linux-kernel - [PATCH] ocxl: Allow contexts to be attached with a NULL mm

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Message-Id: <20190617044152.13707-1-alastair@au1.ibm.com>
Date:   Mon, 17 Jun 2019 14:41:52 +1000
From:   "Alastair D'Silva" <alastair@....ibm.com>
To:     alastair@...ilva.org
Cc:     Frederic Barrat <fbarrat@...ux.ibm.com>,
        Andrew Donnellan <ajd@...ux.ibm.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: [PATCH] ocxl: Allow contexts to be attached with a NULL mm

From: Alastair D'Silva <alastair@...ilva.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@...ilva.org>
---
 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:
-- 
2.21.0