Re: [PATCH v4 00/28] KVM: combined patchset for MBEC/GMET support

David Riley
2026-04-29T13:05:51Z

Hi Paolo, Hi Jon,

Thanks again Paolo, for the new version of this Patch Series.

I have once again tested this patch series (v4) focusing on the updated
implementation of GMET on the AMD Platform using Proxmox VE (based
on Debian Trixie) with a Windows Server guest
(24H2, Build 26100.1742).

Setup:
- Host CPU: AMD EPYC 7302P
- Kernel: mainline 7.1-rc1 (with v4 patches applied)
- QEMU: downstream 10.2.1 with the backported commit for the gmet
option [0].
- virtio-win: 0.1.271

I started the Windows VM and verified that GMET was detected
correctly.
AvailableSecurityProperties [1]: 1,2,4,5,7

Windows Guest:
After the initial installation and verification I enabled
Virtualization-Based Security (VBS) and Hypervisor-Protected Code
Integrity (HVCI).

I set the following in the Group Policy Editor (DeviceGuard):
* Select Platform Security Level: Secure Boot
* Virtualization Based Protection of Code Integrity: Enabled without
lock
* Require UEFI Memory Attributes Table: Checked

I tried to launch the Windows Guest with these QEMU CPU options:
-cpu 'host,+kvm_pv_eoi,+kvm_pv_unhalt,level=30'

These flags worked with the last patch series (v3) without any issues
[2][3].

I observed the following:
The guest now never actually boots into Windows. It gets stuck before
that and therefore does not even enter Windows Recovery.

I found the following log in the journal:
Apr 29 13:44:55 jura2 kernel: kvm_amd: kvm [29717]: vcpu0, guest rIP:
0xfffff83560f3b225 Unhandled WRMSR(0xc0010115) = 0x0

the same messages also appeared in dmesg:
[ 1910.476609] kvm_amd: kvm [8755]: vcpu0, guest rIP:
0xfffff851f793b225 Unhandled WRMSR(0xc0010115) = 0x0

I also did a trace using `trace-cmd record -e kvm` and observed that
the cpu seems to be stuck in a infinite loop. Snippet of the output:

CPU 0/KVM-29834 [020] .....  8801.135700: kvm_page_fault:      vcpu 0 rip 0xfffff83560f8f6a0 address 0x00000001011e9f80 error_code 0x200000007
CPU 0/KVM-29834 [020] d..1.  8801.135701: kvm_entry:      vcpu 0 rip 0xfffff83560f8f6a0
CPU 0/KVM-29834 [020] d..1.  8801.135702: kvm_exit:      reason EXIT_NPF rip 0xfffff83560f8f6a0 info 200000007 1011e9f80
CPU 0/KVM-29834 [020] .....  8801.135702: kvm_nested_vmexit:    <CANT FIND FIELD rip>vcpu 0 reason npf rip 0xfffff83560f8f6a0 info1 0x0000000200000007 info2 0x00000001011e9f80 intr_info 0x00000000 error_code 0x00000000 requests 0x0000000000000000
CPU 0/KVM-29834 [020] .....  8801.135703: kvm_page_fault:      vcpu 0 rip 0xfffff83560f8f6a0 address 0x00000001011e9f80 error_code 0x200000007
CPU 0/KVM-29834 [020] d..1.  8801.135704: kvm_entry:      vcpu 0 rip 0xfffff83560f8f6a0
CPU 0/KVM-29834 [020] d..1.  8801.135705: kvm_exit:      reason EXIT_NPF rip 0xfffff83560f8f6a0 info 200000007 1011e9f80
CPU 0/KVM-29834 [020] .....  8801.135705: kvm_nested_vmexit:    <CANT FIND FIELD rip>vcpu 0 reason npf rip 0xfffff83560f8f6a0 info1 0x0000000200000007 info2 0x00000001011e9f80 intr_info 0x00000000 error_code 0x00000000 requests 0x0000000000000000

Could this be related to the new patch 24?
Are there certain flags or enhancements I could try?

Please let me know if you need some additional debug output.

