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 MSR_IA32_DEBUTCTL. This patch series add the MSR handling for DEBUGCTLMSR_BUS_LOCK_DETECT. The bus lock #DB exception can alse 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. The kernel RFC patch set for bus lock debug exception is available at https://lore.kernel.org/lkml/20201111192048.2602065-1-fenghua.yu@xxxxxxxxx/ 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 Chenyi Qiang (2): 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 | 5 ++-- arch/x86/kvm/cpuid.c | 3 ++- arch/x86/kvm/emulate.c | 2 +- arch/x86/kvm/svm/svm.c | 6 ++--- arch/x86/kvm/vmx/nested.c | 2 +- arch/x86/kvm/vmx/vmx.c | 29 +++++++++++++++++++--- arch/x86/kvm/x86.c | 44 ++++++++++++++------------------- arch/x86/kvm/x86.h | 2 ++ 8 files changed, 56 insertions(+), 37 deletions(-) -- 2.17.1
