You have been subscribed to a public bug: 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 operation within a cache line. It also disrupts performance on other cores (which must wait for the bus lock to be released before their memory operations).
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 mitigations. A logical processor can be configured to generate a debug exception (#DB) following acquisition of a bus lock. Software enables those debug exceptions by setting bit 2 of the IA32_DEBUGCTL MSR. The CPU enumerates this feature using CPUID.(EAX=7, ECX=0).ECX[24]. A debug exception due to acquistion of a bus lock is reported as a trap following execution of the instruction acquiring the bus lock. The processor identifies such debug exceptions using bit 11 of DR6: delivery of a bus-lock #DB clears DR6[11]. Linux 5.13 ** Affects: linux (Ubuntu) Importance: Undecided Status: New -- KVM Bus Lock Debug Exception https://bugs.launchpad.net/bugs/1954469 You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp