1. 18 Jun, 2020 2 commits
    • Greg Kroah-Hartman's avatar
      Linux 5.7.4 · 901e2c6c
      Greg Kroah-Hartman authored
      901e2c6c
    • Thomas Gleixner's avatar
      lib/vdso: Provide sanity check for cycles (again) · 72b01e01
      Thomas Gleixner authored
      commit 72ce7780 upstream.
      
      The original x86 VDSO implementation checked for the validity of the clock
      source read by testing whether the returned signed cycles value is less
      than zero. This check was also used by the vdso read function to signal
      that the current selected clocksource is not VDSO capable.
      
      During the rework of the VDSO code the check was removed and replaced with
      a check for the clocksource mode being != NONE.
      
      This turned out to be a mistake because the check is necessary for paravirt
      and hyperv clock sources. The reason is that these clock sources have their
      own internal sequence counter to validate the clocksource at the point of
      reading it. This is necessary because the hypervisor can invalidate the
      clocksource asynchronously so a check during the VDSO data update is not
      sufficient. Having a separate indicator for the validity is slower than
      just validating the cycles value. The check for it being negative turned
      out to be the fastest implementation and safe as it would require an uptime
      of ~73 years with a 4GHz counter frequency to result in a false positive.
      
      Add an optional function to validate the cycles with a default
      implementation which allows the compiler to optimize it out for
      architectures which do not require it.
      
      Fixes: 5d51bee7
      
       ("clocksource: Add common vdso clock mode storage")
      Reported-by: default avatarMiklos Szeredi <miklos@szeredi.hu>
      Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
      Tested-by: default avatarMiklos Szeredi <mszeredi@redhat.com>
      Cc: stable@vger.kernel.org
      Link: https://lkml.kernel.org/r/20200606221531.963970768@linutronix.de
      
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      72b01e01
  2. 17 Jun, 2020 38 commits