[OE-core] [PATCH] qemu: use default qemu CPU definition

[Damian, Alexandru]

Hi Cristian,

Please do post comments on patch on the mailing list.

Regarding the message itself, quoted below, I am addressing your specific
concerns.
- There is no performance impact between "qemu64" and "host" CPU options.
The only thing changing is the level of private instructions that the
kernel will attempt - which should be clearly restricted to "qemu64" and
not "host" since we build Yocto for the "qemu" machine.
- I agree that there is an underlying problem in the kernel, but that is
not our primary concern, see no 1. It might be our concern if we'd build
for a specific BSP which showed the problem, but as it stands, it's KVM
folk's concern. Funny enough, they know about the problem (I tracked on
their mailing list), but they don't have a fix since it runs as it's
designed right now - that is, the faulty behavior is a result of how it
should work with the current design.

I still recommend merging this patch since it fixes the problem with the
right fix.

Cheers,
Alex

Original message:

Hi Alex,
I might be wrong, and I need more time to investigate, but I don't
agree with the fix you proposed for this issue.

What you propose is just a step back from how qemu should optimally
work, meaning exporting "-cpu host".

That's one thing.

Another thing is the described issue seems to be specific to some
kernels on the host.
For example, I checked with LaurP and AlexG and thes issue is:
- reproducible on Ubuntu 12.10 with kernel 3.5.0.27 and Fedora Core 18
with kernel 3.8.5.
- not reproducible with Ubuntu 12.04 with kernel 3.2.x (need to check
the exact details with LaurP).

This issue needs more investigation.

Regards,
Cristian



On Mon, Apr 15, 2013 at 9:58 AM, Iorga, Cristian
<cristian.iorga at intel.com>wrote:

> Hi Alex,
>
> See my comments regarding this patch at:
> https://bugzilla.yoctoproject.org/show_bug.cgi?id=3908
>
> Regards,
> Cristian
>
> -----Original Message-----
> From: openembedded-core-bounces at lists.openembedded.org [mailto:
> openembedded-core-bounces at lists.openembedded.org] On Behalf Of Alex DAMIAN
> Sent: Tuesday, April 09, 2013 5:47 PM
> To: richard.purdie at linuxfoundation.org; tom.zanussi at linux.intel.com;
> Burton, Ross; paul.eggleton at linux.intel.com;
> openembedded-core at lists.openembedded.org
> Cc: Damian, Alexandru
> Subject: [OE-core] [PATCH] qemu: use default qemu CPU definition
>
> From: Alexandru DAMIAN <alexandru.damian at intel.com>
>
> This fixes guest crashes when trying to use restricted instructions based
> on CPU description. Using default qemu CPU descriptions restrict faults on
> using restricted model-specific registers.
>
> [YOCTO #3908]
>
> Signed-off-by: Alexandru DAMIAN <alexandru.damian at intel.com>
> ---
>  scripts/runqemu          |    2 +-
>  scripts/runqemu-internal |    6 ++++--
>  2 files changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/scripts/runqemu b/scripts/runqemu index 8ed1226..43d7600
> 100755
> --- a/scripts/runqemu
> +++ b/scripts/runqemu
> @@ -261,7 +261,7 @@ if [ "x$KVM_ENABLED" = "xyes" ]; then
>          exit 1;
>      fi
>      if [ -w /dev/kvm -a -r /dev/kvm ]; then
> -        SCRIPT_QEMU_OPT="$SCRIPT_QEMU_OPT -enable-kvm -cpu host"
> +        SCRIPT_QEMU_OPT="$SCRIPT_QEMU_OPT -enable-kvm "
>          KVM_ACTIVE="yes"
>      else
>          echo "You have no rights on /dev/kvm."
> diff --git a/scripts/runqemu-internal b/scripts/runqemu-internal index
> e8191d1..a7813e5 100755
> --- a/scripts/runqemu-internal
> +++ b/scripts/runqemu-internal
> @@ -323,10 +323,11 @@ fi
>
>  if [ "$MACHINE" = "qemux86" ]; then
>      QEMU=qemu-system-i386
> +    QEMU_CPU_OPTIONS="-cpu qemu32"
>      QEMU_UI_OPTIONS="$QEMU_UI_OPTIONS -vga vmware"
>      if [ "$FSTYPE" = "ext2" -o "$FSTYPE" = "ext3" -o "$FSTYPE" = "btrfs"
> ]; then
>          KERNCMDLINE="vga=0 uvesafb.mode_option=640x480-32 root=$DROOT rw
> mem=$QEMU_MEMORY $KERNEL_NETWORK_CMD"
> -        QEMUOPTIONS="$QEMU_NETWORK_CMD $ROOTFS_OPTIONS $QEMU_UI_OPTIONS"
> +        QEMUOPTIONS="$QEMU_NETWORK_CMD $ROOTFS_OPTIONS $QEMU_CPU_OPTIONS
> $QEMU_UI_OPTIONS"
>      fi
>      if [ "$FSTYPE" = "nfs" ]; then
>          if [ "$NFS_SERVER" = "192.168.7.1" -a ! -d "$NFS_DIR" ]; then @@
> -347,10 +348,11 @@ fi
>
>  if [ "$MACHINE" = "qemux86-64" ]; then
>      QEMU=qemu-system-x86_64
> +    QEMU_CPU_OPTIONS="-cpu qemu64"
>      QEMU_UI_OPTIONS="$QEMU_UI_OPTIONS -vga vmware"
>      if [ "$FSTYPE" = "ext3" -o "$FSTYPE" = "btrfs" ]; then
>          KERNCMDLINE="vga=0 root=$DROOT rw mem=$QEMU_MEMORY
> $KERNEL_NETWORK_CMD"
> -        QEMUOPTIONS="$QEMU_NETWORK_CMD $ROOTFS_OPTIONS $QEMU_UI_OPTIONS"
> +        QEMUOPTIONS="$QEMU_NETWORK_CMD $ROOTFS_OPTIONS $QEMU_CPU_OPTIONS
> $QEMU_UI_OPTIONS"
>      fi
>      if [ "$FSTYPE" = "nfs" ]; then
>          if [ "x$ROOTFS" = "x" ]; then
> --
> 1.7.10.4
>
>
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