Message ID | 20190607073721.4960-1-kraxel@redhat.com (mailing list archive) |
---|---|
State | New, archived |
Headers | show |
Series | [v2] q35: split memory at 2G | expand |
On Fri, Jun 07, 2019 at 09:37:21AM +0200, Gerd Hoffmann wrote: > Original q35 behavior was to split memory at 2.75 GB, leaving space for > the mmconfig bar at 0xb000000 and pci I/O window starting at 0xc0000000. > > Note: Those machine types have been removed from the qemu codebase > meanwhile because they could not be live-migrated so there was little > value in keeping them around. > > With the effort to allow for gigabyte-alignment of guest memory that > behavior was changed: The split was moved to 2G, but only in case the > memory didn't fit below 2.75 GB. > > So today the address space between 2G and 2,75G is not used for guest > memory in typical use cases, where the guest memory is sized at a power > of two or a gigabyte number. But if you configure your guest with some > odd amount of memory (such as 2.5G) the address space is used. > This patch removes that oddity for 4.1+ machine types. The memory is > split at 2G no matter what. And that's done on the assumption that it's a good idea such that 32 guests can address it. Could you maybe add an explanation about why this is a problem? > > Signed-off-by: Gerd Hoffmann <kraxel@redhat.com> > Acked-by: Laszlo Ersek <lersek@redhat.com> > --- > include/hw/i386/pc.h | 1 + > hw/i386/pc.c | 1 + > hw/i386/pc_q35.c | 7 ++++++- > 3 files changed, 8 insertions(+), 1 deletion(-) > > diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h > index 5d5636241e34..dfe3e6104181 100644 > --- a/include/hw/i386/pc.h > +++ b/include/hw/i386/pc.h > @@ -120,6 +120,7 @@ typedef struct PCMachineClass { > > /* RAM / address space compat: */ > bool gigabyte_align; > + bool gigabyte_split; > bool has_reserved_memory; > bool enforce_aligned_dimm; > bool broken_reserved_end; > diff --git a/hw/i386/pc.c b/hw/i386/pc.c > index edc240bcbf59..3cc9432bd187 100644 > --- a/hw/i386/pc.c > +++ b/hw/i386/pc.c > @@ -2722,6 +2722,7 @@ static void pc_machine_class_init(ObjectClass *oc, void *data) > pcmc->smbios_defaults = true; > pcmc->smbios_uuid_encoded = true; > pcmc->gigabyte_align = true; > + pcmc->gigabyte_split = true; > pcmc->has_reserved_memory = true; > pcmc->kvmclock_enabled = true; > pcmc->enforce_aligned_dimm = true; > diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c > index dcddc6466200..57d06d55ef4d 100644 > --- a/hw/i386/pc_q35.c > +++ b/hw/i386/pc_q35.c > @@ -143,8 +143,10 @@ static void pc_q35_init(MachineState *machine) > * If it doesn't, we need to split it in chunks below and above 4G. > * In any case, try to make sure that guest addresses aligned at > * 1G boundaries get mapped to host addresses aligned at 1G boundaries. > + * > + * qemu 4.1+ machines: split at 2G unconditionally (gigabyte_split = true) > */ > - if (machine->ram_size >= 0xb0000000) { > + if (machine->ram_size >= 0xb0000000 || pcmc->gigabyte_split) { > lowmem = 0x80000000; > } else { > lowmem = 0xb0000000; > @@ -376,8 +378,11 @@ DEFINE_Q35_MACHINE(v4_1, "pc-q35-4.1", NULL, > > static void pc_q35_4_0_1_machine_options(MachineClass *m) > { > + PCMachineClass *pcmc = PC_MACHINE_CLASS(m); > + > pc_q35_4_1_machine_options(m); > m->alias = NULL; > + pcmc->gigabyte_split = false; > compat_props_add(m->compat_props, hw_compat_4_0_1, hw_compat_4_0_1_len); > compat_props_add(m->compat_props, pc_compat_4_0_1, pc_compat_4_0_1_len); > } > -- > 2.18.1
diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h index 5d5636241e34..dfe3e6104181 100644 --- a/include/hw/i386/pc.h +++ b/include/hw/i386/pc.h @@ -120,6 +120,7 @@ typedef struct PCMachineClass { /* RAM / address space compat: */ bool gigabyte_align; + bool gigabyte_split; bool has_reserved_memory; bool enforce_aligned_dimm; bool broken_reserved_end; diff --git a/hw/i386/pc.c b/hw/i386/pc.c index edc240bcbf59..3cc9432bd187 100644 --- a/hw/i386/pc.c +++ b/hw/i386/pc.c @@ -2722,6 +2722,7 @@ static void pc_machine_class_init(ObjectClass *oc, void *data) pcmc->smbios_defaults = true; pcmc->smbios_uuid_encoded = true; pcmc->gigabyte_align = true; + pcmc->gigabyte_split = true; pcmc->has_reserved_memory = true; pcmc->kvmclock_enabled = true; pcmc->enforce_aligned_dimm = true; diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c index dcddc6466200..57d06d55ef4d 100644 --- a/hw/i386/pc_q35.c +++ b/hw/i386/pc_q35.c @@ -143,8 +143,10 @@ static void pc_q35_init(MachineState *machine) * If it doesn't, we need to split it in chunks below and above 4G. * In any case, try to make sure that guest addresses aligned at * 1G boundaries get mapped to host addresses aligned at 1G boundaries. + * + * qemu 4.1+ machines: split at 2G unconditionally (gigabyte_split = true) */ - if (machine->ram_size >= 0xb0000000) { + if (machine->ram_size >= 0xb0000000 || pcmc->gigabyte_split) { lowmem = 0x80000000; } else { lowmem = 0xb0000000; @@ -376,8 +378,11 @@ DEFINE_Q35_MACHINE(v4_1, "pc-q35-4.1", NULL, static void pc_q35_4_0_1_machine_options(MachineClass *m) { + PCMachineClass *pcmc = PC_MACHINE_CLASS(m); + pc_q35_4_1_machine_options(m); m->alias = NULL; + pcmc->gigabyte_split = false; compat_props_add(m->compat_props, hw_compat_4_0_1, hw_compat_4_0_1_len); compat_props_add(m->compat_props, pc_compat_4_0_1, pc_compat_4_0_1_len); }