On Sun, 27 Sep 2015 13:48:21 +0300 "Michael S. Tsirkin" <m...@redhat.com> wrote:
> 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? I'm not sure about other targets I've CCed interested parties. > > Also - does the issue only affect hotplugged memory? Potentially it affects -numa memdev=foo, but however I've tried I wasn't able to reproduce. We could do it as separate workaround later if it would affect someone and virtio is not fixed to handle split buffers by that time. > Can't the patch be local to pc-dimm (except maybe the > backwards compatibility thing)? I think decision about using gaps and its size should be done by board and not generic pc-dimm. > > 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? 1 byte should be also enough, since effectively it would kick alignment adjustment. The reason why I've picked 2Mb is that QEMU ram allocator allocates 2Mb granularity. > > > @@ -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
