1. 15 Mar, 2021 2 commits
    • Peter Zijlstra's avatar
      objtool/x86: Use asm/nops.h · 301cddc2
      Peter Zijlstra authored
      Since the kernel will rely on a single canonical set of NOPs, make sure
      objtool uses the exact same ones.
      Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
      Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
      Link: https://lkml.kernel.org/r/20210312115749.136357911@infradead.org
      301cddc2
    • Peter Zijlstra's avatar
      x86: Remove dynamic NOP selection · a89dfde3
      Peter Zijlstra authored
      This ensures that a NOP is a NOP and not a random other instruction that
      is also a NOP. It allows simplification of dynamic code patching that
      wants to verify existing code before writing new instructions (ftrace,
      jump_label, static_call, etc..).
      
      Differentiating on NOPs is not a feature.
      
      This pessimises 32bit (DONTCARE) and 32bit on 64bit CPUs (CARELESS).
      32bit is not a performance target.
      
      Everything x86_64 since AMD K10 (2007) and Intel IvyBridge (2012) is
      fine with using NOPL (as opposed to prefix NOP). And per FEATURE_NOPL
      being required for x86_64, all x86_64 CPUs can use NOPL. So stop
      caring about NOPs, simplify things and get on with life.
      
      [ The problem seems to be that some uarchs can only decode NOPL on a
      single front-end port while others have severe decode penalties for
      excessive prefixes. All modern uarchs can handle both, except Atom,
      which has prefix penalties. ]
      
      [ Also, much doubt you can actually measure any of this on normal
      workloads. ]
      
      After this, FEATURE_NOPL is unused except for required-features for
      x86_64. FEATURE_K8 is only used for PTI.
      
       [ bp: Kernel build measurements showed ~0.3s slowdown on Sandybridge
         which is hardly a slowdown. Get rid of X86_FEATURE_K7, while at it. ]
      Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
      Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
      Acked-by: Alexei Starovoitov <alexei.starovoitov@gmail.com> # bpf
      Acked-by: default avatarLinus Torvalds <torvalds@linuxfoundation.org>
      Link: https://lkml.kernel.org/r/20210312115749.065275711@infradead.org
      a89dfde3
  2. 06 Mar, 2021 5 commits
  3. 05 Mar, 2021 33 commits