Re: [PATCH] LoongArch: KVM: Add hypercall service support for usermode VMM
From: bibo mao
Date: Tue Dec 31 2024 - 04:27:43 EST
On 2024/12/31 下午4:41, Huacai Chen wrote:
On Mon, Dec 30, 2024 at 10:13 AM bibo mao <maobibo@xxxxxxxxxxx> wrote:
Hi Huacai,
On 2024/12/23 下午5:05, Huacai Chen wrote:
I also tried to port an untested version, but I think your version is
a tested one.
https://github.com/chenhuacai/linux/commit/e6596b0e45c80756794aba74ac086c5c0e0306eb
And I have some questions:
1, "user service" is not only for syscall, so you rename it?
2, Why 4.19 doesn't need something like "vcpu->run->hypercall.args[0]
= kvm_read_reg(vcpu, LOONGARCH_GPR_A0);"
3, I think my version about "vcpu->run->exit_reason =
KVM_EXIT_HYPERCALL;" and "update_pc()" is a little better than yours,
so you can improve them.
After a second thought, update_pc() before return to user may be not
strictly right, since user VMM can dump registers including pc which is
advanced already.
Agree, and we can see how others do.
How about adding function kvm_complete_hypercall() like
kvm_complete_mmio_read(), such as:
kvm_complete_user_service() maybe better? Since the "classic
hypercall" doesn't come here.
sure, will do rename it with kvm_complete_user_service.
And we may also need to set vcpu->run->exit_reason for all cases,
which is done in my version.
By my understanding, exit_reason need be set only for RESUME_HOST.
it is unnecessary for RESUME_GUEST.
Regards
Bibo Mao
Huacai
--- a/arch/loongarch/kvm/exit.c
+++ b/arch/loongarch/kvm/exit.c
+int kvm_complete_hypercall(struct kvm_vcpu *vcpu, struct kvm_run *run)
+{
+ update_pc(&vcpu->arch);
+ kvm_write_reg(vcpu, LOONGARCH_GPR_A0, run->hypercall.ret);
+}
+
--- a/arch/loongarch/kvm/vcpu.c
+++ b/arch/loongarch/kvm/vcpu.c
@@ -1736,8 +1736,8 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
if (!run->iocsr_io.is_write)
kvm_complete_iocsr_read(vcpu, run);
} else if (run->exit_reason == KVM_EXIT_HYPERCALL) {
- kvm_write_reg(vcpu, LOONGARCH_GPR_A0, run->hypercall.ret);
- update_pc(&vcpu->arch);
+ kvm_complete_hypercall(vcpu, run);
+ run->exit_reason = KVM_EXIT_UNKNOWN;
}
Regards
Bibo Mao
Huacai
On Mon, Dec 23, 2024 at 4:54 PM bibo mao <maobibo@xxxxxxxxxxx> wrote:
On 2024/12/23 下午4:50, Huacai Chen wrote:
Hi, Bibo,
Is this patch trying to do the same thing as "LoongArch: add hypcall
to emulate syscall in kvm" in 4.19?
yes, it is to do so -:)
Regards
Bibo Mao
Huacai
On Mon, Dec 23, 2024 at 4:42 PM Bibo Mao <maobibo@xxxxxxxxxxx> wrote:
Some VMMs provides special hypercall service in usermode, KVM need
not handle the usermode hypercall service and pass it to VMM and
let VMM handle it.
Here new code KVM_HCALL_CODE_USER is added for user-mode hypercall
service, KVM loads all six registers to VMM.
