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

Paolo Bonzini
2020-07-10T17:49:21Z

On 10/07/20 17:48, Mohammed Gamal wrote:
> 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(-)
>

Queued, thanks (I'll look at it more closely when I'm back, but at least
people can play with it).

Paolo