Mao; +Cc: WANG Xuerui, kvm, loongarch, linux-kernel
V1 in the pull-request has been merged.
Huacai
On Fri, Oct 16, 2026 at 11:43 AM Bibo Mao <maobibo@loongson.cn> 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@loongson.cn>
> ---
> v1 ... v2:
> 1. Add VM feature checking with KVM_LOONGARCH_VM_FEAT_CRASH from VMM
> user space.
> ---
> 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 | 4 +++-
> 6 files changed, 32 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;
> +}
> +
> #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..9bf4b3bb8f25 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);
> @@ -163,6 +164,7 @@ static int kvm_vm_feature_has_attr(struct kvm *kvm, struct kvm_device_attr *attr
> case KVM_LOONGARCH_VM_FEAT_PV_IPI:
> case KVM_LOONGARCH_VM_FEAT_PV_PREEMPT:
> case KVM_LOONGARCH_VM_FEAT_PV_STEALTIME:
> + case KVM_LOONGARCH_VM_FEAT_CRASH:
> if (kvm_vm_support(&kvm->arch, attr->attr))
> return 0;
> return -ENXIO;
>
> base-commit: 2f2f7eeef8b0a1a9b9ca998231419873ccae8d4e
> --
> 2.39.3
>
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v2] LoongArch: KVM: Add hypercall crash support
2026-10-16 4:32 ` Huacai Chen
@ 2026-10-16 6:24 ` Bibo Mao
0 siblings, 0 replies; 5+ messages in thread
From: Bibo Mao @ 2026-10-16 6:24 UTC (permalink / raw)
To: Huacai Chen; +Cc: WANG Xuerui, kvm, loongarch, linux-kernel
On 2026/10/16 下午12:32, Huacai Chen wrote:
> V1 in the pull-request has been merged.
It is my fault. Will submit the fix version after rc1.
Regards
Bibo Mao
>
> Huacai
>
> On Fri, Oct 16, 2026 at 11:43 AM Bibo Mao <maobibo@loongson.cn> 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@loongson.cn>
>> ---
>> v1 ... v2:
>> 1. Add VM feature checking with KVM_LOONGARCH_VM_FEAT_CRASH from VMM
>> user space.
>> ---
>> 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 | 4 +++-
>> 6 files changed, 32 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;
>> +}
>> +
>> #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..9bf4b3bb8f25 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);
>> @@ -163,6 +164,7 @@ static int kvm_vm_feature_has_attr(struct kvm *kvm, struct kvm_device_attr *attr
>> case KVM_LOONGARCH_VM_FEAT_PV_IPI:
>> case KVM_LOONGARCH_VM_FEAT_PV_PREEMPT:
>> case KVM_LOONGARCH_VM_FEAT_PV_STEALTIME:
>> + case KVM_LOONGARCH_VM_FEAT_CRASH:
>> if (kvm_vm_support(&kvm->arch, attr->attr))
>> return 0;
>> return -ENXIO;
>>
>> base-commit: 2f2f7eeef8b0a1a9b9ca998231419873ccae8d4e
>> --
>> 2.39.3
>>
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2026-10-16 6:23 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2026-10-16 3:42 [PATCH v2] LoongArch: KVM: Add hypercall crash support Bibo Mao
2026-10-16 3:57 ` sashiko-bot
2026-10-16 4:15 ` Bibo Mao
2026-10-16 4:32 ` Huacai Chen
2026-10-16 6:24 ` Bibo Mao
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