Re: port-amd64/49150: xrstor is privileged in Xen

[Jeff Rizzo <riz%NetBSD.org@localhost>]

The following reply was made to PR port-amd64/49150; it has been noted by GNATS.

From: Jeff Rizzo <riz%NetBSD.org@localhost>
To: gnats-bugs%NetBSD.org@localhost
Cc: 
Subject: Re: port-amd64/49150: xrstor is privileged in Xen
Date: Mon, 27 Oct 2014 16:09:42 -0700

 On 9/11/14 1:10 PM, David Laight wrote:
 >   
 >   ISTR this is in 'fpu' setup deecting avx??
 >   
 >   IIRC the kernel only calls xrstor instruction if one of the other
 >   registers says it is available.
 >   So xen is failing to lie....
 >   
 >   Possibly the instruction needs a 'trap detect' added and to disable avx
 >   if it faults.
 >   
 
 I've discovered another processor for which it fails:
 
 NetBSD 7.0_BETA (XEN3_DOMU.201410252300Z)
 total memory = 615 MB
 avail memory = 586 MB
 kern.module.path=/stand/amd64/7.0/modules
 mainbus0 (root)
 hypervisor0 at mainbus0: Xen version 3.4.3.amazon
 vcpu0 at hypervisor0: Intel(R) Xeon(R) CPU E5-2650 0 @ 2.00GHz, id 0x206d7
 xenbus0 at hypervisor0: Xen Virtual Bus Interface
 xencons0 at hypervisor0: Xen Virtual Console Driver
 xbd0 at xenbus0 id 2049: Xen Virtual Block Device Interface
 xbd1 at xenbus0 id 2050: Xen Virtual Block Device Interface
 xennet0 at xenbus0 id 0: Xen Virtual Network Interface
 xennet0: MAC address 22:00:0a:5b:94:c4
 balloon0 at xenbus0 id 0: Xen Balloon driver
 balloon0: current reservation: 629760 KiB
 xennet0: using RX copy mode
 boot device: xbd1
 root on xbd1a dumps on xbd1b
 balloon0: current reservation: 157440 pages => target: 157440 pages
 root file system type: ffs
 fatal privileged instruction fault in supervisor mode
 trap type 0 code 0 rip ffffffff8012e3a2 cs e030 rflags 10246 cr2 
 7f7ff781db1c ilevel 8 rsp ffffa0001c7feec8
 curlwp 0xffffa000017c4120 pid 14.1 lowest kstack 0xffffa0001c7fc2c0
 kernel: privileged instruction fault trap, code=0
 Stopped in pid 14.1 (ps) at     netbsd:xrstor+0xa:      fxsavel
 xrstor() at netbsd:xrstor+0xa
 ds          4120
 es          95c0
 fs          0
 gs          d000
 rdi         ffffa0001c7fc080
 rsi         7
 rbp         ffffa0001c7feef0
 rbx         ffffa000017c4120
 rdx         0
 rcx         0
 rax         7
 r8          3ff
 r9          7f7fffffdc50
 r10         7f7ff7c0c19a
 r11         246
 r12         ffffffff805d4600    cpu_info_primary
 r13         ffffa0001c7fc000
 r14         0
 r15         4001c8
 rip         ffffffff8012e3a2    xrstor+0xa
 cs          e030
 rflags      10246
 rsp         ffffa0001c7feec8
 ss          e02b
 netbsd:xrstor+0xa:      fxsavel
 db{0}>
 
 
 Given that these are in use on Amazon EC2 instances, I'm going to work 
 around the problem in a similar fashion for now.