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[PATCH v13 06/60] i386/kvm: Set Xen vCPU ID in KVM
From: |
David Woodhouse |
Subject: |
[PATCH v13 06/60] i386/kvm: Set Xen vCPU ID in KVM |
Date: |
Thu, 23 Feb 2023 12:45:19 +0000 |
From: David Woodhouse <dwmw@amazon.co.uk>
There are (at least) three different vCPU ID number spaces. One is the
internal KVM vCPU index, based purely on which vCPU was chronologically
created in the kernel first. If userspace threads are all spawned and
create their KVM vCPUs in essentially random order, then the KVM indices
are basically random too.
The second number space is the APIC ID space, which is consistent and
useful for referencing vCPUs. MSIs will specify the target vCPU using
the APIC ID, for example, and the KVM Xen APIs also take an APIC ID
from userspace whenever a vCPU needs to be specified (as opposed to
just using the appropriate vCPU fd).
The third number space is not normally relevant to the kernel, and is
the ACPI/MADT/Xen CPU number which corresponds to cs->cpu_index. But
Xen timer hypercalls use it, and Xen timer hypercalls *really* want
to be accelerated in the kernel rather than handled in userspace, so
the kernel needs to be told.
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>
---
target/i386/kvm/kvm.c | 5 +++++
target/i386/kvm/xen-emu.c | 28 ++++++++++++++++++++++++++++
target/i386/kvm/xen-emu.h | 1 +
3 files changed, 34 insertions(+)
diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
index 2b3daabf7b..165fa5232d 100644
--- a/target/i386/kvm/kvm.c
+++ b/target/i386/kvm/kvm.c
@@ -1869,6 +1869,11 @@ int kvm_arch_init_vcpu(CPUState *cs)
}
}
+ r = kvm_xen_init_vcpu(cs);
+ if (r) {
+ return r;
+ }
+
kvm_base += 0x100;
#else /* CONFIG_XEN_EMU */
/* This should never happen as kvm_arch_init() would have died first.
*/
diff --git a/target/i386/kvm/xen-emu.c b/target/i386/kvm/xen-emu.c
index 34d5bc1bc9..4883b95d9d 100644
--- a/target/i386/kvm/xen-emu.c
+++ b/target/i386/kvm/xen-emu.c
@@ -52,6 +52,34 @@ int kvm_xen_init(KVMState *s, uint32_t hypercall_msr)
return 0;
}
+int kvm_xen_init_vcpu(CPUState *cs)
+{
+ int err;
+
+ /*
+ * The kernel needs to know the Xen/ACPI vCPU ID because that's
+ * what the guest uses in hypercalls such as timers. It doesn't
+ * match the APIC ID which is generally used for talking to the
+ * kernel about vCPUs. And if vCPU threads race with creating
+ * their KVM vCPUs out of order, it doesn't necessarily match
+ * with the kernel's internal vCPU indices either.
+ */
+ if (kvm_xen_has_cap(EVTCHN_SEND)) {
+ struct kvm_xen_vcpu_attr va = {
+ .type = KVM_XEN_VCPU_ATTR_TYPE_VCPU_ID,
+ .u.vcpu_id = cs->cpu_index,
+ };
+ err = kvm_vcpu_ioctl(cs, KVM_XEN_VCPU_SET_ATTR, &va);
+ if (err) {
+ error_report("kvm: Failed to set Xen vCPU ID attribute: %s",
+ strerror(-err));
+ return err;
+ }
+ }
+
+ return 0;
+}
+
uint32_t kvm_xen_get_caps(void)
{
return kvm_state->xen_caps;
diff --git a/target/i386/kvm/xen-emu.h b/target/i386/kvm/xen-emu.h
index 2101df0182..d62f1d8ed8 100644
--- a/target/i386/kvm/xen-emu.h
+++ b/target/i386/kvm/xen-emu.h
@@ -24,5 +24,6 @@
#define XEN_VERSION(maj, min) ((maj) << 16 | (min))
int kvm_xen_init(KVMState *s, uint32_t hypercall_msr);
+int kvm_xen_init_vcpu(CPUState *cs);
#endif /* QEMU_I386_KVM_XEN_EMU_H */
--
2.39.0
- [PATCH v13 00/60] Xen HVM support under KVM, David Woodhouse, 2023/02/23
- [PATCH v13 05/60] i386/kvm: handle Xen HVM cpuid leaves, David Woodhouse, 2023/02/23
- [PATCH v13 53/60] hw/xen: Automatically add xen-platform PCI device for emulated Xen guests, David Woodhouse, 2023/02/23
- [PATCH v13 10/60] i386/xen: implement HYPERVISOR_xen_version, David Woodhouse, 2023/02/23
- [PATCH v13 47/60] i386/xen: handle PV timer hypercalls, David Woodhouse, 2023/02/23
- [PATCH v13 22/60] i386/xen: handle VCPUOP_register_vcpu_time_info, David Woodhouse, 2023/02/23
- [PATCH v13 20/60] i386/xen: implement HYPERVISOR_vcpu_op, David Woodhouse, 2023/02/23
- [PATCH v13 06/60] i386/kvm: Set Xen vCPU ID in KVM,
David Woodhouse <=
- [PATCH v13 37/60] hw/xen: Implement EVTCHNOP_bind_vcpu, David Woodhouse, 2023/02/23
- [PATCH v13 38/60] hw/xen: Implement EVTCHNOP_reset, David Woodhouse, 2023/02/23
- [PATCH v13 30/60] hw/xen: Implement EVTCHNOP_close, David Woodhouse, 2023/02/23
- [PATCH v13 09/60] i386/xen: handle guest hypercalls, David Woodhouse, 2023/02/23
- [PATCH v13 25/60] i386/xen: implement HVMOP_set_evtchn_upcall_vector, David Woodhouse, 2023/02/23
- [PATCH v13 35/60] hw/xen: Implement EVTCHNOP_alloc_unbound, David Woodhouse, 2023/02/23
- [PATCH v13 45/60] i386/xen: Implement HYPERVISOR_grant_table_op and GNTTABOP_[gs]et_verson, David Woodhouse, 2023/02/23
- [PATCH v13 08/60] xen-platform: allow its creation with XEN_EMULATE mode, David Woodhouse, 2023/02/23
- [PATCH v13 07/60] xen-platform: exclude vfio-pci from the PCI platform unplug, David Woodhouse, 2023/02/23
- [PATCH v13 42/60] kvm/i386: Add xen-gnttab-max-frames property, David Woodhouse, 2023/02/23