Re: qemu 6.1.0 - i386 <= 2GB?

[Frans de Boer]

On 29/11/2021 10:13, Frans de Boer wrote:

> On
>       29/11/2021 09:36, Narcis Garcia wrote: 
> > El 29/11/21 a les 9:33, Frans de Boer ha
> >         escrit: 
> > > On 29/11/2021 08:46, Narcis Garcia
> > >           wrote: 
> > > > El 28/11/21 a les 19:42, Frans de Boer
> > > >             ha escrit: 
> > > > > 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. 
> > > > >               
> > > > >             
> > > >             
> > > >             Are you sure you're using Linux [64-bit] kernel? 
> > > >             If not (32-bit), sure you're using PAE enabled Linux kernel.
> > > >             
> > > >             
> > > >           
> > >           Yes, I am sure that my system is using a 64-bit version of
> > >           Tumbleweed. 
> > >           Of course, the client in the VM is 32-bit. 
> > >           A 64-bit client (windows/linux) has no problem. 
> > >           
> > >           I will download another 32-bit iso and check if that makes a
> > >           difference. 
> > >           
> > >           --- Frans. 
> > >           
> > >         
> >         
> >         Please, copy here the complete syntax of your VM launch, and try
> >         with a guest like the one I've tried with PAE support (ubuntu
> >         18.04 i386) 
> >       
>       I just changed the '-machine type=q35,accel=kvm' into '-machine
>       type=pc' and now I have 3GB available. Probably any PAE setting in
>       the kernel is not set yet. 
>       
>       Strange, since q35 systems should be able to address upto at least
>       8GB and support upto 36-bit address space using PAE. 
>       
>       It seems that the culprit is the machine setting in combination
>       with not using PAE. I check this further today. 
>       
>       -- Frans 
>       
>     
    PAE was indeed not enabled because high memory was
      still on 4GB, hence the default kernel limit of 3GB.
      Now, the specified amount of memory is allocated and even with
      -machine type=q35, I can allocate almost 3GB. I can not allocate
      more memory for a single process due to the 3GB/1GB limit as
      imposed by the kernel.
      
      --- Frans.