Re: [PATCH] hw/i386/pc: fix max_used_gpa for 32-bit systems

[Ani Sinha]

On Mon, Sep 18, 2023 at 9:28 PM David Hildenbrand <david@redhat.com> wrote:
>
> On 18.09.23 17:56, Ani Sinha wrote:
> > On Mon, Sep 18, 2023 at 8:59 PM David Hildenbrand <david@redhat.com> wrote:
> >>
> >> On 18.09.23 17:22, Ani Sinha wrote:
> >>> On Mon, Sep 18, 2023 at 7:25 PM Ani Sinha <anisinha@redhat.com> wrote:
> >>>>
> >>>> 32-bit systems do not have a reserved memory for hole64 but they may 
> >>>> have a
> >>>> reserved memory space for memory hotplug. Since, hole64 starts after the
> >>>> reserved hotplug memory, the unaligned hole64 start address gives us the
> >>>> end address for this memory hotplug region that the processor may use.
> >>>> Fix this. This ensures that the physical address space bound checking 
> >>>> works
> >>>> correctly for 32-bit systems as well.
> >>>
> >>> This patch breaks some unit tests. I am not sure why it did not catch
> >>> it when I tested it before sending.
> >>> Will have to resend after fixing the tests.
> >>
> >> Probably because they supply more memory than the system can actually
> >> handle? (e.g., -m 4g on 32bit)?
> >
> > cxl tests are failing for example.
> >
> > $ ./qemu-system-i386 -display none -machine q35,cxl=on
> > qemu-system-i386: Address space limit 0xffffffff < 0x1000fffff
> > phys-bits too low (32)

also another thing is:

./qemu-system-i386 -machine pc -m 128
works but ...

$ ./qemu-system-i386 -machine pc -m 128,slots=3,maxmem=1G
qemu-system-i386: Address space limit 0xffffffff < 0x1f7ffffff
phys-bits too low (32)

or

$ ./qemu-system-i386 -machine pc-i440fx-8.2 -accel kvm -m 128,slots=3,maxmem=1G
qemu-system-i386: Address space limit 0xffffffff < 0x1f7ffffff
phys-bits too low (32)

but of course after the compat knob older pc machines work fine using
the old logic :

$ ./qemu-system-i386 -machine pc-i440fx-8.1 -accel kvm -m 128,slots=3,maxmem=1G
VNC server running on ::1:5900
^Cqemu-system-i386: terminating on signal 2




>
> CXL with 32bit CPUs ... it might be reasonably to just disable such
> tests. Certainly does not exist in real HW ... :)
>
> --
> Cheers,
>
> David / dhildenb
>