Best regards,
David

[0] https://gitlab.com/qemu-project/qemu/-/commit/746a823a17f25393cc8c0cd1257f6dcef757bc09
[1] https://learn.microsoft.com/en-us/windows/security/hardware-security/enable-virtualization-based-protection-of-code-integrity?tabs=security
[2] https://lore.kernel.org/kvm/20260408154217.458420-1-pbonzini@redhat.com/
[3] https://lore.kernel.org/kvm/c91391f4-57b8-4bad-aba8-2c47c285ab27@proxmox.com/

On 4/28/26 1:33 PM, Paolo Bonzini wrote:
> I will send you to v3 (https://lore.kernel.org/kvm/20260408154217.458420-1-pbonzini@redhat.com/)
> for the description of the series, and leave a short list of changes:
>
> - patch 15: clear enable_mbec = 0 if enable_ept == 0
> - patches 23-27: adjust for rename of nested_ctl to misc_ctl
> - patch 24: new
> - patch 27: disable svm_get_cpl for SEV-ES/SEV-SNP
> - patch 28: fix commit message reference to __nested_svm_check_controls
>
> (patch 24 is the only major bugfix).
>
> Thanks,
>
> Paolo
>
> Jon Kohler (5):
> KVM: TDX/VMX: rework EPT_VIOLATION_EXEC_FOR_RING3_LIN into PROT_MASK
> KVM: x86/mmu: remove SPTE_PERM_MASK
> KVM: x86/mmu: free up bit 10 of PTEs in preparation for MBEC
> KVM: nVMX: advertise MBEC to nested guests
> KVM: nVMX: allow MBEC with EVMCS
>
> Paolo Bonzini (23):
> KVM: x86/mmu: shuffle high bits of SPTEs in preparation for MBEC
> KVM: x86/mmu: remove SPTE_EPT_*
> KVM: x86/mmu: merge make_spte_{non,}executable
> KVM: x86/mmu: rename and clarify BYTE_MASK
> KVM: x86/mmu: introduce ACC_READ_MASK
> KVM: x86/mmu: separate more EPT/non-EPT permission_fault()
> KVM: x86/mmu: pass PFERR_GUEST_PAGE/FINAL_MASK to kvm_translate_gpa
> KVM: x86/mmu: pass pte_access for final nGPA->GPA walk
> KVM: x86: make translate_nested_gpa vendor-specific
> KVM: x86/mmu: split XS/XU bits for EPT
> KVM: x86/mmu: move cr4_smep to base role
> KVM: VMX: enable use of MBEC
> KVM: nVMX: pass advanced EPT violation vmexit info to guest
> KVM: nVMX: pass PFERR_USER_MASK to MMU on EPT violations
> KVM: x86/mmu: add support for MBEC to EPT page table walks
> KVM: x86/mmu: propagate access mask from root pages down
> KVM: x86/mmu: introduce cpu_role bit for availability of PFEC.I/D
> KVM: SVM: add GMET bit definitions
> KVM: x86/mmu: set CR0.WP=1 for shadow NPT MMU
> KVM: x86/mmu: add support for GMET to NPT page table walks
> KVM: SVM: enable GMET and set it in MMU role
> KVM: SVM: work around errata 1218
> KVM: nSVM: enable GMET for guests
>
> Documentation/virt/kvm/x86/mmu.rst | 10 +-
> arch/x86/include/asm/cpufeatures.h | 1 +
> arch/x86/include/asm/kvm-x86-ops.h | 1 +
> arch/x86/include/asm/kvm_host.h | 48 ++++++---
> arch/x86/include/asm/svm.h | 1 +
> arch/x86/include/asm/vmx.h | 14 ++-
> arch/x86/kvm/hyperv.c | 4 +-
> arch/x86/kvm/mmu.h | 30 ++++--
> arch/x86/kvm/mmu/mmu.c | 168 ++++++++++++++++++++---------
> arch/x86/kvm/mmu/mmutrace.h | 19 ++--
> arch/x86/kvm/mmu/paging_tmpl.h | 73 ++++++++-----
> arch/x86/kvm/mmu/spte.c | 74 +++++++------
> arch/x86/kvm/mmu/spte.h | 70 ++++++------
> arch/x86/kvm/mmu/tdp_mmu.c | 6 +-
> arch/x86/kvm/svm/nested.c | 37 ++++++-
> arch/x86/kvm/svm/svm.c | 31 ++++++
> arch/x86/kvm/svm/svm.h | 1 +
> arch/x86/kvm/vmx/capabilities.h | 12 ++-
> arch/x86/kvm/vmx/common.h | 20 ++--
> arch/x86/kvm/vmx/hyperv_evmcs.h | 1 +
> arch/x86/kvm/vmx/main.c | 9 ++
> arch/x86/kvm/vmx/nested.c | 46 +++++++-
> arch/x86/kvm/vmx/tdx.c | 2 +-
> arch/x86/kvm/vmx/vmx.c | 27 ++++-
> arch/x86/kvm/vmx/vmx.h | 1 +
> arch/x86/kvm/vmx/x86_ops.h | 1 +
> arch/x86/kvm/x86.c | 18 +---
> 27 files changed, 505 insertions(+), 220 deletions(-)
>