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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v5 2/3] pc & q35: Add new machine opt max-ram-below-4g
On Tue, Jun 17, 2014 at 10:43:29PM +0300, Michael S. Tsirkin wrote:
> On Tue, Jun 17, 2014 at 02:44:41PM -0400, Don Slutz wrote:
> > On 06/17/14 14:22, Michael S. Tsirkin wrote:
> > >On Fri, Jun 06, 2014 at 01:52:05PM -0400, Don Slutz wrote:
> > >>This is a pc & q35 only machine opt. One use is to allow for more
> > >>ram in a 32bit guest for example:
> > >>
> > >>-machine pc,max-ram-below-4g=3.75G
> > >>
> > >>If you add enough PCI devices then all mmio for them will not fit
> > >>below 4G which may not be the layout the user wanted. This allows
> > >>you to increase the below 4G address space that PCI devices can use
> > >>(aka decrease ram below 4G) and therefore in more cases not have any
> > >>mmio that is above 4G.
> > >>
> > >>For example using "-machine pc,max-ram-below-4g=2G" on the command
> > >>line will limit the amount of ram that is below 4G to 2G.
> > >I'm not sure I get it.
> > >
> > >All this only has effect if you have >4G RAM, right?
> >
> > Nope. When it takes effect includes RAM > max-ram-below-4g. I.E.
> >
> > -machine pc,max-ram-below-4g=2G -m 3G
> >
> > Will have 2G in 32bit space (below 4G) and 1G in 64bit space (above 4G).
> >
> > >Presumably you then have a 64 bit guest so why does it
> > >care about memory/MMIO being below 4G?
> >
> > It is not the guest that matters, it is all the PCI devices in use. There
> > are
> > ones (all old hardware) that only support 32bit addresses.
>
> Emulated devices? Let's just teach them to support 64 bit BARs.
> Looks like a nicer solution than asking user to make
> this decision.
>
> > When using
> > these you may need more room.
> >
> > Also pci-passthru of real hardware that is 32bit only may require this.
> > -Don Slutz
>
> Guest and host BARs are unrelated so it seems we could allow 64 bit BARs
> even when they are 32 bit on host.
>
> Though PCI Express spec requires 64 bit BARs since version 1.0,
> are there really many devices like this out there?
> Care giving examples?
> They won't well on physical systems either.
Hmm if we are using a pci to pci bridge and bar is
non prefetcheable then that limits us to 32 bit.
So I'd like to hear a bit more about the usecase,
but it's sounding kind of reasonable.
Let's go with what I suggested in 20140617185426.GC15610@xxxxxxxxxx
then:
- user sets an upper limit
- we do min(qemu limit, user limit)
probably also warn if user-supplied limit causes
1g alignment issues.
> >
> > >
> > >
> > >>Signed-off-by: Don Slutz <dslutz@xxxxxxxxxxx>
> > >>---
> > >>v5:
> > >> Re-work based on:
> > >>
> > >> https://github.com/imammedo/qemu/commits/memory-hotplug-v11
> > >>
> > >>
> > >> hw/i386/pc.c | 38 ++++++++++++++++++++++++++++++++++++++
> > >> hw/i386/pc_piix.c | 15 ++++++++++++---
