On Tue, Sep 19, 2023 at 4:08 PM Ani Sinha <[email protected]> wrote: > > 32-bit systems do not have a reserved memory for hole64 and memory hotplug is > not supported on those systems. Therefore, the maximum limit of the guest > physical address coincides with the end of "above 4G memory space" region. > Make sure that the end of "above 4G memory" is still addressible by the > guest processor with its available address bits. For example, previously this > was allowed: > > $ ./qemu-system-x86_64 -cpu pentium -m size=10G > > Now it is no longer allowed: > > $ ./qemu-system-x86_64 -cpu pentium -m size=10G > qemu-system-x86_64: Address space limit 0xffffffff < 0x2bfffffff phys-bits > too low (32) > > After calling CPUID with EAX=0x80000001, all AMD64 compliant processors > have the longmode-capable-bit turned on in the extended feature flags (bit 29) > in EDX. The absence of CPUID longmode can be used to differentiate between > 32-bit and 64-bit processors and is the recommended approach. QEMU takes this > approach elsewhere (for example, please see x86_cpu_realizefn()) and with > this change, pc_max_used_gpa() also takes the same approach to detect 32-bit > processors. > > Finally, a new compatibility flag is introduced to retain the old behavior > for pc_max_used_gpa() for macines 8.1 and older. typo - will fix in v3 ^^^^^^^^
btw, does this patch break it for processors < 32-bit? For them clearly x86ms->above_4g_mem_start = 4 * GiB; does not work. > > Suggested-by: David Hildenbrand <[email protected]> > Signed-off-by: Ani Sinha <[email protected]> > --- > hw/i386/pc.c | 17 ++++++++++++++--- > hw/i386/pc_piix.c | 4 ++++ > include/hw/i386/pc.h | 3 +++ > 3 files changed, 21 insertions(+), 3 deletions(-) > > changelog: > v2: removed memory hotplug region from max_gpa. added compat knobs. > > diff --git a/hw/i386/pc.c b/hw/i386/pc.c > index 54838c0c41..fea97ee258 100644 > --- a/hw/i386/pc.c > +++ b/hw/i386/pc.c > @@ -907,10 +907,20 @@ static uint64_t pc_get_cxl_range_end(PCMachineState > *pcms) > static hwaddr pc_max_used_gpa(PCMachineState *pcms, uint64_t pci_hole64_size) > { > X86CPU *cpu = X86_CPU(first_cpu); > + PCMachineClass *pcmc = PC_MACHINE_GET_CLASS(pcms); > > - /* 32-bit systems don't have hole64 thus return max CPU address */ > - if (cpu->phys_bits <= 32) { > - return ((hwaddr)1 << cpu->phys_bits) - 1; > + /* > + * 32-bit systems don't have hole64 and does not support > + * memory hotplug. > + */ > + if (pcmc->fixed_32bit_mem_addr_check) { > + if (!(cpu->env.features[FEAT_8000_0001_EDX] & CPUID_EXT2_LM)) { > + return pc_above_4g_end(pcms) - 1; > + } > + } else { > + if (cpu->phys_bits <= 32) { > + return ((hwaddr)1 << cpu->phys_bits) - 1; > + } > } > > return pc_pci_hole64_start() + pci_hole64_size - 1; > @@ -1867,6 +1877,7 @@ static void pc_machine_class_init(ObjectClass *oc, void > *data) > pcmc->pvh_enabled = true; > pcmc->kvmclock_create_always = true; > pcmc->resizable_acpi_blob = true; > + pcmc->fixed_32bit_mem_addr_check = true; > assert(!mc->get_hotplug_handler); > mc->get_hotplug_handler = pc_get_hotplug_handler; > mc->hotplug_allowed = pc_hotplug_allowed; > diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c > index 8321f36f97..f100a5de8b 100644 > --- a/hw/i386/pc_piix.c > +++ b/hw/i386/pc_piix.c > @@ -517,9 +517,13 @@ DEFINE_I440FX_MACHINE(v8_2, "pc-i440fx-8.2", NULL, > > static void pc_i440fx_8_1_machine_options(MachineClass *m) > { > + PCMachineClass *pcmc = PC_MACHINE_CLASS(m); > + > pc_i440fx_8_2_machine_options(m); > m->alias = NULL; > m->is_default = false; > + pcmc->fixed_32bit_mem_addr_check = false; > + > compat_props_add(m->compat_props, hw_compat_8_1, hw_compat_8_1_len); > compat_props_add(m->compat_props, pc_compat_8_1, pc_compat_8_1_len); > } > diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h > index 0fabece236..5a70d163d0 100644 > --- a/include/hw/i386/pc.h > +++ b/include/hw/i386/pc.h > @@ -129,6 +129,9 @@ struct PCMachineClass { > > /* resizable acpi blob compat */ > bool resizable_acpi_blob; > + > + /* fixed 32-bit processor address space bound check for memory */ > + bool fixed_32bit_mem_addr_check; > }; > > #define TYPE_PC_MACHINE "generic-pc-machine" > -- > 2.39.1 >
