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DescriptionEduardo Habkost
2012-04-19 20:36:16 UTC
Cloning the bug specifically for the "rdtscp" flag. The flag is defined on the SandyBridge and Opteron CPU models, but not supported by the kernel. "-cpu <model>,check" and "-cpu <model>,enforce" should have detected it, but it didn't.
So, we have to:
1) Either remove the flag from the model definitions, or add rdtscp support to the KVM module
2) Make "-cpu <model>,check" actually detect the missing flag (bug 692374)
+++ This bug was initially created as a clone of Bug #813132 +++
Description of problem:
can find "sep" flag in /usr/libexec/qemu-kvm -cpu ?dump and cann't find it /proc/cpuinof on host. but haven't any warning message when booting guest.
BTW, "sep" isn't exposted to guest.
"rdtscp" flag is defined in dump and /proc/cpuinfo on host but it isn't exposted to guest.
Version-Release number of selected component (if applicable):
# uname -r
2.6.32-259.el6.x86_64
#rpm -qa|grep qemu
qemu-kvm-0.12.1.2-2.270.el6.x86_64
How reproducible:
always
Steps to Reproduce:
1./usr/libexec/qemu-kvm -M rhel6.3.0 -cpu SandyBridge --enable-kvm -m 4G -smp
40,sockets=2,cores=10,threads=2,maxcpus=41 -name rhel6.3 -uuid
ddcbfb49-3411-1701-3c36-6bdbc00bedbb -rtc base=utc,clock=host,driftfix=slew
-boot c -drive
file=/mnt/rhel6.3.raw,format=raw,if=none,id=disk0,cache=none,werror=stop,rerror=stop
-device virtio-scsi-pci,id=disk0 -device
scsi-hd,drive=disk0,scsi-id=0,lun=0,bootindex=1 -netdev tap,id=hostnet1 -device
virtio-net-pci,netdev=hostnet1,id=net1,mac=86:12:50:a4:32:72 -spice
port=5911,disable-ticketing -vga qxl -device sga -chardev
socket,id=serial0,path=/var/test1,server,nowait -device
isa-serial,chardev=serial0 -balloon virtio -monitor
unix:/tmp/monitor1,server,nowait -monitor stdio
2. find "sep" flag from dump
3. find "rdtscp" flag from dump and cpuinfo on host
4. check above two flags in guest
Actual results:
1. can find "sep" from dump, no any warning message when booting guest.
2. can find "rdtscp" from dump and cpuinfo on host,but cann't find it from guest
Expected results:
qemu should have warning message because "sep" flag isn't defined in host.
rdtscp should expose to guest.
Additional info:
This is the expected result. We have followed the first approach mentioned on comment #0 -- the rdtscp flag was removed from all CPU models to reflect reality because it is not supported by the RHEL-6 kernel.
(In reply to comment #3)
> This is the expected result. We have followed the first approach mentioned
> on comment #0 -- the rdtscp flag was removed from all CPU models to reflect
> reality because it is not supported by the RHEL-6 kernel.
I had a little confused.
1. expected result "rdtscp should expose to guest" in comment #0
2. can find "rdtscp" from cpuinfo on host, indicate rhel6 kernel support this flag(this is my understand).
3. If remove this flag from all CPU models, It should be removed from dump,right?
(In reply to comment #4)
> (In reply to comment #3)
> > This is the expected result. We have followed the first approach mentioned
> > on comment #0 -- the rdtscp flag was removed from all CPU models to reflect
> > reality because it is not supported by the RHEL-6 kernel.
>
> I had a little confused.
>
> 1. expected result "rdtscp should expose to guest" in comment #0
It should be exposed if it's set on the CPU models. There were two possible solutions: add rdtscp support to the kernel, or remove the flag from the CPU models to reflect what's actually being exposed to guests when using RHEL-6.3 qemu-kvm. We chose the second approach.
> 2. can find "rdtscp" from cpuinfo on host, indicate rhel6 kernel support
> this flag(this is my understand).
No, the KVM kernel code has to support it too, and the RHEL-6 KVM kernel code doesn't support exposing rdtscp to guests. That's what makes the rdtscp flag not appear to the guest (as the flags are filtered according to the host CPU + host kernel capabilities[1]).
[1] The filtering should be reported by -cpu check/enforce, and the existing bug on -cpu check/enforce is being tracked at bug 692374.
> 3. If remove this flag from all CPU models, It should be removed from
> dump,right?
It should have been removed from the CPU model dump ("-cpu ?dump"), but -cpu ?dump doesn't exist anymore. The flag removal is only visible by looking at the CPU model definitions in the C code at qemu-kvm/target-i386/cpuid.c.
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory, and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
http://rhn.redhat.com/errata/RHBA-2013-0527.html