> > >> hw/i386/pc_q35.c | 15 ++++++++++++---
> > >> include/hw/i386/pc.h | 3 +++
> > >> vl.c | 4 ++++
> > >> 5 files changed, 69 insertions(+), 6 deletions(-)
> > >>
> > >>diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> > >>index 7cdba10..bccb746 100644
> > >>--- a/hw/i386/pc.c
> > >>+++ b/hw/i386/pc.c
> > >>@@ -1644,11 +1644,49 @@ pc_machine_get_hotplug_memory_region_size(Object
> > >>*obj, Visitor *v, void *opaque,
> > >> visit_type_int(v, &value, name, errp);
> > >> }
> > >>+static void pc_machine_get_max_ram_below_4g(Object *obj, Visitor *v,
> > >>+ void *opaque, const char *name,
> > >>+ Error **errp)
> > >>+{
> > >>+ PCMachineState *pcms = PC_MACHINE(obj);
> > >>+ uint64_t value = pcms->max_ram_below_4g;
> > >>+
> > >>+ visit_type_size(v, &value, name, errp);
> > >>+}
> > >>+
> > >>+static void pc_machine_set_max_ram_below_4g(Object *obj, Visitor *v,
> > >>+ void *opaque, const char *name,
> > >>+ Error **errp)
> > >>+{
> > >>+ PCMachineState *pcms = PC_MACHINE(obj);
> > >>+ Error *error = NULL;
> > >>+ uint64_t value;
> > >>+
> > >>+ visit_type_size(v, &value, name, &error);
> > >>+ if (error) {
> > >>+ error_propagate(errp, error);
> > >>+ return;
> > >>+ }
> > >>+ if (value > (1ULL << 32)) {
> > >>+ error_set(&error, ERROR_CLASS_GENERIC_ERROR,
> > >>+ "Machine option 'max-ram-below-4g=%"PRIu64
> > >>+ "' expects size less then or equal to 4G", value);
> > >>+ error_propagate(errp, error);
> > >>+ return;
> > >>+ }
> > >>+
> > >>+ pcms->max_ram_below_4g = value;
> > >>+}
> > >>+
> > >> static void pc_machine_initfn(Object *obj)
> > >> {
> > >> object_property_add(obj, PC_MACHINE_MEMHP_REGION_SIZE, "int",
> > >> pc_machine_get_hotplug_memory_region_size,
> > >> NULL, NULL, NULL, NULL);
> > >>+ object_property_add(obj, PC_MACHINE_MAX_RAM_BELOW_4G, "size",
> > >>+ pc_machine_get_max_ram_below_4g,
> > >>+ pc_machine_set_max_ram_below_4g,
> > >>+ NULL, NULL, NULL);
> > >> }
> > >> static void pc_machine_class_init(ObjectClass *oc, void *data)
> > >>diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
> > >>index 40f6eaf..25f4727 100644
> > >>--- a/hw/i386/pc_piix.c
> > >>+++ b/hw/i386/pc_piix.c
> > >>@@ -98,6 +98,13 @@ static void pc_init1(MachineState *machine,
> > >> DeviceState *icc_bridge;
> > >> FWCfgState *fw_cfg = NULL;
> > >> PcGuestInfo *guest_info;
> > >>+ Object *mo = qdev_get_machine();
> > >>+ PCMachineState *pcms = PC_MACHINE(mo);
> > >>+ ram_addr_t lowmem = 0xe0000000;
> > >>+
> > >>+ if (pcms && pcms->max_ram_below_4g) {
> > >>+ lowmem = pcms->max_ram_below_4g;
> > >>+ }
> > >> /* Check whether RAM fits below 4G (leaving 1/2 GByte for IO
> > >> memory).
> > >> * If it doesn't, we need to split it in chunks below and above 4G.
> > >>@@ -106,8 +113,10 @@ static void pc_init1(MachineState *machine,
> > >> * For old machine types, use whatever split we used historically
> > >> to avoid
> > >> * breaking migration.
