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SubjectRe: [PATCH] ocxl: Allow contexts to be attached with a NULL mm
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On 17/6/19 2:41 pm, Alastair D'Silva wrote:
> From: Alastair D'Silva <alastair@d-silva.org>
>
> If an OpenCAPI context is to be used directly by a kernel driver, there
> may not be a suitable mm to use.
>
> The patch makes the mm parameter to ocxl_context_attach optional.
>
> Signed-off-by: Alastair D'Silva <alastair@d-silva.org>

The one issue I can see here is that using mm == NULL bypasses our
method of enabling/disabling global TLBIs in mm_context_add_copro().

Discussing this privately with Alastair and Fred - this should be fine,
but perhaps we should document that.

> ---
> drivers/misc/ocxl/context.c | 9 ++++++---
> drivers/misc/ocxl/link.c | 12 ++++++++----
> 2 files changed, 14 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/misc/ocxl/context.c b/drivers/misc/ocxl/context.c
> index bab9c9364184..994563a078eb 100644
> --- a/drivers/misc/ocxl/context.c
> +++ b/drivers/misc/ocxl/context.c
> @@ -69,6 +69,7 @@ static void xsl_fault_error(void *data, u64 addr, u64 dsisr)
> int ocxl_context_attach(struct ocxl_context *ctx, u64 amr, struct mm_struct *mm)
> {
> int rc;
> + unsigned long pidr = 0;
>
> // Locks both status & tidr
> mutex_lock(&ctx->status_mutex);
> @@ -77,9 +78,11 @@ int ocxl_context_attach(struct ocxl_context *ctx, u64 amr, struct mm_struct *mm)
> goto out;
> }
>
> - rc = ocxl_link_add_pe(ctx->afu->fn->link, ctx->pasid,
> - mm->context.id, ctx->tidr, amr, mm,
> - xsl_fault_error, ctx);
> + if (mm)
> + pidr = mm->context.id;
> +
> + rc = ocxl_link_add_pe(ctx->afu->fn->link, ctx->pasid, pidr, ctx->tidr,
> + amr, mm, xsl_fault_error, ctx);
> if (rc)
> goto out;
>
> diff --git a/drivers/misc/ocxl/link.c b/drivers/misc/ocxl/link.c
> index cce5b0d64505..43542f124807 100644
> --- a/drivers/misc/ocxl/link.c
> +++ b/drivers/misc/ocxl/link.c
> @@ -523,7 +523,8 @@ int ocxl_link_add_pe(void *link_handle, int pasid, u32 pidr, u32 tidr,
> pe->amr = cpu_to_be64(amr);
> pe->software_state = cpu_to_be32(SPA_PE_VALID);
>
> - mm_context_add_copro(mm);
> + if (mm)
> + mm_context_add_copro(mm);
> /*
> * Barrier is to make sure PE is visible in the SPA before it
> * is used by the device. It also helps with the global TLBI
> @@ -546,7 +547,8 @@ int ocxl_link_add_pe(void *link_handle, int pasid, u32 pidr, u32 tidr,
> * have a reference on mm_users. Incrementing mm_count solves
> * the problem.
> */
> - mmgrab(mm);
> + if (mm)
> + mmgrab(mm);
> trace_ocxl_context_add(current->pid, spa->spa_mem, pasid, pidr, tidr);
> unlock:
> mutex_unlock(&spa->spa_lock);
> @@ -652,8 +654,10 @@ int ocxl_link_remove_pe(void *link_handle, int pasid)
> if (!pe_data) {
> WARN(1, "Couldn't find pe data when removing PE\n");
> } else {
> - mm_context_remove_copro(pe_data->mm);
> - mmdrop(pe_data->mm);
> + if (pe_data->mm) {
> + mm_context_remove_copro(pe_data->mm);
> + mmdrop(pe_data->mm);
> + }
> kfree_rcu(pe_data, rcu);
> }
> unlock:
>

--
Andrew Donnellan OzLabs, ADL Canberra
ajd@linux.ibm.com IBM Australia Limited

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