Re: [PATCH] ppc/spapr: Add support for implement support for H_SCM_HEALTH

[Greg Kurz]

Hi Vaibhav,

Great to see you around :-)

On Mon, 29 Mar 2021 21:52:59 +0530
Vaibhav Jain <vaibhav@linux.ibm.com> wrote:

> Add support for H_SCM_HEALTH hcall described at [1] for spapr
> nvdimms. This enables guest to detect the 'unarmed' status of a
> specific spapr nvdimm identified by its DRC and if its unarmed, mark
> the region backed by the nvdimm as read-only.
> 

Any chance that you can provide the documentation of this new hcall ?

> The patch adds h_scm_health() to handle the H_SCM_HEALTH hcall which
> returns two 64-bit bitmaps (health bitmap, health bitmap mask) derived
> from 'struct nvdimm->unarmed' member.
> 
> Linux kernel side changes to enable handling of 'unarmed' nvdimms for
> ppc64 are proposed at [2].
> 
> References:
> [1] "Hypercall Op-codes (hcalls)"
>     
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/powerpc/papr_hcalls.rst
> 
> [2] "powerpc/papr_scm: Mark nvdimm as unarmed if needed during probe"
>     
> https://lore.kernel.org/linux-nvdimm/20210329113103.476760-1-vaibhav@linux.ibm.com/
> 
> Signed-off-by: Vaibhav Jain <vaibhav@linux.ibm.com>
> ---
>  hw/ppc/spapr_nvdimm.c  | 30 ++++++++++++++++++++++++++++++
>  include/hw/ppc/spapr.h |  4 ++--
>  2 files changed, 32 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/ppc/spapr_nvdimm.c b/hw/ppc/spapr_nvdimm.c
> index b46c36917c..e38740036d 100644
> --- a/hw/ppc/spapr_nvdimm.c
> +++ b/hw/ppc/spapr_nvdimm.c
> @@ -31,6 +31,13 @@
>  #include "qemu/range.h"
>  #include "hw/ppc/spapr_numa.h"
>  
> +/* DIMM health bitmap bitmap indicators */
> +/* SCM device is unable to persist memory contents */
> +#define PAPR_PMEM_UNARMED (1ULL << (63 - 0))

This looks like PPC_BIT(0).

> +
> +/* Bits status indicators for health bitmap indicating unarmed dimm */
> +#define PAPR_PMEM_UNARMED_MASK (PAPR_PMEM_UNARMED)
> +
>  bool spapr_nvdimm_validate(HotplugHandler *hotplug_dev, NVDIMMDevice *nvdimm,
>                             uint64_t size, Error **errp)
>  {
> @@ -467,6 +474,28 @@ static target_ulong h_scm_unbind_all(PowerPCCPU *cpu, 
> SpaprMachineState *spapr,
>      return H_SUCCESS;
>  }
>  
> +static target_ulong h_scm_health(PowerPCCPU *cpu, SpaprMachineState *spapr,
> +                                 target_ulong opcode, target_ulong *args)
> +{
> +    uint32_t drc_index = args[0];
> +    SpaprDrc *drc = spapr_drc_by_index(drc_index);
> +    NVDIMMDevice *nvdimm;
> +
> +    if (drc && spapr_drc_type(drc) != SPAPR_DR_CONNECTOR_TYPE_PMEM) {
> +        return H_PARAMETER;
> +    }
> +
> +    nvdimm = NVDIMM(drc->dev);

Yeah as already suggested by Shiva, drc->dev should be checked like
in h_scm_bind_mem().

> +
> +    /* Check if the nvdimm is unarmed and send its status via health bitmaps 
> */
> +    args[0] = nvdimm->unarmed ? PAPR_PMEM_UNARMED_MASK : 0;
> +

Shouldn't ^^ use PAPR_PMEM_UNARMED then ?

> +    /* health bitmap mask same as the health bitmap */
> +    args[1] = args[0];
> +

If so, it seems that PAPR_PMEM_UNARMED_MASK isn't even needed.

Having access to the excerpts from the PAPR addendum that describes
this hcall would _really_ help in reviewing.

> +    return H_SUCCESS;
> +}
> +
>  static void spapr_scm_register_types(void)
>  {
>      /* qemu/scm specific hcalls */
> @@ -475,6 +504,7 @@ static void spapr_scm_register_types(void)
>      spapr_register_hypercall(H_SCM_BIND_MEM, h_scm_bind_mem);
>      spapr_register_hypercall(H_SCM_UNBIND_MEM, h_scm_unbind_mem);
>      spapr_register_hypercall(H_SCM_UNBIND_ALL, h_scm_unbind_all);
> +    spapr_register_hypercall(H_SCM_HEALTH, h_scm_health);
>  }
>  
>  type_init(spapr_scm_register_types)
> diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
> index 47cebaf3ac..18859b9ab2 100644
> --- a/include/hw/ppc/spapr.h
> +++ b/include/hw/ppc/spapr.h
> @@ -538,8 +538,8 @@ struct SpaprMachineState {
>  #define H_SCM_BIND_MEM          0x3EC
>  #define H_SCM_UNBIND_MEM        0x3F0
>  #define H_SCM_UNBIND_ALL        0x3FC
> -
> -#define MAX_HCALL_OPCODE        H_SCM_UNBIND_ALL
> +#define H_SCM_HEALTH            0x400
> +#define MAX_HCALL_OPCODE        H_SCM_HEALTH
>  
>  /* The hcalls above are standardized in PAPR and implemented by pHyp
>   * as well.