> > >> */
> > >>- if (machine->ram_size >= 0xe0000000) {
> > >>- ram_addr_t lowmem = gigabyte_align ? 0xc0000000 : 0xe0000000;
> > >>+ if (machine->ram_size >= lowmem) {
> > >>+ if (!(pcms && pcms->max_ram_below_4g) && gigabyte_align) {
> > >>+ lowmem = 0xc0000000;
> > >>+ }
> > >> above_4g_mem_size = machine->ram_size - lowmem;
> > >> below_4g_mem_size = lowmem;
> > >> } else {
> > >>@@ -122,7 +131,7 @@ static void pc_init1(MachineState *machine,
> > >> }
> > >> icc_bridge = qdev_create(NULL, TYPE_ICC_BRIDGE);
> > >>- object_property_add_child(qdev_get_machine(), "icc-bridge",
> > >>+ object_property_add_child(mo, "icc-bridge",
> > >> OBJECT(icc_bridge), NULL);
> > >> pc_cpus_init(machine->cpu_model, icc_bridge);
> > >>diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
> > >>index e28ce40..155cdf1 100644
> > >>--- a/hw/i386/pc_q35.c
> > >>+++ b/hw/i386/pc_q35.c
> > >>@@ -85,6 +85,13 @@ static void pc_q35_init(MachineState *machine)
> > >> PCIDevice *ahci;
> > >> DeviceState *icc_bridge;
> > >> PcGuestInfo *guest_info;
> > >>+ Object *mo = qdev_get_machine();
> > >>+ PCMachineState *pcms = PC_MACHINE(mo);
> > >>+ ram_addr_t lowmem = 0xb0000000;
> > >>+
> > >>+ if (pcms && pcms->max_ram_below_4g) {
> > >>+ lowmem = pcms->max_ram_below_4g;
> > >>+ }
> > >> /* Check whether RAM fits below 4G (leaving 1/2 GByte for IO memory
> > >> * and 256 Mbytes for PCI Express Enhanced Configuration Access
> > >> Mapping
> > >>@@ -95,8 +102,10 @@ static void pc_q35_init(MachineState *machine)
> > >> * For old machine types, use whatever split we used historically
> > >> to avoid
> > >> * breaking migration.
> > >> */
> > >>- if (machine->ram_size >= 0xb0000000) {
> > >>- ram_addr_t lowmem = gigabyte_align ? 0x80000000 : 0xb0000000;
> > >>+ if (machine->ram_size >= lowmem) {
> > >>+ if (!(pcms && pcms->max_ram_below_4g) && gigabyte_align) {
> > >>+ lowmem = 0x800000000;
> > >>+ }
> > >> above_4g_mem_size = machine->ram_size - lowmem;
> > >> below_4g_mem_size = lowmem;
> > >> } else {
> > >>@@ -111,7 +120,7 @@ static void pc_q35_init(MachineState *machine)
> > >> }
> > >> icc_bridge = qdev_create(NULL, TYPE_ICC_BRIDGE);
> > >>- object_property_add_child(qdev_get_machine(), "icc-bridge",
> > >>+ object_property_add_child(mo, "icc-bridge",
> > >> OBJECT(icc_bridge), NULL);
> > >> pc_cpus_init(machine->cpu_model, icc_bridge);
> > >>diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
> > >>index 19530bd..2d8b562 100644
> > >>--- a/include/hw/i386/pc.h
> > >>+++ b/include/hw/i386/pc.h
> > >>@@ -32,10 +32,13 @@ struct PCMachineState {
> > >> MemoryRegion hotplug_memory;
> > >> HotplugHandler *acpi_dev;
> > >>+
> > >>+ uint64_t max_ram_below_4g;
> > >> };
> > >> #define PC_MACHINE_ACPI_DEVICE_PROP "acpi-device"
> > >> #define PC_MACHINE_MEMHP_REGION_SIZE "hotplug-memory-region-size"
> > >>+#define PC_MACHINE_MAX_RAM_BELOW_4G "max-ram-below-4g"
> > >> /**
> > >> * PCMachineClass:
> > >>diff --git a/vl.c b/vl.c
> > >>index 5e77a27..cffb9c5 100644
> > >>--- a/vl.c
> > >>+++ b/vl.c
> > >>@@ -382,6 +382,10 @@ static QemuOptsList qemu_machine_opts = {
> > >> .name = "kvm-type",
> > >> .type = QEMU_OPT_STRING,
> > >> .help = "Specifies the KVM virtualization mode (HV, PR)",
> > >>+ },{
> > >>+ .name = PC_MACHINE_MAX_RAM_BELOW_4G,
> > >>+ .type = QEMU_OPT_SIZE,
> > >>+ .help = "maximum ram below the 4G boundary (32bit boundary)",
> > >> },
> > >> { /* End of list */ }
> > >> },
> > >>--
> > >>1.8.4
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