rdtscp support (was Re: bhyve guest illegal instruction)
Hi Chuck, 12 time1 = __builtin_ia32_rdtscp(); rdtscp shouldn't be used without checking that it's available via CPUID first, but as you mentioned the feature is available on the host, just hidden from the guest. This same program works on the FreeBSD 12-stable machine hosting the VM as well as another bare-metal Linux host. Poking around in the vmm code, I found /* * Hide rdtscp/ia32_tsc_aux until we know how * to deal with them. */ regs[3] &= ~AMDID_RDTSCP; break; in sys/amd64/vmm/x86.c which I _think_ is relevant because lscpu doesn't show the rdtscp flag. If this is the root cause, what would need to be done to implement this? At a quick glance, if the feature is available on the host you'd need to - expose it via CPUID - save/restore the TSC_AUX MSR, but using the VMCS MSR h/w save/restore mechanism that will have to be resurrected. (this avoids any preemption issues,even at NMI level). - set the "enable RDTSCP" VM-execution control to one in the VMCS That being said, I've heard anecdotally that rdtscp results in VM-exits on other hypervisors so there may be reason to emulate it rather than allow a pass-thru. More investigation may be required. later, Peter. ___ freebsd-virtualization@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-virtualization To unsubscribe, send any mail to "freebsd-virtualization-unsubscr...@freebsd.org"
bhyve guest illegal instruction
(apologies for the resend, this time with a Subject)
John / Peter
I'm running an application in a Linux guest under bhyve that is core
dumping because of an Illegal instruction. Running a simplified case in gdb
shows:
$ gdb -q rdtscp
Reading symbols from rdtscp...done.
(gdb) run
Starting program: /home/tuffli/rdtscp
Program received signal SIGILL, Illegal instruction.
main (argc=1, argv=0x7fffeae8) at rdtscp.c:12
12 time1 = __builtin_ia32_rdtscp();
(gdb) l
7 main(int argc, char *argv[])
8 {
9uint64_t time1, time2;
10 uint32_t dummy;
11
12 time1 = __builtin_ia32_rdtscp();
13 usleep(1000);
14 time2 = __builtin_ia32_rdtscp();
15
16 printf("time delta %lu\n", time2 - time1);
17
18 return (EXIT_SUCCESS);
19 }
This same program works on the FreeBSD 12-stable machine hosting the VM as
well as another bare-metal Linux host. Poking around in the vmm code, I
found
/*
* Hide rdtscp/ia32_tsc_aux until we know how
* to deal with them.
*/
regs[3] &= ~AMDID_RDTSCP;
break;
in sys/amd64/vmm/x86.c which I _think_ is relevant because lscpu doesn't
show the rdtscp flag. If this is the root cause, what would need to be done
to implement this?
--chuck
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[no subject]
John / Peter
I'm running an application in a Linux guest under bhyve that is core
dumping because of an Illegal instruction. Running a simplified case in gdb
shows:
$ gdb -q rdtscp
Reading symbols from rdtscp...done.
(gdb) run
Starting program: /home/tuffli/rdtscp
Program received signal SIGILL, Illegal instruction.
main (argc=1, argv=0x7fffeae8) at rdtscp.c:12
12 time1 = __builtin_ia32_rdtscp();
(gdb) l
7 main(int argc, char *argv[])
8 {
9uint64_t time1, time2;
10 uint32_t dummy;
11
12 time1 = __builtin_ia32_rdtscp();
13 usleep(1000);
14 time2 = __builtin_ia32_rdtscp();
15
16 printf("time delta %lu\n", time2 - time1);
17
18 return (EXIT_SUCCESS);
19 }
This same program works on the FreeBSD 12-stable machine hosting the VM as
well as another bare-metal Linux host. Poking around in the vmm code, I
found
/*
* Hide rdtscp/ia32_tsc_aux until we know how
* to deal with them.
*/
regs[3] &= ~AMDID_RDTSCP;
break;
in sys/amd64/vmm/x86.c which I _think_ is relevant because lscpu doesn't
show the rdtscp flag. If this is the root cause, what would need to be done
to implement this?
--chuck
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