or is this primarily a virtualization bug? http://hn.premii.com/#/article/16046636
"Bad news: the software mitigation is expensive The primary reason for the old Linux behaviour of mapping kernel memory in the same page tables as user memory is so that when the user’s code triggers a system call, fault, or an interrupt fires, it is not necessary to change the virtual memory layout of the running process. Since it is unnecessary to change the virtual memory layout, it is further unnecessary to flush highly performance-sensitive CPU caches that are dependant on that layout, primarily the Translation Lookaside Buffer. With the page table splitting patches merged, it becomes necessary for the kernel to flush these caches every time the kernel begins executing, and every time user code resumes executing. For some workloads, the effective total loss of the TLB lead around every system call leads to highly visible slowdowns: @grsecurity measured a simple case where Linux “du -s” suffered a 50% slowdown on a recent AMD CPU." -- Dave Täht CEO, TekLibre, LLC http://www.teklibre.com Tel: 1-669-226-2619 _______________________________________________ Cerowrt-devel mailing list Cerowrt-devel@lists.bufferbloat.net https://lists.bufferbloat.net/listinfo/cerowrt-devel
