wila wrote:
Thanks jmattson,
You sir, make a very good point.
But would in that case it not be needed to have a parameter set for nested virtualisation guests?
You sir, make a very good point.Not necessarily. Virtualized HV would be required to run nested 64-bit guests, but no special parameters would be necessary to run nested 32-bit guests (with binary translation). Yet, even when using binary translation, the Workstation 9 VMM requires long mode. Anyway, there's no need to focus on Workstation 9 in particular. I just give it as one example of 64-bit software that runs on a 32-bit OS.
Are there other situations in which a 32 bits guest would try to use long mode ("something solaris" now starts to nag on my memory)?
Any software that installs a kernel driver has access to the supervisory instructions necessary to enter long mode.
We do not remove long mode from your virtual CPU just because you have chosen a 32-bit guest OS type. We do not remove AVX just because you have installed an OS from the nineties. We do not remove protected mode just because you have installed MS-DOS.
MS-DOS is the poster child for not deriving necessary CPU features from guest OS type. All programs running under MS-DOS have unfettered access to supervisory mode instructions, so they can actually make use of protected mode, long mode, AVX, or whatever other features may be available on the virtual CPU. Yet, MS-DOS is a 32-bit OS.
Solaris 10 is one case where this policy leads to unfortunate consequences. Solaris 10 has one installer, and the installer will install a 64-bit OS if your CPU is 64-bit capable. It doesn't give you a choice. Thus, whether you choose 32-bit Solaris 10 or 64-bit Solaris 10 as your guest OS type, the Solaris 10 installer will install a 64-bit OS if your virtual CPU is capable of 64-bit operation. An argument could be made that selecting 32-bit Solaris 10 as your guest OS *should* disable long mode. In that case, this message would be inappropriate. However, currently, the guest OS type selection has no effect on your virtual CPU's capabilities, even if the guest OS is 32-bit Solaris 10.