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Linux Will End Up Disabling x86 PTI For AMD Processors - Update: Now Disabled

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  • Linux Will End Up Disabling x86 PTI For AMD Processors - Update: Now Disabled

    Phoronix: Initial Benchmarks Of The Performance Impact Resulting From Linux's x86 Security Changes

    Over the past day you've likely heard lots of hysteria about a yet-to-be-fully-disclosed vulnerability that appears to affect at least several generations of Intel CPUs and affects not only Linux but also Windows and macOS. The Intel CPU issue comes down to leaking information about the kernel memory to user-space, but the full scope isn't public yet until the bug's embargo, but it's expected to be a doozy in the data center / cloud deployments. Due to the amount of interest in this issue, here are benchmarks of a patched kernel showing the performance impact of the page table isolation patches.

    http://www.phoronix.com/vr.php?view=25767

  • #2
    Thanks Michael! As far as I know phoronix is the first news site on the web to provide benchmarks on this. Much appreciated!

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    • #3
      Linked these benchmarks on [H] as there is a good discussion on this at the moment.
      i was going to setup a simulation to push this on a ryzen with 4.14 and the latest git

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      • #4
        As of now, this vulnerability doesn't appear to affect AMD CPUs.
        Hm, so does this might affect AMD CPUs in future or something?

        Honestly didn't followed linux news recently, is this Intel-only issue or?

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        • #5
          Originally posted by dungeon View Post

          Is this Intel-only issue or?
          Apparently so: https://lkml.org/lkml/2017/12/27/2

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          • #6
            Intel only but the Linux kernel patch is not taking the risk and is gimping all x86 until further notice

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            • #7
              Nope, amd sent out a patch to disable the workaround for its cpu.
              Funny fact: the most recent Intel cpu which is guaranteed not to have this bug (as it lacks speculative execution) is the original Pentium

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              • #8
                So...

                Does it affect gaming performance?

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                • #9
                  Miscapitalization

                  NVme

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                  • #10
                    This is the discussion of the linux fix

                    https://lkml.org/lkml/2017/12/27/2

                    Code:
                    +   if (c->x86_vendor != X86_VENDOR_AMD)
                    +        setup_force_cpu_bug(X86_BUG_CPU_INSECURE);

                    --edit--
                    This is the actual commit to kernel.git
                    https://git.kernel.org/pub/scm/linux...f04e3c47d998bd

                    Code:
                    +    /* Assume for now that ALL x86 CPUs are insecure */
                    +    setup_force_cpu_bug(X86_BUG_CPU_INSECURE);
                    The proposed commit targeted non-AMD, the actual commit err'ed on the safe side until it is confirmed it doesn't affect AMD.


                    This was 10days ago. Nothing accepted to re-enable on amd

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