linux-kernel - Re: [PATCH v5 0/4] Add bus lock VM exit support

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Message-ID: <95477feb-b92d-8f26-fc59-11bbdcc8354b@redhat.com>
Date:   Mon, 25 Jan 2021 19:00:58 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Chenyi Qiang <chenyi.qiang@...el.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Xiaoyao Li <xiaoyao.li@...el.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 0/4] Add bus lock VM exit support

On 06/11/20 10:03, Chenyi Qiang wrote:
> This patch series add the support for bus lock VM exit in KVM. It is a
> sub-feature of bus lock detection. When it is enabled by the VMM, the
> processor generates a "Bus Lock" VM exit following execution of an
> instruction if the processor detects that one or more bus locks were
> caused the instruction was being executed (due to either direct access
> by the instruction or stuffed accesses like through A/D updates).
> 
> Bus lock VM exit will introduce a new modifier bit (bit 26) in
> exit_reason field in VMCS which indicates bus lock VM exit is preempted
> by a higher priority VM exit. The first patch is to apply Sean's
> refactor for vcpu_vmx.exit_reason as a preparation patch for bus lock
> VM exit support.
> 
> The second patch is the refactor for vcpu->run->flags. Bus lock VM exit
> will introduce a new field in the flags to inform the userspace that
> there's a bus lock detected in guest. It's also a preparation patch.
> 
> The third patch is the concrete enabling working for bus lock VM exit.
> Add the support to set the capability to enable bus lock VM exit. The
> current implementation is just exiting to userspace when handling the
> bus lock detected in guest.
> 
> The detail of throttling policy in user space is still to be discussed.
> We may enforce ratelimit on bus lock in guest, inject some sleep time,
> or... We hope to get more ideas on this.
> 
> Document for Bus Lock Detection is now available at the latest "Intel
> Architecture Instruction Set Extensions Programming Reference".
> 
> Document Link:
> https://software.intel.com/content/www/us/en/develop/download/intel-architecture-instruction-set-extensions-programming-reference.html
> 
> ---
> 
> Changelogs
> 
> v4->v5:
> - rebase on top on v5.10-rc2
> - add preparation patch that reset the vcpu->run->flags at the beginning
>    of the vcpu_run.(Suggested by Sean)
> - set the KVM_RUN_BUS_LOCK for all bus lock exit to avoid checking both
>    exit_reason and run->flags
> - add the document to introduce the new kvm capability
>    (KVM_CAP_X86_BUS_LOCK_EXIT)
> - v4:https://lore.kernel.org/lkml/20201012033542.4696-1-chenyi.qiang@intel.com/
> 
> 
> v3->v4:
> - rebase on top of v5.9
> - some code cleanup.
> - v3:https://lore.kernel.org/lkml/20200910083751.26686-1-chenyi.qiang@intel.com/
> 
> v2->v3:
> - use a bitmap to get/set the capability of bus lock detection. we support
>    exit and off mode currently.
> - put the handle of exiting to userspace in vmx.c, thus no need to
>    define a shadow to track vmx->exit_reason.bus_lock_detected.
> - remove the vcpu->stats.bus_locks since every bus lock exits to userspace.
> - v2:https://lore.kernel.org/lkml/20200817033604.5836-1-chenyi.qiang@intel.com/
> 
> v1->v2:
> - resolve Vitaly's comment to introduce the KVM_EXIT_BUS_LOCK and a
>    capability to enable it.
> - add the support to exit to user space when handling bus locks.
> - extend the vcpu->run->flags to indicate bus lock detected for other
>    exit reasons when exiting to user space.
> - v1:https://lore.kernel.org/lkml/20200628085341.5107-1-chenyi.qiang@intel.com/
> 
> ---
> 
> Chenyi Qiang (3):
>    KVM: X86: Reset the vcpu->run->flags at the beginning of vcpu_run
>    KVM: VMX: Enable bus lock VM exit
>    KVM: X86: Add the Document for KVM_CAP_X86_BUS_LOCK_EXIT
> 
> Sean Christopherson (1):
>    KVM: VMX: Convert vcpu_vmx.exit_reason to a union
> 
>   Documentation/virt/kvm/api.rst     |  45 ++++++++++++-
>   arch/x86/include/asm/kvm_host.h    |   7 ++
>   arch/x86/include/asm/vmx.h         |   1 +
>   arch/x86/include/asm/vmxfeatures.h |   1 +
>   arch/x86/include/uapi/asm/kvm.h    |   1 +
>   arch/x86/include/uapi/asm/vmx.h    |   4 +-
>   arch/x86/kvm/vmx/capabilities.h    |   6 ++
>   arch/x86/kvm/vmx/nested.c          |  42 +++++++-----
>   arch/x86/kvm/vmx/vmx.c             | 105 +++++++++++++++++++----------
>   arch/x86/kvm/vmx/vmx.h             |  25 ++++++-
>   arch/x86/kvm/x86.c                 |  28 +++++++-
>   include/uapi/linux/kvm.h           |   5 ++
>   12 files changed, 214 insertions(+), 56 deletions(-)
> 

Queued, thanks.  I have replaced KVM_RUN_BUS_LOCK with 
KVM_RUN_X86_BUS_LOCK, though.

Paolo