Re: qemu 6.1.0 - i386 <= 2GB?

[Frans de Boer]

On 24/11/2021 09:42, Narcis Garcia wrote:
> El 23/11/21 a les 14:33, Frans de Boer ha escrit:
> > On 23/11/2021 11:44, Narcis Garcia wrote:
> > > El 23/11/21 a les 10:03, Frans de Boer ha escrit:
> > > > On 23/11/2021 09:27, Narcis Garcia wrote:
> > > > > Some 32-bit system can't handle more than 512 MiB of RAM, and some 
> > > > > 32-bit systems can handle up to 64 GiB.
> > > > >
> > > > > This is not related to memory assigned by Qemu to VE.
> > > > >
> > > > >
> > > > > Narcis Garcia
> > > > >
> > > > > El 22/11/21 a les 18:38, Frans de Boer ha escrit:
> > > > > > LS,
> > > > > >
> > > > > > OK, 32-bit systems can't handle more than 4GB memory. So, I 
> > > > > > specify '-m 4096' and still get only 2GB. Is this (very) old bug 
> > > > > > still not resolved or is it a feature now?
> > > > > >
> > > > > > Regards, Frans.
> > > > In theory an 32-bit processor can handle up-to 4GB of physical 
> > > > memory. However, due to limitations of some chip sets, the maximum 
> > > > amount of memory was often 512 MB or 1 GB. At that time the chip 
> > > > sets where lagging behind the processor capabilities.
> > > > With newer chip sets it became practically possible to address 4 GB 
> > > > and when using PAE, even beyond that. Although in case of the 
> > > > latter, the address space for a single process was always limited 
> > > > to 4 GB.
> > > >
> > > > So, whatever way you see it, the 2 GB limit imposed by QEMU seems 
> > > > rather arbitrary.
> > > >
> > > > --- Frans.
> > >
> > > Before talking about 64 GiB limit, I just tried 
> > > ubuntu-mate-18.04.1-desktop-i386 in a Qemu 5.2.0 VM
> > > 50 GiB assigned and guest OS detects and uses it.
> > Then, what type of CPU did you specify?
>
> I've tried now with these four modes:
> qemu-system-x86_64 -m 51200 -cpu host [intel core i5]
> qemu-system-x86_64 -m 51200 -cpu pentium2
> qemu-system-i386 -m 51200 -cpu host
> qemu-system-i386 -m 51200 -cpu pentium2
> qemu-system-i386 -m 51200 -cpu kvm32
>
> each of them detect & use 50GiB of RAM.
> Other parameters of interest:
> -vga qxl -display gtk -enable-kvm -boot d -drive 
> file=ubuntu-mate-18.04.1-desktop-i386.iso,media=cdrom,index=0
>
> * If I try with booting 64-bit OS (ubuntu-18.04-desktop-amd64) then I 
> get Linux message "This kernel requires an x86-64 CPU, but only 
> detected an i686 CPU." and it does not boot.
> * If I try with "-cpu pentium" then I get Linux message "This kernel 
> requires the following features not present on the CPU: pae cmov" and 
> it does not boot.
>
> ARE YOU SURE you're using a modern operating system?
Okay, I needed some time before I could continue.

I am building my own version of a linux system, but use OpenSuse TW 
(64-bit) as base. Updated almost every second day.
Now, when I either use ´-cpu pentium´ or ´-cpu kvm32´, I never can 
allocate more than 2 GB, no matter the -m size.
I do see that virtual memory is being increased, but the available 
memory for allocation is never more than 2GB.

So, yes the requested memory is allocated - albeit virtual -, but the 
excess above 2GB is never used.

--- Frans.