kqemu+amd64: fpudna in kernel mode
jkim at FreeBSD.org
Wed Apr 11 17:22:15 UTC 2007
On Wednesday 11 April 2007 11:22 am, Andriy Gapon wrote:
> I get swarms of messages "fpudna in kernel mode" in system log when
> I run qemu with kqemu on FreeBSD 6.2 amd64 host with Windows XP
> 32-bit guest. I noticed that someone reported this problem a while
This happens because we do not allow FP instructions in kernel mode as
the error message suggested. Executing FP instructions in kernel
mode requires expensive save/restore cycles for FP states.
> There is no harm done, but the messages are annoying and they might
> be indicative of some bigger issue.
> Note that I am running qemu like follows:
> $ qemu-system-x86_64 ... -m 512 -net tap -net nic -localtime
> there is no -kernel-kqemu option and "info kqemu" in qemu monitor
> says that it is enabled for user code.
-kernel-kqemu option does not work for FreeBSD and it is very
experimental feature for Linux x86-64. Since KQEMU is release under
GPL recently, it can be fixed if someone's motivated enough,
> As I understand "fpudna" means "FPU device not available" and the
> message comes from here:
> on T_DNA ("device not avaialble") _kernel_ fault.
You can ignore the complaints for now until we come up with better FP
handling in kernel.
> BTW, not complaining about the following, but I think I should
> report it. When I use -kernel-kqemu option I get random crashes of
> the guest XP (BSOD) with diagnostics like the following (they
> Looks like all three are caused by some sort of memory corruption
> or driver misbehavior according to the following:
Windows guest is not supported by full virtualization mode, AFAIK.
BTW, it doesn't give you much performance gain as you may think:
'Best performances are achieved with Linux 2.4 kernels. Linux 2.6
works but the performance gains are small.'
Even if we make it work with FreeBSD, I would expect similar results.
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