Re: [Qemu-devel] [RFC PATCH 1/4] pc-dimm: add 'reserved-size' to reserve address range after the ending address

[Haozhong Zhang <haozhong.zhang@intel.com>]

On 04/06/17 11:24 +0100, Stefan Hajnoczi wrote:
> On Fri, Mar 31, 2017 at 04:41:44PM +0800, Haozhong Zhang wrote:
> > If option 'reserved-size=RSVD' is present, QEMU will reserve an
> > address range of size 'RSVD' after the ending address of pc-dimm
> > device.
> > 
> > For the following example,
> >     -object memory-backend-file,id=mem0,size=4G,...
> >     -device nvdimm,id=dimm0,memdev=mem0,reserved-size=4K,...
> 
> "reserved-size" is not a clear name.  I suggest calling the property
> "num-flush-hints" (default 0).  QEMU can calculate the actual size in
> bytes.
> 
>   -device nvdimm,num-flush-hints=1
> 
> QEMU will use one flush hint and reserve enough space (e.g. 1 page) for
> the MMIO region.
>

Each flush hint can be as small as one cache line size which is also
the size used in this patch series.

We need to calculate the size of all flush hints in pc_dimm_memory_plug(),
because when building the flush hint address structure we need to know
the address of flush hints.

IIUC, pc_dimm_memory_plug() is not specific to x86, so it's better
take a general way to get the vcpu cache line size in pc_dimm_memory_plug(),
which seemingly lacks in QEMU (though I believe it should be doable).

To make things simple, I leave the size decision to users, and check
whether it's large enough when building the flush hint address
structures in patch 4.


