Re: [Qemu-devel] [PATCH v2] hw/ppc/spapr: Fix segfault when instantiating a 'pc-dimm' without 'memdev'

[Pankaj Gupta <pagupta@redhat.com>]

Hello Thomas,

> 
> QEMU currently crashes when trying to use a 'pc-dimm' on the pseries
> machine without specifying its 'memdev' property. This happens because
> pc_dimm_get_memory_region() does not check whether the 'memdev' property
> has properly been set by the user. Looking closer at this function, it's
> also obvious that it is using &error_abort to call another function - and
> this is bad in a function that is used in the hot-plugging calling chain
> since this can also cause QEMU to exit unexpectedly.

In place of checking if 'memdev' is already allocated/present while fetching 
'get_functions' every place. If 'memdev' is required for memory hotplug operation 
can we just put a check at some common place and don't start or instantiate if 
'memdev' is not present.

I can see:

'pc_dimm_realize' function checks for : in my case prints warning
and avoid Qemu to start.
...
...
if (!dimm->hostmem) {
        error_setg(errp, "'" PC_DIMM_MEMDEV_PROP "' property is not set");
        return;
    } 
...

Thanks,
Pankaj

> 
> So let's fix these issues in a proper way now: Add a "Error **errp"
> parameter to pc_dimm_get_memory_region() which we use in case the 'memdev'
> property has not been set by the user, and which we can use instead of
> the &error_abort, and change the callers of get_memory_region() to make
> use of this "errp" parameter for proper error checking.
> 
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>  hw/i386/pc.c             | 14 ++++++++++++--
>  hw/mem/nvdimm.c          |  2 +-
>  hw/mem/pc-dimm.c         | 14 +++++++++++---
>  hw/ppc/spapr.c           | 42 ++++++++++++++++++++++++++++++------------
>  include/hw/mem/pc-dimm.h |  2 +-
>  5 files changed, 55 insertions(+), 19 deletions(-)
> 
> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> index 5943539..2108104 100644
> --- a/hw/i386/pc.c
> +++ b/hw/i386/pc.c
> @@ -1691,10 +1691,15 @@ static void pc_dimm_plug(HotplugHandler *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);
> +    MemoryRegion *mr;
>      uint64_t align = TARGET_PAGE_SIZE;
>      bool is_nvdimm = object_dynamic_cast(OBJECT(dev), TYPE_NVDIMM);
>  
> +    mr = ddc->get_memory_region(dimm, &local_err);
> +    if (local_err) {
> +        goto out;
> +    }
> +
>      if (memory_region_get_alignment(mr) && pcmc->enforce_aligned_dimm) {
>          align = memory_region_get_alignment(mr);
>      }
> @@ -1758,10 +1763,15 @@ static void pc_dimm_unplug(HotplugHandler
> *hotplug_dev,
>      PCMachineState *pcms = PC_MACHINE(hotplug_dev);
>      PCDIMMDevice *dimm = PC_DIMM(dev);
>      PCDIMMDeviceClass *ddc = PC_DIMM_GET_CLASS(dimm);
> -    MemoryRegion *mr = ddc->get_memory_region(dimm);
> +    MemoryRegion *mr;
>      HotplugHandlerClass *hhc;
>      Error *local_err = NULL;
>  
> +    mr = ddc->get_memory_region(dimm, &local_err);
> +    if (local_err) {
