Re: [PATCH v3 3/3] spapr: nvdimm: Enable sync-dax device property for nvdimm

[David Gibson]

On Tue, Mar 23, 2021 at 09:47:55AM -0400, Shivaprasad G Bhat wrote:
> The patch adds the 'sync-dax' property to the nvdimm device.
> 
> When the sync-dax is 'off', the device tree property
> "hcall-flush-required" is added to the nvdimm node which makes the
> guest to issue H_SCM_FLUSH hcalls to request for flushes explicitly.
> This would be the default behaviour without sync-dax property set
> for the nvdimm device.
> 
> The sync-dax="on" would mean the guest need not make flush requests
> to the qemu. On previous machine versions the sync-dax is set to be
> "on" by default using the hw_compat magic.
> 
> Signed-off-by: Shivaprasad G Bhat <sbhat@linux.ibm.com>
> ---
>  hw/core/machine.c       |    1 +
>  hw/mem/nvdimm.c         |    1 +
>  hw/ppc/spapr_nvdimm.c   |   17 +++++++++++++++++
>  include/hw/mem/nvdimm.h |   10 ++++++++++
>  include/hw/ppc/spapr.h  |    1 +
>  5 files changed, 30 insertions(+)
> 
> diff --git a/hw/core/machine.c b/hw/core/machine.c
> index 257a664ea2..f843643574 100644
> --- a/hw/core/machine.c
> +++ b/hw/core/machine.c
> @@ -41,6 +41,7 @@ GlobalProperty hw_compat_5_2[] = {
>      { "PIIX4_PM", "smm-compat", "on"},
>      { "virtio-blk-device", "report-discard-granularity", "off" },
>      { "virtio-net-pci", "vectors", "3"},
> +    { "nvdimm", "sync-dax", "on" },
>  };
>  const size_t hw_compat_5_2_len = G_N_ELEMENTS(hw_compat_5_2);
>  
> diff --git a/hw/mem/nvdimm.c b/hw/mem/nvdimm.c
> index 7397b67156..8f0e29b191 100644
> --- a/hw/mem/nvdimm.c
> +++ b/hw/mem/nvdimm.c
> @@ -229,6 +229,7 @@ static void nvdimm_write_label_data(NVDIMMDevice *nvdimm, 
> const void *buf,
>  
>  static Property nvdimm_properties[] = {
>      DEFINE_PROP_BOOL(NVDIMM_UNARMED_PROP, NVDIMMDevice, unarmed, false),
> +    DEFINE_PROP_BOOL(NVDIMM_SYNC_DAX_PROP, NVDIMMDevice, sync_dax, false),

I'm a bit uncomfortable adding this base NVDIMM property without at
least some logic about how it's handled on non-PAPR platforms.

>      DEFINE_PROP_END_OF_LIST(),
>  };
>  
> diff --git a/hw/ppc/spapr_nvdimm.c b/hw/ppc/spapr_nvdimm.c
> index 883317c1ed..dd1c90251b 100644
> --- a/hw/ppc/spapr_nvdimm.c
> +++ b/hw/ppc/spapr_nvdimm.c
> @@ -125,6 +125,9 @@ static int spapr_dt_nvdimm(SpaprMachineState *spapr, void 
> *fdt,
>      uint64_t lsize = nvdimm->label_size;
>      uint64_t size = object_property_get_int(OBJECT(nvdimm), 
> PC_DIMM_SIZE_PROP,
>                                              NULL);
> +    bool sync_dax = object_property_get_bool(OBJECT(nvdimm),
> +                                             NVDIMM_SYNC_DAX_PROP,
> +                                             &error_abort);
>  
>      drc = spapr_drc_by_id(TYPE_SPAPR_DRC_PMEM, slot);
>      g_assert(drc);
> @@ -159,6 +162,11 @@ static int spapr_dt_nvdimm(SpaprMachineState *spapr, 
> void *fdt,
>                               "operating-system")));
>      _FDT(fdt_setprop(fdt, child_offset, "ibm,cache-flush-required", NULL, 
> 0));
>  
> +    if (!sync_dax) {
> +        _FDT(fdt_setprop(fdt, child_offset, "ibm,hcall-flush-required",
> +                         NULL, 0));
> +    }
> +
>      return child_offset;
>  }
>  
> @@ -567,10 +575,12 @@ static target_ulong h_scm_flush(PowerPCCPU *cpu, 
> SpaprMachineState *spapr,
>                                        target_ulong opcode, target_ulong 
> *args)
>  {
>      int ret;
> +    bool sync_dax;
>      uint32_t drc_index = args[0];
>      uint64_t continue_token = args[1];
>      SpaprDrc *drc = spapr_drc_by_index(drc_index);
>      PCDIMMDevice *dimm;
> +    NVDIMMDevice *nvdimm;
>      HostMemoryBackend *backend = NULL;
>      SpaprNVDIMMDeviceFlushState *state;
>      ThreadPool *pool = aio_get_thread_pool(qemu_get_aio_context());
> @@ -580,6 +590,13 @@ static target_ulong h_scm_flush(PowerPCCPU *cpu, 
> SpaprMachineState *spapr,
>          return H_PARAMETER;
>      }
>  
> +    nvdimm = NVDIMM(drc->dev);
> +    sync_dax = object_property_get_bool(OBJECT(nvdimm), NVDIMM_SYNC_DAX_PROP,
> +                                        &error_abort);
> +    if (sync_dax) {
> +        return H_UNSUPPORTED;

Do you want to return UNSUPPORTED here, or just H_SUCCESS, since the
flush should be a no-op in this case.

> +    }
> +
>      if (continue_token != 0) {
>          ret = spapr_nvdimm_get_flush_status(continue_token);
>          if (H_IS_LONG_BUSY(ret)) {
> diff --git a/include/hw/mem/nvdimm.h b/include/hw/mem/nvdimm.h
> index bcf62f825c..f82979cf2f 100644
> --- a/include/hw/mem/nvdimm.h
> +++ b/include/hw/mem/nvdimm.h
> @@ -51,6 +51,7 @@ OBJECT_DECLARE_TYPE(NVDIMMDevice, NVDIMMClass, NVDIMM)
>  #define NVDIMM_LABEL_SIZE_PROP "label-size"
>  #define NVDIMM_UUID_PROP       "uuid"
>  #define NVDIMM_UNARMED_PROP    "unarmed"
> +#define NVDIMM_SYNC_DAX_PROP   "sync-dax"
>  
>  struct NVDIMMDevice {
>      /* private */
> @@ -85,6 +86,15 @@ struct NVDIMMDevice {
>       */
>      bool unarmed;
>  
> +    /*
> +     * On PPC64,
> +     * The 'off' value results in the hcall-flush-required property set
> +     * in the device tree for pseries machines. When 'off', the guest
> +     * initiates explicit flush requests to the backend device ensuring
> +     * write persistence.
> +     */
> +    bool sync_dax;
> +
>      /*
>       * The PPC64 - spapr requires each nvdimm device have a uuid.
>       */
> diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
> index 7c27fb3e2d..51c35488a4 100644
> --- a/include/hw/ppc/spapr.h
> +++ b/include/hw/ppc/spapr.h
> @@ -333,6 +333,7 @@ struct SpaprMachineState {
>  #define H_P7              -60
>  #define H_P8              -61
>  #define H_P9              -62
> +#define H_UNSUPPORTED     -67
>  #define H_OVERLAP         -68
>  #define H_UNSUPPORTED_FLAG -256
>  #define H_MULTI_THREADS_ACTIVE -9005
> 
> 

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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