Haozhong

> >     -device pc-dimm,id=dimm1,...
> > if dimm0 is allocated to address N ~ N+4G, the address range of
> > dimm1 will start from N+4G+4K or higher.
> > 
> > Its current usage is to reserve spaces for flush hint addresses
> > of nvdimm devices.
> > 
> > Signed-off-by: Haozhong Zhang <haozhong.zhang@intel.com>
> > ---
> >  hw/mem/pc-dimm.c         | 48 +++++++++++++++++++++++++++++++++++++++++++++---
> >  include/hw/mem/pc-dimm.h |  2 ++
> >  2 files changed, 47 insertions(+), 3 deletions(-)
> > 
> > diff --git a/hw/mem/pc-dimm.c b/hw/mem/pc-dimm.c
> > index 9e8dab0..13dcd71 100644
> > --- a/hw/mem/pc-dimm.c
> > +++ b/hw/mem/pc-dimm.c
> > @@ -28,6 +28,7 @@
> >  #include "sysemu/kvm.h"
> >  #include "trace.h"
> >  #include "hw/virtio/vhost.h"
> > +#include "exec/address-spaces.h"
> >  
> >  typedef struct pc_dimms_capacity {
> >       uint64_t size;
> > @@ -44,7 +45,12 @@ void pc_dimm_memory_plug(DeviceState *dev, MemoryHotplugState *hpms,
> >      MemoryRegion *vmstate_mr = ddc->get_vmstate_memory_region(dimm);
> >      Error *local_err = NULL;
> >      uint64_t existing_dimms_capacity = 0;
> > -    uint64_t addr;
> > +    uint64_t addr, size = memory_region_size(mr);
> > +
> > +    size += object_property_get_int(OBJECT(dimm), PC_DIMM_RSVD_PROP, &local_err);
> > +    if (local_err) {
> > +        goto out;
> > +    }
> >  
> >      addr = object_property_get_int(OBJECT(dimm), PC_DIMM_ADDR_PROP, &local_err);
> >      if (local_err) {
> > @@ -54,7 +60,7 @@ void pc_dimm_memory_plug(DeviceState *dev, MemoryHotplugState *hpms,
> >      addr = pc_dimm_get_free_addr(hpms->base,
> >                                   memory_region_size(&hpms->mr),
> >                                   !addr ? NULL : &addr, align,
> > -                                 memory_region_size(mr), &local_err);
> > +                                 size, &local_err);
> >      if (local_err) {
> >          goto out;
> >      }
> > @@ -64,7 +70,7 @@ void pc_dimm_memory_plug(DeviceState *dev, MemoryHotplugState *hpms,
> >          goto out;
> >      }
> >  
> > -    if (existing_dimms_capacity + memory_region_size(mr) >
> > +    if (existing_dimms_capacity + size >
> >          machine->maxram_size - machine->ram_size) {
> >          error_setg(&local_err, "not enough space, currently 0x%" PRIx64
> >                     " in use of total hot pluggable 0x" RAM_ADDR_FMT,
> > @@ -315,6 +321,9 @@ uint64_t pc_dimm_get_free_addr(uint64_t address_space_start,
> >          PCDIMMDevice *dimm = item->data;
> >          uint64_t dimm_size = object_property_get_int(OBJECT(dimm),
> >                                                       PC_DIMM_SIZE_PROP,
> > +                                                     errp) +
> > +                             object_property_get_int(OBJECT(dimm),
> > +                                                     PC_DIMM_RSVD_PROP,
> >                                                       errp);
> >          if (errp && *errp) {
> >              goto out;
> > @@ -382,6 +391,37 @@ static void pc_dimm_check_memdev_is_busy(Object *obj, const char *name,
> >      error_propagate(errp, local_err);
> >  }
> >  
> > +static void pc_dimm_get_reserved_size(Object *obj, Visitor *v, const char *name,
> > +                                      void *opaque, Error **errp)
> > +{
> > +    PCDIMMDevice *dimm = PC_DIMM(obj);
> > +    uint64_t value = dimm->reserved_size;
> > +
> > +    visit_type_size(v, name, &value, errp);
> > +}
> > +
> > +static void pc_dimm_set_reserved_size(Object *obj, Visitor *v, const char *name,
> > +                                      void *opaque, Error **errp)
> > +{
> > +    PCDIMMDevice *dimm = PC_DIMM(obj);
> > +    Error *local_err = NULL;
> > +    uint64_t value;
> > +
> > +    if (dimm->reserved_size) {
> > +        error_setg(&local_err, "cannot change 'reserved-size'");
> > +        goto out;
> > +    }
> > +
> > +    visit_type_size(v, name, &value, &local_err);
> > +    if (local_err) {
> > +        goto out;
> > +    }
> > +    dimm->reserved_size = value;
> > +
> > + out:
> > +    error_propagate(errp, local_err);
> > +}
> > +
> >  static void pc_dimm_init(Object *obj)
> >  {
> >      PCDIMMDevice *dimm = PC_DIMM(obj);
> > @@ -393,6 +433,8 @@ static void pc_dimm_init(Object *obj)
> >                               pc_dimm_check_memdev_is_busy,
> >                               OBJ_PROP_LINK_UNREF_ON_RELEASE,
> >                               &error_abort);
> > +    object_property_add(obj, PC_DIMM_RSVD_PROP, "int", pc_dimm_get_reserved_size,
> > +                        pc_dimm_set_reserved_size, NULL, NULL, &error_abort);
> >  }
> >  
> >  static void pc_dimm_realize(DeviceState *dev, Error **errp)
> > diff --git a/include/hw/mem/pc-dimm.h b/include/hw/mem/pc-dimm.h
> > index 1e483f2..99c4dfd 100644
> > --- a/include/hw/mem/pc-dimm.h
> > +++ b/include/hw/mem/pc-dimm.h
> > @@ -33,6 +33,7 @@
> >  #define PC_DIMM_NODE_PROP "node"
> >  #define PC_DIMM_SIZE_PROP "size"
> >  #define PC_DIMM_MEMDEV_PROP "memdev"
> > +#define PC_DIMM_RSVD_PROP "reserved-size"
> >  
> >  #define PC_DIMM_UNASSIGNED_SLOT -1
> >  
> > @@ -53,6 +54,7 @@ typedef struct PCDIMMDevice {
> >      uint64_t addr;
> >      uint32_t node;
> >      int32_t slot;
> > +    uint64_t reserved_size;
> >      HostMemoryBackend *hostmem;
> >  } PCDIMMDevice;
> >  
> > -- 
> > 2.10.1
> > 
> >