On Fri, Sep 25, 2015 at 03:53:12PM +0200, Igor Mammedov wrote: > mapping DIMMs non contiguously allows to workaround > virtio bug reported earlier: > http://lists.nongnu.org/archive/html/qemu-devel/2015-08/msg00522.html > in this case guest kernel doesn't allocate buffers > that can cross DIMM boundary keeping each buffer > local to a DIMM. > > Suggested-by: Michael S. Tsirkin <m...@redhat.com> > Signed-off-by: Igor Mammedov <imamm...@redhat.com> > --- > benefit of this workaround is that no guest side > changes are required.
That's a hard requirement, I agree. > --- > hw/i386/pc.c | 4 +++- > hw/i386/pc_piix.c | 3 +++ > hw/i386/pc_q35.c | 3 +++ > include/hw/i386/pc.h | 2 ++ > 4 files changed, 11 insertions(+), 1 deletion(-) Aren't other architectures besides PC ever affected? Do they all allocate all of memory contigious in HVA space? Also - does the issue only affect hotplugged memory? Can't the patch be local to pc-dimm (except maybe the backwards compatibility thing)? > diff --git a/hw/i386/pc.c b/hw/i386/pc.c > index 91d134c..c462c4e 100644 > --- a/hw/i386/pc.c > +++ b/hw/i386/pc.c > @@ -1629,6 +1629,7 @@ static void pc_dimm_plug(HotplugHandler *hotplug_dev, > HotplugHandlerClass *hhc; > Error *local_err = NULL; > PCMachineState *pcms = PC_MACHINE(hotplug_dev); > + PCMachineClass *pcmc = PC_MACHINE_GET_CLASS(pcms); > PCDIMMDevice *dimm = PC_DIMM(dev); > PCDIMMDeviceClass *ddc = PC_DIMM_GET_CLASS(dimm); > MemoryRegion *mr = ddc->get_memory_region(dimm); > @@ -1644,7 +1645,8 @@ static void pc_dimm_plug(HotplugHandler *hotplug_dev, > goto out; > } > > - pc_dimm_memory_plug(dev, &pcms->hotplug_memory, mr, align, 0, > &local_err); > + pc_dimm_memory_plug(dev, &pcms->hotplug_memory, mr, align, > + pcmc->inter_dimm_gap, &local_err); > if (local_err) { > goto out; > } > diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c > index 3ffb05f..3165667 100644 > --- a/hw/i386/pc_piix.c > +++ b/hw/i386/pc_piix.c > @@ -457,11 +457,13 @@ static void pc_xen_hvm_init(MachineState *machine) > > static void pc_i440fx_machine_options(MachineClass *m) > { > + PCMachineClass *pcmc = PC_MACHINE_CLASS(m); > m->family = "pc_piix"; > m->desc = "Standard PC (i440FX + PIIX, 1996)"; > m->hot_add_cpu = pc_hot_add_cpu; > m->default_machine_opts = "firmware=bios-256k.bin"; > m->default_display = "std"; > + pcmc->inter_dimm_gap = PC_2MB_DIMM_GAP; > } > > static void pc_i440fx_2_5_machine_options(MachineClass *m) > @@ -482,6 +484,7 @@ static void pc_i440fx_2_4_machine_options(MachineClass *m) > m->alias = NULL; > m->is_default = 0; > pcmc->broken_reserved_end = true; > + pcmc->inter_dimm_gap = 0; > SET_MACHINE_COMPAT(m, PC_COMPAT_2_4); > } > > diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c > index 1b7d3b6..8ad6687 100644 > --- a/hw/i386/pc_q35.c > +++ b/hw/i386/pc_q35.c > @@ -360,6 +360,7 @@ static void pc_compat_1_4(MachineState *machine) > > static void pc_q35_machine_options(MachineClass *m) > { > + PCMachineClass *pcmc = PC_MACHINE_CLASS(m); > m->family = "pc_q35"; > m->desc = "Standard PC (Q35 + ICH9, 2009)"; > m->hot_add_cpu = pc_hot_add_cpu; > @@ -368,6 +369,7 @@ static void pc_q35_machine_options(MachineClass *m) > m->default_display = "std"; > m->no_floppy = 1; > m->no_tco = 0; > + pcmc->inter_dimm_gap = PC_2MB_DIMM_GAP; > } > > static void pc_q35_2_5_machine_options(MachineClass *m) > @@ -385,6 +387,7 @@ static void pc_q35_2_4_machine_options(MachineClass *m) > pc_q35_2_5_machine_options(m); > m->alias = NULL; > pcmc->broken_reserved_end = true; > + pcmc->inter_dimm_gap = 0; > SET_MACHINE_COMPAT(m, PC_COMPAT_2_4); > } > > diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h > index 6896328..dd6b34a 100644 > --- a/include/hw/i386/pc.h > +++ b/include/hw/i386/pc.h > @@ -50,6 +50,7 @@ struct PCMachineState { > #define PC_MACHINE_SMM "smm" > #define PC_MACHINE_ENFORCE_ALIGNED_DIMM "enforce-aligned-dimm" > > +#define PC_2MB_DIMM_GAP (1ULL << 21) > /** > * PCMachineClass: > * @get_hotplug_handler: pointer to parent class callback > @get_hotplug_handler Seems somewhat arbitrary. It's aligned later - so won't a 1 byte gap be enough? > @@ -60,6 +61,7 @@ struct PCMachineClass { > > /*< public >*/ > bool broken_reserved_end; > + uint64_t inter_dimm_gap; > HotplugHandler *(*get_hotplug_handler)(MachineState *machine, > DeviceState *dev); > }; > -- > 1.8.3.1