Re: [PATCH 2/2] cxl: Enable global TLBIs for cxl contexts

Le 28/08/2017 à 14:03, Benjamin Herrenschmidt a écrit :

On Mon, 2017-08-28 at 10:47 +0200, Frederic Barrat wrote:

quoted

     
Signed-off-by: Frederic Barrat <redacted>

diff --git a/arch/powerpc/include/asm/mmu_context.h b/arch/powerpc/include/asm/mmu_context.h
index 309592589e30..6447c0df7ec4 100644
--- a/arch/powerpc/include/asm/mmu_context.h
+++ b/arch/powerpc/include/asm/mmu_context.h

@@ -77,6 +77,41 @@ extern void switch_cop(struct mm_struct *next);
  extern int use_cop(unsigned long acop, struct mm_struct *mm);
  extern void drop_cop(unsigned long acop, struct mm_struct *mm);
  
+#ifdef CONFIG_PPC_BOOK3S_64
+static inline void inc_mm_active_cpus(struct mm_struct *mm)
+{
+	atomic_inc(&mm->context.active_cpus);
+}
+
+static inline void dec_mm_active_cpus(struct mm_struct *mm)
+{
+	atomic_dec(&mm->context.active_cpus);
+}
+
+static inline void mm_context_add_copro(struct mm_struct *mm)
+{
+	inc_mm_active_cpus(mm);
+}
+
+static inline void mm_context_remove_copro(struct mm_struct *mm)
+{
+	/*
+	 * Need to broadcast a global flush of the full mm before
+	 * decrementing active_cpus count, as the next TLBI may be
+	 * local and the nMMU and/or PSL need to be cleaned up.
+	 * Should be rare enough so that it's acceptable.
+	 */
+	flush_tlb_mm(mm);
+	dec_mm_active_cpus(mm);
+}

You probably need to kill the pwc too. With my recent optimizations
flush_tlb_mm won't do that anymore. You need a bigger hammer (I don't
have the code at hand right now to tell you what exactly :-) Basically
something that does a RIC_FLUSH_ALL.

Good point, I had missed the change. It looks like I now need to call 
radix__flush_all_mm(), which I would have to export outside of 
tlb-radix.c first.

Any problem with having a flush_all_mm() to complement a flush_tlb_mm()? 
It's tainted with radix, and the 2 would be equivalent on hash, but it 
would make things easy.

   Fred

quoted

+#else
+static inline void inc_mm_active_cpus(struct mm_struct *mm) { }
+static inline void dec_mm_active_cpus(struct mm_struct *mm) { }
+static inline void mm_context_add_copro(struct mm_struct *mm) { }
+static inline void mm_context_remove_copro(struct mm_struct *mm) { }
+#endif
+
+
  extern void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
  			       struct task_struct *tsk);
  

diff --git a/arch/powerpc/mm/mmu_context.c b/arch/powerpc/mm/mmu_context.c
index 0f613bc63c50..d60a62bf4fc7 100644
--- a/arch/powerpc/mm/mmu_context.c
+++ b/arch/powerpc/mm/mmu_context.c

@@ -34,15 +34,6 @@ static inline void switch_mm_pgdir(struct task_struct *tsk,
  				   struct mm_struct *mm) { }
  #endif
  
-#ifdef CONFIG_PPC_BOOK3S_64
-static inline void inc_mm_active_cpus(struct mm_struct *mm)
-{
-	atomic_inc(&mm->context.active_cpus);
-}
-#else
-static inline void inc_mm_active_cpus(struct mm_struct *mm) { }
-#endif
-
  void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
  			struct task_struct *tsk)
  {

diff --git a/drivers/misc/cxl/api.c b/drivers/misc/cxl/api.c
index e0dfd1eadd70..33daf33e0e05 100644
--- a/drivers/misc/cxl/api.c
+++ b/drivers/misc/cxl/api.c

@@ -15,6 +15,7 @@
  #include <linux/module.h>
  #include <linux/mount.h>
  #include <linux/sched/mm.h>
+#include <linux/mmu_context.h>
  
  #include "cxl.h"
  

@@ -332,8 +333,11 @@ int cxl_start_context(struct cxl_context *ctx, u64 wed,
  		cxl_context_mm_count_get(ctx);
  
