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Re: XenServer and viridian
On Thu, 27 Mar 2025, Stephen Borrill wrote:
On Thu, 27 Mar 2025, Manuel Bouyer wrote:
On Thu, Mar 27, 2025 at 08:53:01AM +0000, Stephen Borrill wrote:
On Wed, 26 Mar 2025, Manuel Bouyer wrote:
On Wed, Mar 26, 2025 at 05:24:39PM +0000, Stephen Borrill wrote:
On XenServer/XCP-ng VMs can have 'Viridian enlightenments' enabled. This
is
used by Windows VMs to get some features that would otherwise require
Hyper-V, for instance, VM generation counter as used by Active Directory
to
spot it if is has been rolled back.
These shouldn't affect any non-Windows VMs, but NetBSD mistakenly thinks
it
is running on Hyper-V rather than Xen, so the PVH code is not enabled.
I tried the following naive patch:
--- sys/arch/x86/x86/identcpu.c 2 Feb 2025 14:51:59 -0000
1.123.4.2
+++ sys/arch/x86/x86/identcpu.c 26 Mar 2025 17:20:44 -0000
@@ -1132,8 +1132,22 @@
vm_guest = VM_GUEST_VMWARE;
else if (memcmp(hv_vendor, "Microsoft Hv", 12)
== 0) {
vm_guest = VM_GUEST_HV;
+ p = pmf_get_platform("system-vendor");
+ if (p != NULL) {
+ if (strncmp(p, "Xen", 3) == 0) {
+ /*
+ * XenServer VMs may
have
+ * Viridian
enlightenments
+ * enabled which may
make
+ * Hyper-V be falsely
matched
+ */
+ vm_guest =
VM_GUEST_XENHVM;
+ }
+ }
#if NHYPERV > 0
- hyperv_early_init();
+ if (vm_guest == VM_GUEST_HV) {
+ hyperv_early_init();
+ }
#endif
} else if (memcmp(hv_vendor, "KVMKVMKVM\0\0\0",
12) == 0)
vm_guest = VM_GUEST_KVM;
It correctly "Identified Guest XEN in HVM mode" instead of Hyper-C, but
immediately panicked in xen_hvm_init().
Is there a less naive patch I could try? :-)
Can you give more details about the panic ?
[ 1.0000000] NetBSD 10.1_STABLE (GENERIC) #6: Wed Mar 26 17:13:37 GMT
2025
[ 1.0000000]
root@builder10:/usr/work/obj/10/amd64/sys/arch/amd64/compile/GENERIC
[ 1.0000000] total memory = 1019 MB
[ 1.0000000] avail memory = 957 MB
[ 1.0000040] efi: systbl at pa 3f5ee018
[ 1.0000040] mainbus0 (root)
[ 1.0000040] Identified Guest XEN in HVM mode.
[ 1.0000040] fatal protection fault in supervisor mode
[ 1.0000040] trap type 4 code 0 rip 0xffffffff802499cd cs 0x8 rflags
0x246 cr2 0 ilevel 0x8 rsp 0xffffffff81d40cf0
[ 1.0000040] curlwp 0xffffffff8188b000 pid 0.0 lowest kstack
0xffffffff81d3b2c0
kernel: protection fault trap, code=0
Stopped in pid 0.0 (system) at netbsd:xen_hvm_init+0xad: wrmsr
xen_hvm_init() at netbsd:xen_hvm_init+0xad
So my guess is that it's failing in xen_init_hypercall_page(),
when doing:
wrmsr(descs[1], (uintptr_t)&hypercall_page - KERNBASE);
this means that when booting in this mode, the Xen interfaces are not
available to the guest.
When booting in this mode without the hack, do you see some unattached Xen
PCI devices in the dmesg ?
