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Subject: Re: [PATCH v3 0/9] KVM: Support guest MAXPHYADDR < host MAXPHYADDR
To:     Mohammed Gamal <mgamal@redhat.com>, kvm@vger.kernel.org
Cc:     linux-kernel@vger.kernel.org, vkuznets@redhat.com,
        sean.j.christopherson@intel.com, wanpengli@tencent.com,
        jmattson@google.com, joro@8bytes.org
References: <20200710154811.418214-1-mgamal@redhat.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <69f44e48-4609-ff64-56a9-ce72e1f483fa@redhat.com>
Date:   Fri, 10 Jul 2020 19:49:12 +0200
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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