Re: [PATCH v2] ppc/spapr: Add support for implement support for H_SCM_HEALTH

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, Apr 01, 2021 at 06:35:19AM +0530, Vaibhav Jain 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.
> 
> 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#n220
> [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>

As well as the handful of comments below, this will definitely need to
wait for ppc-6.1 at this point.

> ---
> Changelog
> 
> v2:
> * Added a check for drc->dev to ensure that the dimm is plugged in
>   when servicing H_SCM_HEALTH. [ Shiva ]
> * Instead of accessing the 'nvdimm->unarmed' member directly use the
>   object_property_get_bool accessor to fetch it. [ Shiva ]
> * Update the usage of PAPR_PMEM_UNARMED* macros [ Greg ]
> * Updated patch description reference#1 to point appropriate section
>   in the documentation. [ Greg ]
> ---
>  hw/ppc/spapr_nvdimm.c  | 38 ++++++++++++++++++++++++++++++++++++++
>  include/hw/ppc/spapr.h |  3 ++-
>  2 files changed, 40 insertions(+), 1 deletion(-)
> 
> diff --git a/hw/ppc/spapr_nvdimm.c b/hw/ppc/spapr_nvdimm.c
> index b46c36917c..34096e4718 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. Taken from kernel's papr_scm.c */
> +/* SCM device is unable to persist memory contents */
> +#define PAPR_PMEM_UNARMED (1ULL << (63 - 0))

You can use PPC_BIT() for more clarity here.

> +/* Bits status indicators for health bitmap indicating unarmed dimm */
> +#define PAPR_PMEM_UNARMED_MASK (PAPR_PMEM_UNARMED)

I'm not sure why you want two equal #defines here.

> +
>  bool spapr_nvdimm_validate(HotplugHandler *hotplug_dev, NVDIMMDevice *nvdimm,
>                             uint64_t size, Error **errp)
>  {
> @@ -467,6 +474,36 @@ 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) {

This will fail badly if !drc (given index is way out of bounds).  I'm
pretty sure you want
	if (!drc || spapr_drc_type(drc) != SPAPR_DR_CONNECTOR_TYPE_PMEM) {


> +        return H_PARAMETER;
> +    }
> +
> +    /* Ensure that the dimm is plugged in */
> +    if (!drc->dev) {
> +        return H_HARDWARE;

H_HARDWARE doesn't seem right - it's the guest that has chosen to
attempt this on an unplugged LMB, not the (virtual) hardware's fault.

> +    }
> +
> +    nvdimm = NVDIMM(drc->dev);
> +
> +    args[0] = 0;
> +    /* Check if the nvdimm is unarmed and send its status via health bitmaps */
> +    if (object_property_get_bool(OBJECT(nvdimm), NVDIMM_UNARMED_PROP, NULL)) {
> +        args[0] |= PAPR_PMEM_UNARMED;
> +    }
> +
> +    /* Update the health bitmap with the applicable mask */
> +    args[1] = PAPR_PMEM_UNARMED_MASK;
> +
> +    return H_SUCCESS;
> +}
> +
>  static void spapr_scm_register_types(void)
>  {
>      /* qemu/scm specific hcalls */
> @@ -475,6 +512,7 @@ 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..6e1eafb05d 100644
> --- a/include/hw/ppc/spapr.h
> +++ b/include/hw/ppc/spapr.h
> @@ -538,8 +538,9 @@ struct SpaprMachineState {
>  #define H_SCM_BIND_MEM          0x3EC
>  #define H_SCM_UNBIND_MEM        0x3F0
>  #define H_SCM_UNBIND_ALL        0x3FC
> +#define H_SCM_HEALTH            0x400
>  
> -#define MAX_HCALL_OPCODE        H_SCM_UNBIND_ALL
> +#define MAX_HCALL_OPCODE        H_SCM_HEALTH
>  
>  /* The hcalls above are standardized in PAPR and implemented by pHyp
>   * as well.

-- 
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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