Re: [PATCH] LoongArch: KVM: Add hypercall crash support
From: Bibo Mao
Date: Thu Oct 15 2026 - 23:29:36 EST
On 2026/10/16 上午9:06, Bibo Mao wrote:
My bad. There is problem which is pointed out by sashiko-bot. I had thought I have sent v2 version already. Will send v2 soon.
On 2026/10/14 下午12:30, Huacai Chen wrote:
On Mon, Oct 12, 2026 at 8:55 AM Bibo Mao <maobibo@xxxxxxxxxxx> wrote:Thanks. there is no problem from the code side, will test this in 7.4- rc1 version.
Now all KVM patches for 7.4 is merged to loongarch-kvm. You can test
On 2026/10/11 下午10:06, Huacai Chen wrote:
On Thu, Oct 8, 2026 at 9:50 AM Bibo Mao <maobibo@xxxxxxxxxxx> wrote:Removinge the example usage with KVM_HCALL_CRASH is fine to me.
There are no examples for KVM_HCALL_SWDBG and KVM_HCALL_USER_SERVICE,
On 2026/10/3 下午12:02, Huacai Chen wrote:
Hi, Bibo,Currently we directly modify guest kernel and hard-code the hypercall
On Wed, Sep 9, 2026 at 5:01 PM Bibo Mao <maobibo@xxxxxxxxxxx> wrote:
Why this function has no caller?
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;
+}
instruction to debug. This inline function is only example for howto
usage, the normal usage such as checking KVM_FEATURE_USER_HCALL feature
+ kvm_hypercall_crash() is too complicated in exception entry assemble
language.
I think KVM_HCALL_CRASH is no special.
So if you agree, I will remove this example when applying.
it if you want.
diff --git a/arch/loongarch/kvm/vm.c b/arch/loongarch/kvm/vm.c
index e5d10ceb5e67..9bf4b3bb8f25 100644
--- a/arch/loongarch/kvm/vm.c
+++ b/arch/loongarch/kvm/vm.c
@@ -164,6 +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;
Regards
Bibo Mao
Regards
bibo
Huacai
Regards
Bibo Mao
Huacai
Regards
Bibo Mao
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