linux-kernel - Re: [PATCH v2 00/14] KVM: x86: Remove emulation

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Date:   Tue, 17 Sep 2019 17:14:05 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Radim Krčmář <rkrcmar@...hat.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Liran Alon <liran.alon@...cle.com>
Subject: Re: [PATCH v2 00/14] KVM: x86: Remove emulation_result enums

On 27/08/19 23:40, Sean Christopherson wrote:
> Rework the emulator and its users to handle failure scenarios entirely
> within the emulator.
> 
> {x86,kvm}_emulate_instruction() currently returns a tri-state value to
> indicate success/continue, userspace exit needed, and failure.  The
> intent of returning EMULATE_FAIL is to let the caller handle failure in
> a manner that is appropriate for the current context.  In practice,
> the emulator has ended up with a mixture of failure handling, i.e.
> whether or not the emulator takes action on failure is dependent on the
> specific flavor of emulation.
> 
> The mixed handling has proven to be rather fragile, e.g. many flows
> incorrectly assume their specific flavor of emulation cannot fail or
> that the emulator sets state to report the failure back to userspace.
> 
> Move everything inside the emulator, piece by piece, so that the
> emulation routines can return '0' for exit to userspace and '1' for
> resume the guest, just like every other VM-Exit handler.
> 
> Patch 13/14 is a tangentially related bug fix that conflicts heavily with
> this series, so I tacked it on here.
> 
> Patch 14/14 documents the emulation types.  I added it as a separate
> patch at the very end so that the comments could reference the final
> state of the code base, e.g. incorporate the rule change for using
> EMULTYPE_SKIP that is introduced in patch 13/14.
> 
> v1:
>   - https://patchwork.kernel.org/cover/11110331/
> 
> v2:
>   - Collect reviews. [Vitaly and Liran]
>   - Squash VMware emultype changes into a single patch. [Liran]
>   - Add comments in VMX/SVM for VMware #GP handling. [Vitaly]
>   - Tack on the EPT misconfig bug fix.
>   - Add a patch to comment/document the emultypes. [Liran]
> 
> Sean Christopherson (14):
>   KVM: x86: Relocate MMIO exit stats counting
>   KVM: x86: Clean up handle_emulation_failure()
>   KVM: x86: Refactor kvm_vcpu_do_singlestep() to remove out param
>   KVM: x86: Don't attempt VMWare emulation on #GP with non-zero error
>     code
>   KVM: x86: Move #GP injection for VMware into x86_emulate_instruction()
>   KVM: x86: Add explicit flag for forced emulation on #UD
>   KVM: x86: Move #UD injection for failed emulation into emulation code
>   KVM: x86: Exit to userspace on emulation skip failure
>   KVM: x86: Handle emulation failure directly in kvm_task_switch()
>   KVM: x86: Move triple fault request into RM int injection
>   KVM: VMX: Remove EMULATE_FAIL handling in handle_invalid_guest_state()
>   KVM: x86: Remove emulation_result enums, EMULATE_{DONE,FAIL,USER_EXIT}
>   KVM: VMX: Handle single-step #DB for EMULTYPE_SKIP on EPT misconfig
>   KVM: x86: Add comments to document various emulation types
> 
>  arch/x86/include/asm/kvm_host.h |  40 +++++++--
>  arch/x86/kvm/mmu.c              |  16 +---
>  arch/x86/kvm/svm.c              |  62 ++++++--------
>  arch/x86/kvm/vmx/vmx.c          | 147 +++++++++++++-------------------
>  arch/x86/kvm/x86.c              | 133 ++++++++++++++++-------------
>  arch/x86/kvm/x86.h              |   2 +-
>  6 files changed, 195 insertions(+), 205 deletions(-)
> 

Queued, thanks (a couple conflicts had to be sorted out, but nothing
requiring a respin).

Paolo