linux-kernel - Re: [PATCH v3 0/9] KVM: nSVM: fixes for CR3/MMU switch upon nested guest entry/exit

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Date:   Thu, 9 Jul 2020 20:01:05 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Junaid Shahid <junaids@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 0/9] KVM: nSVM: fixes for CR3/MMU switch upon nested
 guest entry/exit

On 09/07/20 16:53, Vitaly Kuznetsov wrote:
> This is a successor of "[PATCH v2 0/3] KVM: nSVM: fix #TF from CR3 switch
> when entering guest" and "[PATCH] KVM: x86: drop erroneous mmu_check_root()
> from fast_pgd_switch()".
> 
> The snowball is growing fast! It all started with an intention to fix
> the particular 'tripple fault' issue (now fixed by PATCH7) but now we
> also get rid of unconditional kvm_mmu_reset_context() upon nested guest
> entry/exit and make the code resemble nVMX. There is still a huge room
> for further improvement (proper error propagation, removing unconditional
> MMU sync/TLB flush,...) but at least we're making some progress.
> 
> Tested with kvm selftests/kvm-unit-tests and by running nested Hyper-V
> on KVM. The series doesn't seem to introduce any new issues.

Looks like a v4 is needed but we're converging at least, it won't have
27 patches. :)

> Vitaly Kuznetsov (9):
>   KVM: nSVM: split kvm_init_shadow_npt_mmu() from kvm_init_shadow_mmu()
>   KVM: nSVM: stop dereferencing vcpu->arch.mmu to get the context in
>     kvm_init_shadow{,_npt}_mmu()
>   KVM: nSVM: reset nested_run_pending upon nested_svm_vmrun_msrpm()
>     failure
>   KVM: nSVM: prepare to handle errors from enter_svm_guest_mode()
>   KVM: nSVM: introduce nested_svm_load_cr3()
>   KVM: nSVM: move kvm_set_cr3() after nested_svm_uninit_mmu_context()
>   KVM: nSVM: implement nested_svm_load_cr3() and use it for host->guest
>     switch
>   KVM: nSVM: use nested_svm_load_cr3() on guest->host switch
>   KVM: x86: drop superfluous mmu_check_root() from fast_pgd_switch()
> 
>  arch/x86/kvm/mmu.h        |   3 +-
>  arch/x86/kvm/mmu/mmu.c    |  39 ++++++++++----
>  arch/x86/kvm/svm/nested.c | 108 ++++++++++++++++++++++++++++----------
>  arch/x86/kvm/svm/svm.c    |   6 ++-
>  arch/x86/kvm/svm/svm.h    |   4 +-
>  5 files changed, 116 insertions(+), 44 deletions(-)
>