  		/* decrement the use count */
-		if (ctx->mm)
+		if (ctx->mm) {
  			mmput(ctx->mm);
+			/* make TLBIs for this context global */
+			mm_context_add_copro(ctx->mm);
+		}
  	}
  
  	/*

@@ -342,13 +346,25 @@ int cxl_start_context(struct cxl_context *ctx, u64 wed,
  	 */
  	cxl_ctx_get();
  
+	/*
+	 * Barrier is needed to make sure all TLBIs are global before
+	 * we attach and the context starts being used by the adapter.
+	 *
+	 * Needed after mm_context_add_copro() for radix and
+	 * cxl_ctx_get() for hash/p8
+	 */
+	smp_mb();
+
  	if ((rc = cxl_ops->attach_process(ctx, kernel, wed, 0))) {
  		put_pid(ctx->pid);
  		ctx->pid = NULL;
  		cxl_adapter_context_put(ctx->afu->adapter);
  		cxl_ctx_put();
-		if (task)
+		if (task) {
  			cxl_context_mm_count_put(ctx);
+			if (ctx->mm)
+				mm_context_remove_copro(ctx->mm);
+		}
  		goto out;
  	}
  

diff --git a/drivers/misc/cxl/context.c b/drivers/misc/cxl/context.c
index 8c32040b9c09..12a41b2753f0 100644
--- a/drivers/misc/cxl/context.c
+++ b/drivers/misc/cxl/context.c

@@ -18,6 +18,7 @@
  #include <linux/slab.h>
  #include <linux/idr.h>
  #include <linux/sched/mm.h>
+#include <linux/mmu_context.h>
  #include <asm/cputable.h>
  #include <asm/current.h>
  #include <asm/copro.h>

@@ -267,6 +268,8 @@ int __detach_context(struct cxl_context *ctx)
  
  	/* Decrease the mm count on the context */
  	cxl_context_mm_count_put(ctx);
+	if (ctx->mm)
+		mm_context_remove_copro(ctx->mm);
  	ctx->mm = NULL;
  
  	return 0;

diff --git a/drivers/misc/cxl/file.c b/drivers/misc/cxl/file.c
index b76a491a485d..411e83cbbd82 100644
--- a/drivers/misc/cxl/file.c
+++ b/drivers/misc/cxl/file.c

@@ -19,6 +19,7 @@
  #include <linux/mm.h>
  #include <linux/slab.h>
  #include <linux/sched/mm.h>
+#include <linux/mmu_context.h>
  #include <asm/cputable.h>
  #include <asm/current.h>
  #include <asm/copro.h>

@@ -220,9 +221,12 @@ static long afu_ioctl_start_work(struct cxl_context *ctx,
  	/* ensure this mm_struct can't be freed */
  	cxl_context_mm_count_get(ctx);
  
-	/* decrement the use count */
-	if (ctx->mm)
+	if (ctx->mm) {
+		/* decrement the use count */
  		mmput(ctx->mm);
+		/* make TLBIs for this context global */
+		mm_context_add_copro(ctx->mm);
+	}
  
  	/*
  	 * Increment driver use count. Enables global TLBIs for hash

@@ -230,6 +234,15 @@ static long afu_ioctl_start_work(struct cxl_context *ctx,
  	 */
  	cxl_ctx_get();
  
+	/*
+	 * Barrier is needed to make sure all TLBIs are global before
+	 * we attach and the context starts being used by the adapter.
+	 *
+	 * Needed after mm_context_add_copro() for radix and
+	 * cxl_ctx_get() for hash/p8
+	 */
+	smp_mb();
+
  	trace_cxl_attach(ctx, work.work_element_descriptor, work.num_interrupts, amr);
  
  	if ((rc = cxl_ops->attach_process(ctx, false, work.work_element_descriptor,

@@ -240,6 +253,8 @@ static long afu_ioctl_start_work(struct cxl_context *ctx,
  		ctx->pid = NULL;
  		cxl_ctx_put();
  		cxl_context_mm_count_put(ctx);
+		if (ctx->mm)
+			mm_context_remove_copro(ctx->mm);
  		goto out;
  	}