> +        goto out;
> +    }
> +
>      hhc = HOTPLUG_HANDLER_GET_CLASS(pcms->acpi_dev);
>      hhc->unplug(HOTPLUG_HANDLER(pcms->acpi_dev), dev, &local_err);
>  
> diff --git a/hw/mem/nvdimm.c b/hw/mem/nvdimm.c
> index db896b0..952fce5 100644
> --- a/hw/mem/nvdimm.c
> +++ b/hw/mem/nvdimm.c
> @@ -71,7 +71,7 @@ static void nvdimm_init(Object *obj)
>                          NULL, NULL);
>  }
>  
> -static MemoryRegion *nvdimm_get_memory_region(PCDIMMDevice *dimm)
> +static MemoryRegion *nvdimm_get_memory_region(PCDIMMDevice *dimm, Error
> **errp)
>  {
>      NVDIMMDevice *nvdimm = NVDIMM(dimm);
>  
> diff --git a/hw/mem/pc-dimm.c b/hw/mem/pc-dimm.c
> index ea67b46..bdf6649 100644
> --- a/hw/mem/pc-dimm.c
> +++ b/hw/mem/pc-dimm.c
> @@ -363,7 +363,10 @@ static void pc_dimm_get_size(Object *obj, Visitor *v,
> const char *name,
>      PCDIMMDevice *dimm = PC_DIMM(obj);
>      PCDIMMDeviceClass *ddc = PC_DIMM_GET_CLASS(obj);
>  
> -    mr = ddc->get_memory_region(dimm);
> +    mr = ddc->get_memory_region(dimm, errp);
> +    if (!mr) {
> +        return;
> +    }
>      value = memory_region_size(mr);
>  
>      visit_type_uint64(v, name, &value, errp);
> @@ -411,9 +414,14 @@ static void pc_dimm_unrealize(DeviceState *dev, Error
> **errp)
>      host_memory_backend_set_mapped(dimm->hostmem, false);
>  }
>  
> -static MemoryRegion *pc_dimm_get_memory_region(PCDIMMDevice *dimm)
> +static MemoryRegion *pc_dimm_get_memory_region(PCDIMMDevice *dimm, Error
> **errp)
>  {
> -    return host_memory_backend_get_memory(dimm->hostmem, &error_abort);
> +    if (!dimm->hostmem) {
> +        error_setg(errp, "'" PC_DIMM_MEMDEV_PROP "' property must be set");
> +        return NULL;
> +    }
> +
> +    return host_memory_backend_get_memory(dimm->hostmem, errp);
>  }
>  
>  static MemoryRegion *pc_dimm_get_vmstate_memory_region(PCDIMMDevice *dimm)
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index f7a1972..cec441c 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -2772,10 +2772,15 @@ static void spapr_memory_plug(HotplugHandler
> *hotplug_dev, DeviceState *dev,
>      sPAPRMachineState *ms = SPAPR_MACHINE(hotplug_dev);
>      PCDIMMDevice *dimm = PC_DIMM(dev);
>      PCDIMMDeviceClass *ddc = PC_DIMM_GET_CLASS(dimm);
> -    MemoryRegion *mr = ddc->get_memory_region(dimm);
> -    uint64_t align = memory_region_get_alignment(mr);
> -    uint64_t size = memory_region_size(mr);
> -    uint64_t addr;
> +    MemoryRegion *mr;
> +    uint64_t align, size, addr;
> +
> +    mr = ddc->get_memory_region(dimm, &local_err);
> +    if (local_err) {
> +        goto out;
> +    }
> +    align = memory_region_get_alignment(mr);
> +    size = memory_region_size(mr);
>  
>      pc_dimm_memory_plug(dev, &ms->hotplug_memory, mr, align, &local_err);
>      if (local_err) {
> @@ -2808,10 +2813,16 @@ static void spapr_memory_pre_plug(HotplugHandler
> *hotplug_dev, DeviceState *dev,
>  {
>      PCDIMMDevice *dimm = PC_DIMM(dev);
>      PCDIMMDeviceClass *ddc = PC_DIMM_GET_CLASS(dimm);
