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From: Chenyi Qiang <chenyi.qiang@intel.com>
To: Paolo Bonzini <pbonzini@redhat.com>,
	Sean Christopherson <seanjc@google.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	Xiaoyao Li <xiaoyao.li@intel.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH v2 0/3] Add KVM support for bus lock debug exception
Date: Tue,  2 Feb 2021 17:04:30 +0800	[thread overview]
Message-ID: <20210202090433.13441-1-chenyi.qiang@intel.com> (raw)

A bus lock is acquired either through split locked access to writeback
(WB) memory or by using locks to uncacheable (UC) memory. This is
typically > 1000 cycles slower than atomic opertaion within a cache
line. It also disrupts performance on other cores.

Bus lock debug exception is a sub-feature of bus lock detection. It is
an ability to notify the kernel by an #DB trap after the instruction
acquires a bus lock when CPL>0. This allows the kernel to enforce user
application throttling or mitigatioins.

Expose the bus lock debug exception to guest by the enumeration of
CPUID.(EAX=7,ECX=0).ECX[24]. Software in guest can enable these
exceptions by setting the DEBUGCTLMSR_BUS_LOCK_DETECT(bit 2) of

The bus lock #DB exception can also be intercepted by the VMM and
identified through the bit 11 of the exit qualification at VM exit. The
bit 11 (DR6_BUS_LOCK) of DR6 register is introduced to indicate a bus
lock #DB exception. DR6_BUS_LOCK has formerly always been 1 and delivery
of a bus lock #DB clears it. The VMM should emulate the exceptions by
clearing the bit 11 of the guest DR6.

Bus lock debug exception kernel patches are available at:

Document for Bus Lock Detection is now available at the latest "Intel
Architecture Instruction Set Extensions Programming Reference".

Document Link:



- rename the DR6_INIT to DR6_LOW_ACTIVE suggested by Paolo and split it
  out as a new commit.
- KVM v1:https://lore.kernel.org/lkml/20210108064924.1677-1-chenyi.qiang@intel.com

Chenyi Qiang (3):
  KVM: X86: Rename DR6_INIT to DR6_ACTIVE_LOW
  KVM: X86: Add support for the emulation of DR6_BUS_LOCK bit
  KVM: X86: Expose bus lock debug exception to guest

 arch/x86/include/asm/kvm_host.h | 14 +++++++--
 arch/x86/kvm/cpuid.c            |  3 +-
 arch/x86/kvm/emulate.c          |  2 +-
 arch/x86/kvm/svm/nested.c       |  2 +-
 arch/x86/kvm/svm/svm.c          |  6 ++--
 arch/x86/kvm/vmx/nested.c       |  4 +--
 arch/x86/kvm/vmx/vmx.c          | 27 ++++++++++++++---
 arch/x86/kvm/x86.c              | 52 +++++++++++++++------------------
 arch/x86/kvm/x86.h              |  2 ++
 9 files changed, 69 insertions(+), 43 deletions(-)


             reply	other threads:[~2021-02-02  9:02 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-02  9:04 Chenyi Qiang [this message]
2021-02-02  9:04 ` [PATCH v2 1/3] KVM: X86: Rename DR6_INIT to DR6_ACTIVE_LOW Chenyi Qiang
2021-02-02 14:49   ` Paolo Bonzini
2021-02-02 15:02     ` Xiaoyao Li
2021-02-02 16:05       ` Paolo Bonzini
2021-04-02  8:53         ` Xiaoyao Li
2021-04-02  9:01           ` Paolo Bonzini
2021-05-06  8:21             ` Chenyi Qiang
2021-05-06 10:19               ` Paolo Bonzini
2021-02-02  9:04 ` [PATCH v2 2/3] KVM: X86: Add support for the emulation of DR6_BUS_LOCK bit Chenyi Qiang
2021-02-02  9:04 ` [PATCH v2 3/3] KVM: X86: Expose bus lock debug exception to guest Chenyi Qiang

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