On Tue, Sep 19, 2023 at 9:53 AM Ani Sinha <anisi...@redhat.com> wrote: > > On Tue, Sep 19, 2023 at 9:20 AM Ani Sinha <anisi...@redhat.com> wrote: > > > > On Mon, Sep 18, 2023 at 9:28 PM David Hildenbrand <da...@redhat.com> wrote: > > > > > > On 18.09.23 17:56, Ani Sinha wrote: > > > > On Mon, Sep 18, 2023 at 8:59 PM David Hildenbrand <da...@redhat.com> > > > > wrote: > > > >> > > > >> On 18.09.23 17:22, Ani Sinha wrote: > > > >>> On Mon, Sep 18, 2023 at 7:25 PM Ani Sinha <anisi...@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 > > I dpn't know if we always need to do this but this code adds 1 GiB per > slot for device memory : > > if (pcmc->enforce_aligned_dimm) { > /* size device region assuming 1G page max alignment per slot */ > size += (1 * GiB) * machine->ram_slots; > } > > For a 32-bit machine that is a lot of memory consumed in just alignment.
Let's look at an example when we get rid of all alignment stuff. $ ./qemu-system-i386 -machine pc-i440fx-8.2 -m 512M,slots=1,maxmem=1G above 4G start: 0x100000000,above 4G size: 0x0 qemu-system-i386: Address space limit 0xffffffff < 0x11ffffffe phys-bits too low (32) So basically, above_4g_start = 4GiB. size = 0. Then it is adding the device memory which is 1GiB - 0.5 GiB = 0.5 GiB. So the 0x11ffffffe is exactly 4.5 GiB. Anything above 4 GiB is beyond 32 bits.