linux-kernel - Re: [PATCH] x86/TSC: Use RDTSCP

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Message-ID: <20181123210739.GO30697@zn.tnic>
Date:   Fri, 23 Nov 2018 22:07:39 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        John Stultz <john.stultz@...aro.org>,
        Thomas Lendacky <Thomas.Lendacky@....com>
Subject: Re: [PATCH] x86/TSC: Use RDTSCP

On Fri, Nov 23, 2018 at 01:03:25PM -0800, Guenter Roeck wrote:
> It is a cut off screen log. x86 boots change xterm configuration from
> wrap to non-wrap, and I did a cut-and-paste instead of copying the log
> to a file. Sorry for that.

No worries.

It was a head-scratcher though because look what it decodes to with the
'b':

[ 0.854209] Code: 90 90 90 90 90 90 90 a1 84 37 11 cd c3 8d b4 26 00 00 00 00 8d 76 00 c3 8d b4 26 00 00 00 00 8d b4 26 00 00 00 00 90 55 89 e5 <0f> ae f0b 0f 31 5d c3 8d b6 00 00 00 00 55 89 e5 57 31 ff 56 53 89
All code
========
   0:   90                      nop
   1:   90                      nop
   2:   90                      nop
   3:   90                      nop
   4:   90                      nop
   5:   90                      nop
   6:   90                      nop
   7:   a1 84 37 11 cd          mov    0xcd113784,%eax
   c:   c3                      ret
   d:   8d b4 26 00 00 00 00    lea    0x0(%esi,%eiz,1),%esi
  14:   8d 76 00                lea    0x0(%esi),%esi
  17:   c3                      ret
  18:   8d b4 26 00 00 00 00    lea    0x0(%esi,%eiz,1),%esi
  1f:   8d b4 26 00 00 00 00    lea    0x0(%esi,%eiz,1),%esi
  26:   90                      nop
  27:   55                      push   %ebp
  28:   89 e5                   mov    %esp,%ebp
  2a:*  0f ae 0b                fxrstor (%ebx)          <-- trapping instruction
  2d:   0f 31                   rdtsc
  2f:   5d                      pop    %ebp
  30:   c3                      ret

FXRSTOR?!?!?

:-)

-- 
Regards/Gruss,
    Boris.

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