[PATCH v3 0/9] KVM: Support guest MAXPHYADDR < host MAXPHYADDR

Mohammed Gamal
2020-07-10T15:48:23Z

When EPT is enabled, KVM does not really look at guest physical
address size. Address bits above maximum physical memory size are reserved.
Because KVM does not look at these guest physical addresses, it currently
effectively supports guest physical address sizes equal to the host.

This can be problem when having a mixed setup of machines with 5-level page
tables and machines with 4-level page tables, as live migration can change
MAXPHYADDR while the guest runs, which can theoretically introduce bugs.

In this patch series we add checks on guest physical addresses in EPT
violation/misconfig and NPF vmexits and if needed inject the proper
page faults in the guest.

A more subtle issue is when the host MAXPHYADDR is larger than that of the
guest. Page faults caused by reserved bits on the guest won't cause an EPT
violation/NPF and hence we also check guest MAXPHYADDR and add PFERR_RSVD_MASK
error code to the page fault if needed.

----

Changes from v2:
- Drop support for this feature on AMD processors after discussion with AMD

Mohammed Gamal (5):
KVM: x86: Add helper functions for illegal GPA checking and page fault
injection
KVM: x86: mmu: Move translate_gpa() to mmu.c
KVM: x86: mmu: Add guest physical address check in translate_gpa()
KVM: VMX: Add guest physical address check in EPT violation and
misconfig
KVM: x86: SVM: VMX: Make GUEST_MAXPHYADDR < HOST_MAXPHYADDR support
configurable

Paolo Bonzini (4):
KVM: x86: rename update_bp_intercept to update_exception_bitmap
KVM: x86: update exception bitmap on CPUID changes
KVM: VMX: introduce vmx_need_pf_intercept
KVM: VMX: optimize #PF injection when MAXPHYADDR does not match

arch/x86/include/asm/kvm_host.h | 10 ++------
arch/x86/kvm/cpuid.c | 2 ++
arch/x86/kvm/mmu.h | 6 +++++
arch/x86/kvm/mmu/mmu.c | 12 +++++++++
arch/x86/kvm/svm/svm.c | 22 +++++++++++++---
arch/x86/kvm/vmx/nested.c | 28 ++++++++++++--------
arch/x86/kvm/vmx/vmx.c | 45 +++++++++++++++++++++++++++++----
arch/x86/kvm/vmx/vmx.h | 6 +++++
arch/x86/kvm/x86.c | 29 ++++++++++++++++++++-
arch/x86/kvm/x86.h | 1 +
include/uapi/linux/kvm.h | 1 +
11 files changed, 133 insertions(+), 29 deletions(-)

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2.26.2