> -    MemoryRegion *mr = ddc->get_memory_region(dimm);
> -    uint64_t size = memory_region_size(mr);
> +    MemoryRegion *mr;
> +    uint64_t size;
>      char *mem_dev;
>  
> +    mr = ddc->get_memory_region(dimm, errp);
> +    if (!mr) {
> +        return;
> +    }
> +    size = memory_region_size(mr);
> +
>      if (size % SPAPR_MEMORY_BLOCK_SIZE) {
>          error_setg(errp, "Hotplugged memory size must be a multiple of "
>                        "%lld MB", SPAPR_MEMORY_BLOCK_SIZE / M_BYTE);
> @@ -2882,7 +2893,7 @@ static sPAPRDIMMState
> *spapr_recover_pending_dimm_state(sPAPRMachineState *ms,
>  {
>      sPAPRDRConnector *drc;
>      PCDIMMDeviceClass *ddc = PC_DIMM_GET_CLASS(dimm);
> -    MemoryRegion *mr = ddc->get_memory_region(dimm);
> +    MemoryRegion *mr = ddc->get_memory_region(dimm, &error_abort);
>      uint64_t size = memory_region_size(mr);
>      uint32_t nr_lmbs = size / SPAPR_MEMORY_BLOCK_SIZE;
>      uint32_t avail_lmbs = 0;
> @@ -2912,7 +2923,7 @@ void spapr_lmb_release(DeviceState *dev)
>      sPAPRMachineState *spapr = SPAPR_MACHINE(qdev_get_hotplug_handler(dev));
>      PCDIMMDevice *dimm = PC_DIMM(dev);
>      PCDIMMDeviceClass *ddc = PC_DIMM_GET_CLASS(dimm);
> -    MemoryRegion *mr = ddc->get_memory_region(dimm);
> +    MemoryRegion *mr = ddc->get_memory_region(dimm, &error_abort);
>      sPAPRDIMMState *ds = spapr_pending_dimm_unplugs_find(spapr,
>      PC_DIMM(dev));
>  
>      /* This information will get lost if a migration occurs
> @@ -2945,12 +2956,19 @@ static void
> spapr_memory_unplug_request(HotplugHandler *hotplug_dev,
>      Error *local_err = NULL;
>      PCDIMMDevice *dimm = PC_DIMM(dev);
>      PCDIMMDeviceClass *ddc = PC_DIMM_GET_CLASS(dimm);
> -    MemoryRegion *mr = ddc->get_memory_region(dimm);
> -    uint64_t size = memory_region_size(mr);
> -    uint32_t nr_lmbs = size / SPAPR_MEMORY_BLOCK_SIZE;
> -    uint64_t addr_start, addr;
> +    MemoryRegion *mr;
> +    uint32_t nr_lmbs;
> +    uint64_t size, addr_start, addr;
>      int i;
>      sPAPRDRConnector *drc;
> +
> +    mr = ddc->get_memory_region(dimm, &local_err);
> +    if (local_err) {
> +        goto out;
> +    }
> +    size = memory_region_size(mr);
> +    nr_lmbs = size / SPAPR_MEMORY_BLOCK_SIZE;
> +
>      addr_start = object_property_get_uint(OBJECT(dimm), PC_DIMM_ADDR_PROP,
>                                           &local_err);
>      if (local_err) {
> diff --git a/include/hw/mem/pc-dimm.h b/include/hw/mem/pc-dimm.h
> index 1e483f2..6f8c3eb 100644
> --- a/include/hw/mem/pc-dimm.h
> +++ b/include/hw/mem/pc-dimm.h
> @@ -71,7 +71,7 @@ typedef struct PCDIMMDeviceClass {
>  
>      /* public */
>      void (*realize)(PCDIMMDevice *dimm, Error **errp);
> -    MemoryRegion *(*get_memory_region)(PCDIMMDevice *dimm);
> +    MemoryRegion *(*get_memory_region)(PCDIMMDevice *dimm, Error **errp);
>      MemoryRegion *(*get_vmstate_memory_region)(PCDIMMDevice *dimm);
>  } PCDIMMDeviceClass;
>  
> --
> 1.8.3.1
> 
> 
>