Signed-off-by: Bibo Mao <maobibo@xxxxxxxxxxx>
---
arch/loongarch/include/asm/kvm_host.h | 1 +
arch/loongarch/include/asm/kvm_para.h | 2 ++
arch/loongarch/include/uapi/asm/kvm_para.h | 1 +
arch/loongarch/kvm/exit.c | 22 ++++++++++++++++++++++
arch/loongarch/kvm/vcpu.c | 3 +++
5 files changed, 29 insertions(+)
diff --git a/arch/loongarch/include/asm/kvm_host.h b/arch/loongarch/include/asm/kvm_host.h
index 7b8367c39da8..590982cd986e 100644
--- a/arch/loongarch/include/asm/kvm_host.h
+++ b/arch/loongarch/include/asm/kvm_host.h
@@ -162,6 +162,7 @@ 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_USER_HCALL) | \
BIT(KVM_FEATURE_VIRT_EXTIOI))
struct kvm_vcpu_arch {
diff --git a/arch/loongarch/include/asm/kvm_para.h b/arch/loongarch/include/asm/kvm_para.h
index c4e84227280d..d3c00de484f6 100644
--- a/arch/loongarch/include/asm/kvm_para.h
+++ b/arch/loongarch/include/asm/kvm_para.h
@@ -13,12 +13,14 @@
#define KVM_HCALL_CODE_SERVICE 0
#define KVM_HCALL_CODE_SWDBG 1
+#define KVM_HCALL_CODE_USER 2
#define KVM_HCALL_SERVICE HYPERCALL_ENCODE(HYPERVISOR_KVM, KVM_HCALL_CODE_SERVICE)
#define KVM_HCALL_FUNC_IPI 1
#define KVM_HCALL_FUNC_NOTIFY 2
#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)
/*
* LoongArch hypercall return code
diff --git a/arch/loongarch/include/uapi/asm/kvm_para.h b/arch/loongarch/include/uapi/asm/kvm_para.h
index b0604aa9b4bb..76d802ef01ce 100644
--- a/arch/loongarch/include/uapi/asm/kvm_para.h
+++ b/arch/loongarch/include/uapi/asm/kvm_para.h
@@ -17,5 +17,6 @@
#define KVM_FEATURE_STEAL_TIME 2
/* BIT 24 - 31 are features configurable by user space vmm */
#define KVM_FEATURE_VIRT_EXTIOI 24
+#define KVM_FEATURE_USER_HCALL 25
#endif /* _UAPI_ASM_KVM_PARA_H */
diff --git a/arch/loongarch/kvm/exit.c b/arch/loongarch/kvm/exit.c
index a7893bd01e73..1a85cd4fb6a5 100644
--- a/arch/loongarch/kvm/exit.c
+++ b/arch/loongarch/kvm/exit.c
@@ -873,6 +873,28 @@ static int kvm_handle_hypercall(struct kvm_vcpu *vcpu)
vcpu->stat.hypercall_exits++;
kvm_handle_service(vcpu);
break;
+ case KVM_HCALL_USER_SERVICE:
+ if (!kvm_guest_has_pv_feature(vcpu, KVM_FEATURE_USER_HCALL)) {
+ kvm_write_reg(vcpu, LOONGARCH_GPR_A0, KVM_HCALL_INVALID_CODE);
+ break;
+ }
+
+ vcpu->run->exit_reason = KVM_EXIT_HYPERCALL;
+ vcpu->run->hypercall.nr = KVM_HCALL_USER_SERVICE;
+ vcpu->run->hypercall.args[0] = kvm_read_reg(vcpu, LOONGARCH_GPR_A0);
+ vcpu->run->hypercall.args[1] = kvm_read_reg(vcpu, LOONGARCH_GPR_A1);
+ vcpu->run->hypercall.args[2] = kvm_read_reg(vcpu, LOONGARCH_GPR_A2);
+ vcpu->run->hypercall.args[3] = kvm_read_reg(vcpu, LOONGARCH_GPR_A3);
+ vcpu->run->hypercall.args[4] = kvm_read_reg(vcpu, LOONGARCH_GPR_A4);
+ vcpu->run->hypercall.args[5] = kvm_read_reg(vcpu, LOONGARCH_GPR_A5);
+ vcpu->run->hypercall.flags = 0;
+ /*
+ * Set invalid return value by default
+ * Need user-mode VMM modify it
+ */
+ vcpu->run->hypercall.ret = KVM_HCALL_INVALID_CODE;
+ 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/vcpu.c b/arch/loongarch/kvm/vcpu.c
index d18a4a270415..8c46ad1872ee 100644
--- a/arch/loongarch/kvm/vcpu.c
+++ b/arch/loongarch/kvm/vcpu.c
@@ -1735,6 +1735,9 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
if (run->exit_reason == KVM_EXIT_LOONGARCH_IOCSR) {
if (!run->iocsr_io.is_write)
kvm_complete_iocsr_read(vcpu, run);
+ } else if (run->exit_reason == KVM_EXIT_HYPERCALL) {
+ kvm_write_reg(vcpu, LOONGARCH_GPR_A0, run->hypercall.ret);
+ update_pc(&vcpu->arch);
}
if (!vcpu->wants_to_run)
base-commit: 48f506ad0b683d3e7e794efa60c5785c4fdc86fa
--
2.39.3