Re: [PATCH v3 0/9] Parallel CPU bringup for x86_64

[Tom Lendacky]

On 12/17/21 1:11 PM, David Woodhouse wrote:
> On Fri, 2021-12-17 at 11:48 -0600, Tom Lendacky wrote:
> > On 12/16/21 6:13 PM, David Woodhouse wrote:
> > > On Thu, 2021-12-16 at 16:52 -0600, Tom Lendacky wrote:
> > > > On baremetal, I haven't seen an issue. This only seems to have a problem
> > > > with Qemu/KVM.
> > > >
> > > > With 191f08997577 I could boot without issues with and without the
> > > > no_parallel_bringup. Only after I applied e78fa57dd642 did the failure happen.
> > > >
> > > > With e78fa57dd642 I could boot 64 vCPUs pretty consistently, but when I
> > > > jumped to 128 vCPUs it failed again. When I moved the series to
> > > > df9726cb7178, then 64 vCPUs also failed pretty consistently.
> > > >
> > > > Strange thing is it is random. Sometimes (rarely) it works on the first
> > > > boot and then sometimes it doesn't, at which point it will reset and
> > > > reboot 3 or 4 times and then make it past the failure and fully boot.
> > >
> > > Hm, some of that is just artifacts of timing, I'm sure. But now I'm
> > > staring at the way that early_setup_idt() can run in parallel on all
> > > CPUs, rewriting bringup_idt_descr and loading it.
> > >
> > > To start with, let's try unlocking the trampoline_lock much later,
> > > after cpu_init_exception_handling() has loaded the real IDT.
> > >
> > > I think we can probably make secondaries load the real IDT early and
> > > never use bringup_idt_descr at all, can't we? But let's see if this
> > > makes it go away, to start with...
> >
> > This still fails. I ran with -d cpu_reset on the command line and will
> > forward the full log to you. I ran "grep "[ER]IP=" stderr.log | uniq -c"
> > and got:
> >
> >       128 EIP=00000000 EFL=00000000 [-------] CPL=0 II=0 A20=0 SMM=0 HLT=0
> >       128 EIP=0000fff0 EFL=00000002 [-------] CPL=0 II=0 A20=1 SMM=0 HLT=0
> > These are before running any of the vCPUs.
> >
> >         1 RIP=ffffffff810705c6 RFL=00000206 [-----P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
> > This is where vCPU0 is at the time of the reset. This address tends to
> > be different all the time and so I think it is just where it happens to
> > be when the reset occurs and isn't contributing to the reset.
>
> I note that one is in native_write_msr() though. I wonder what it's writing?
>
> Do you have console output (perhaps with earlyprintk=ttyS0) to go with this?

Yes, but it's not really much help...

[    0.146318] Freeing SMP alternatives memory: 36K
[    0.249121] smpboot: CPU0: AMD EPYC Processor (family: 0x17, model: 0x1, stepping: 0x2)
[    0.249291] Performance Events: AMD PMU driver.
[    0.249771] ... version:                0
[    0.250170] ... bit width:              48
[    0.250258] ... generic registers:      4
[    0.250662] ... value mask:             0000ffffffffffff
[    0.251258] ... max period:             00007fffffffffff
[    0.251790] ... fixed-purpose events:   0
[    0.252258] ... event mask:             000000000000000f
[    0.252972] rcu: Hierarchical SRCU implementation.
[    0.255797] smp: Bringing up secondary CPUs ...
[    0.256372] x86: Booting SMP configuration:
SecCoreStartupWithStack(0xFFFCC000, 0x820000)
Register PPI Notify: DCD0BE23-9586-40F4-B643-06522CED4EDE
Install PPI: 8C8CE578-8A3D-4F1C-9935-896185C32DD3
Install PPI: 5473C07A-3DCB-4DCA-BD6F-1E9689E7349A
The 0th FV start address is 0x00000820000, size is 0x000E0000, handle is 0x820000

There's no WARN or PANIC, just a reset. I can look to try and capture some
KVM trace data if that would help. If so, let me know what events you'd
like captured.

>

> > CPU Reset (CPU 23)
> > EIP=0000fff0 EFL=00000002 [-------] CPL=0 II=0 A20=1 SMM=0 HLT=0
>
> This one we suspect. Is this what a triple-fault would look like? Not
> if it's *already* at f000:fff0, surely?

Good question. The APM doesn't really document it. I'll see if I can find
some h/w folks to check with.

Thanks,
Tom

> CPU Reset (CPU 23)
> EAX=00000000 EBX=00000000 ECX=00000000 EDX=00800f12
> ESI=00000000 EDI=00000000 EBP=00000000 ESP=00000000
> EIP=0000fff0 EFL=00000002 [-------] CPL=0 II=0 A20=1 SMM=0 HLT=0
> ES =0000 00000000 0000ffff 00009300
> CS =f000 ffff0000 0000ffff 00009a00
> SS =0000 00000000 0000ffff 00009200
> DS =0000 00000000 0000ffff 00009300
> FS =0000 00000000 0000ffff 00009300
> GS =0000 00000000 0000ffff 00009300
> LDT=0000 00000000 0000ffff 00008200
> TR =0000 00000000 0000ffff 00008300
> GDT=     00000000 0000ffff
> IDT=     00000000 0000ffff
> CR0=00000010 CR2=00000000 CR3=00000000 CR4=00000000
> DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000
> DR6=00000000ffff0ff0 DR7=0000000000000400
> CCS=00000000 CCD=00000000 CCO=DYNAMIC
> EFER=0000000000000000
> FCW=037f FSW=0000 [ST=0] FTW=00 MXCSR=00001f80
> FPR0=0000000000000000 0000 FPR1=0000000000000000 0000
> FPR2=0000000000000000 0000 FPR3=0000000000000000 0000
> FPR4=0000000000000000 0000 FPR5=0000000000000000 0000
> FPR6=0000000000000000 0000 FPR7=0000000000000000 0000
> XMM00=0000000000000000 0000000000000000 XMM01=0000000000000000 0000000000000000
> XMM02=0000000000000000 0000000000000000 XMM03=0000000000000000 0000000000000000
> XMM04=0000000000000000 0000000000000000 XMM05=0000000000000000 0000000000000000
> XMM06=0000000000000000 0000000000000000 XMM07=0000000000000000 0000000000000000