[PATCH v5 4/4] powerpc/papr_scm: Force a scm-unbind if initial scm-bind fails

[Laurent Dufour]

Le 23/07/2019 à 18:13, Vaibhav Jain a écrit :
> In some cases initial bind of scm memory for an lpar can fail if
> previously it wasn't released using a scm-unbind hcall. This situation
> can arise due to panic of the previous kernel or forced lpar
> fadump. In such cases the H_SCM_BIND_MEM return a H_OVERLAP error.
> 
> To mitigate such cases the patch updates papr_scm_probe() to force a
> call to drc_pmem_unbind() in case the initial bind of scm memory fails
> with EBUSY error. In case scm-bind operation again fails after the
> forced scm-unbind then we follow the existing error path. We also
> update drc_pmem_bind() to handle the H_OVERLAP error returned by phyp
> and indicate it as a EBUSY error back to the caller.
> 
> Suggested-by: "Oliver O'Halloran" <oohall at gmail.com>
> Signed-off-by: Vaibhav Jain <vaibhav at linux.ibm.com>
> Reviewed-by: Oliver O'Halloran <oohall at gmail.com>
> ---
> Change-log:
> 
> v5:
> * None. Re-spinning the patchset.
> 
> v4:
> * None. Re-spinning the patchset.
> 
> v3:
> * Minor update to a code comment. [Oliver]
> 
> v2:
> * Moved the retry code from drc_pmem_bind() to papr_scm_probe()
>    [Oliver]
> * Changed the type of variable 'rc' in drc_pmem_bind() to
>    int64_t. [Oliver]
> ---
>   arch/powerpc/platforms/pseries/papr_scm.c | 15 ++++++++++++++-
>   1 file changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/platforms/pseries/papr_scm.c b/arch/powerpc/platforms/pseries/papr_scm.c
> index 82568a7e0a7c..2c07908359b2 100644
> --- a/arch/powerpc/platforms/pseries/papr_scm.c
> +++ b/arch/powerpc/platforms/pseries/papr_scm.c
> @@ -44,8 +44,9 @@ struct papr_scm_priv {
>   static int drc_pmem_bind(struct papr_scm_priv *p)
>   {
>   	unsigned long ret[PLPAR_HCALL_BUFSIZE];
> -	uint64_t rc, token;
>   	uint64_t saved = 0;
> +	uint64_t token;
> +	int64_t rc;
> 
>   	/*
>   	 * When the hypervisor cannot map all the requested memory in a single
> @@ -65,6 +66,10 @@ static int drc_pmem_bind(struct papr_scm_priv *p)
>   	} while (rc == H_BUSY);
> 
>   	if (rc) {
> +		/* H_OVERLAP needs a separate error path */
> +		if (rc == H_OVERLAP)
> +			return -EBUSY;
> +
>   		dev_err(&p->pdev->dev, "bind err: %lld\n", rc);
>   		return -ENXIO;
>   	}
> @@ -404,6 +409,14 @@ static int papr_scm_probe(struct platform_device *pdev)
> 
>   	/* request the hypervisor to bind this region to somewhere in memory */
>   	rc = drc_pmem_bind(p);
> +
> +	/* If phyp says drc memory still bound then force unbound and retry */
> +	if (rc == -EBUSY) {
> +		dev_warn(&pdev->dev, "Retrying bind after unbinding\n");
> +		drc_pmem_unbind(p);
> +		rc = drc_pmem_bind(p);

In the unlikely case where H_SCM_BIND_MEM is returning H_OVERLAP once the 
unbinding has been done, the error would be silently processed. That sounds 
really unlikely, but should an error message be displayed in this 
particular case ?

> +	}
> +
>   	if (rc)
>   		goto err;
>