Yes:
# dmesg | grep -i xen
ACPI: RSDP 0x000000003F5FA014 000024 (v02 Xen )
ACPI: XSDT 0x000000003F5F90E8 00004C (v01 Xen HVM 00000000
01000013)
ACPI: FACP 0x000000003F5F8000 0000F4 (v04 Xen HVM 00000000 HVML
00000000)
ACPI: DSDT 0x000000003E50C000 0092A3 (v02 Xen HVM 00000000 INTL
20160527)
ACPI: APIC 0x000000003F5F7000 000260 (v02 Xen HVM 00000000 HVML
00000000)
ACPI: HPET 0x000000003F5F6000 000038 (v01 Xen HVM 00000000 HVML
00000000)
ACPI: WAET 0x000000003F5F5000 000028 (v01 Xen HVM 00000000 HVML
00000000)
acpi0: X/RSDT: OemId < Xen, HVM,00000000>, AslId < ,01000013>
XenSource, Inc. Xen Platform Device (undefined, subclass 0x80, revision 0x01)
at pci0 dev 3 function 0 not configured
I also tried FreeBSD 14.2 with exactly the same config and they get it
right.
Hyper-V Version: 0.0.0 [SP0]
Features=0x870<APIC,HYPERCALL,VPINDEX,TMFREQ>
PM Features=0x0 [C0]
Features3=0x8<PCPUDPE>
XEN: Hypervisor version 4.13 detected.
CPU: Intel(R) Xeon(R) CPU E5-2620 0 @ 2.00GHz (2000.14-MHz K8-class CPU)
Origin="GenuineIntel" Id=0x206d7 Family=0x6 Model=0x2d Stepping=7
Features=0x1fc3fbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,ACPI,MMX,FXSR,SSE,SSE2,SS,HTT>
Features2=0x9fba2203<SSE3,PCLMULQDQ,SSSE3,CX16,PCID,SSE4.1,SSE4.2,x2APIC,POPCNT,TSCDLT,AESNI,XSAVE,OSXSAVE,AVX,HV>
AMD Features=0x2c100800<SYSCALL,NX,Page1GB,RDTSCP,LM>
AMD Features2=0x1<LAHF>
Structured Extended Features3=0x9c000400<MD_CLEAR,IBPB,STIBP,L1DFL,SSBD>
XSAVE Features=0x1<XSAVEOPT>
AMD Extended Feature Extensions ID EBX=0x1000<IBPB>
Hypervisor: Origin = "Microsoft Hv"
real memory = 1069547520 (1020 MB)
avail memory = 996438016 (950 MB)
Event timer "LAPIC" quality 100
ACPI APIC Table: <Xen HVM>
[snip]
xenpv0: <Xen PV bus>
granttable0: <Xen Grant-table Device> on xenpv0
xen_et0: <Xen PV Clock> on xenpv0
Event timer "XENTIMER" frequency 1000000000 Hz quality 950
Timecounter "XENTIMER" frequency 1000000000 Hz quality 950
xen_et0: registered as a time-of-day clock, resolution 0.000001s
xenstore0: <XenStore> on xenpv0
xsd_dev0: <Xenstored user-space device> on xenpv0
evtchn0: <Xen event channel user-space device> on xenpv0
privcmd0: <Xen privileged interface user-space device> on xenpv0
gntdev0: <Xen grant-table user-space device> on xenpv0
debug0: <Xen debug handler> on xenpv0
Timecounters tick every 10.000 msec
xenballoon0: <Xen Balloon Device> on xenstore0
xctrl0: <Xen Control Device> on xenstore0
ugen0.1: <Intel UHCI root HUB> at usbus0
uhub0 on usbus0
uhub0: <Intel UHCI root HUB, class 9/0, rev 1.00/1.00, addr 1> on usbus0
xs_dev0: <Xenstore user-space device> on xenstore0
xenbusb_front0: <Xen Frontend Devices> on xenstore0
xn0: <Virtual Network Interface> at device/vif/0 on xenbusb_front0
xn0: Ethernet address: 96:fe:50:f8:b9:e6
xenbusb_back0: <Xen Backend Devices> on xenstore0
xn0: backend features: feature-sg feature-gso-tcp4
xbd0: 10240MB <Virtual Block Device> at device/vbd/768 on xenbusb_front0
xbd0: attaching as ada0
xbd0: features: write_barrier
xbd0: synchronize cache commands enabled.
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