Messages in this thread | | | Subject | Re: [PATCH] x86/TSC: Use RDTSCP | From | Guenter Roeck <> | Date | Fri, 23 Nov 2018 13:03:25 -0800 |
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On 11/23/18 12:44 PM, Borislav Petkov wrote: > On Fri, Nov 23, 2018 at 12:03:07PM -0800, Guenter Roeck wrote: >> [ 0.762832] EIP: read_tsc+0x4/0x10 >> [ 0.762832] Code: 00 01 00 eb 89 90 55 89 e5 5d c3 90 90 90 90 90 90 90 90 90 90 90 55 a1 44 5a 8b c5 89 e5 5d c3 8d b6 00 00 00 00 55 89 e5 57 <0f> ae f0b > > Where does that 'b' in f0b come from? >
Good catch.
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.
Guenter
> But ok, I was able to reproduce and decode myself. So if the Code: > section is correct, qemu chokes on MFENCE. > > [ 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 f0 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 f0 mfence <-- trapping instruction > 2d: 0f 31 rdtsc > 2f: 5d pop %ebp > 30: c3 ret > 31: 8d b6 00 00 00 00 lea 0x0(%esi),%esi > 37: 55 push %ebp > 38: 89 e5 mov %esp,%ebp > 3a: 57 push %edi > 3b: 31 ff xor %edi,%edi > 3d: 56 push %esi > 3e: 53 push %ebx > 3f: 89 .byte 0x89 > > Doing this: > > asm volatile(ALTERNATIVE_2("mfence", ... > > fails too which confirms that P3 can't do MFENCE. > > I need to think about how to handle that old cruft. > > Thx for the report. >
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