powerpc/powernv/npu-dma: Add explicit flush when sending an ATSD

NPU2 requires an extra explicit flush to an active GPU PID when
sending address translation shoot downs (ATSDs) to reliably flush the
GPU TLB. This patch adds just such a flush at the end of each sequence
of ATSDs.

We can safely use PID 0 which is always reserved and active on the
GPU. PID 0 is only used for init_mm which will never be a user mm on
the GPU. To enforce this we add a check in pnv_npu2_init_context()
just in case someone tries to use PID 0 on the GPU.
Signed-off-by: Alistair Popple <alistair@popple.id.au>
[mpe: Use true/false for bool literals]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/powernv/npu-dma.c

@@ -449,7 +449,7 @@ static int mmio_launch_invalidate(struct npu *npu, unsigned long launch,
 	return mmio_atsd_reg;
 }
 
-static int mmio_invalidate_pid(struct npu *npu, unsigned long pid)
+static int mmio_invalidate_pid(struct npu *npu, unsigned long pid, bool flush)
 {
 	unsigned long launch;
 
@@ -465,12 +465,15 @@ static int mmio_invalidate_pid(struct npu *npu, unsigned long pid)
 	/* PID */
 	launch |= pid << PPC_BITLSHIFT(38);
 
+	/* No flush */
+	launch |= !flush << PPC_BITLSHIFT(39);
+
 	/* Invalidating the entire process doesn't use a va */
 	return mmio_launch_invalidate(npu, launch, 0);
 }
 
 static int mmio_invalidate_va(struct npu *npu, unsigned long va,
-			unsigned long pid)
+			unsigned long pid, bool flush)
 {
 	unsigned long launch;
 
@@ -486,26 +489,60 @@ static int mmio_invalidate_va(struct npu *npu, unsigned long va,
 	/* PID */
 	launch |= pid << PPC_BITLSHIFT(38);
 
+	/* No flush */
+	launch |= !flush << PPC_BITLSHIFT(39);
+
 	return mmio_launch_invalidate(npu, launch, va);
 }
 
 #define mn_to_npu_context(x) container_of(x, struct npu_context, mn)
 
+struct mmio_atsd_reg {
+	struct npu *npu;
+	int reg;
+};
+
+static void mmio_invalidate_wait(
+	struct mmio_atsd_reg mmio_atsd_reg[NV_MAX_NPUS], bool flush)
+{
+	struct npu *npu;
+	int i, reg;
+
+	/* Wait for all invalidations to complete */
+	for (i = 0; i <= max_npu2_index; i++) {
+		if (mmio_atsd_reg[i].reg < 0)
+			continue;
+
+		/* Wait for completion */
+		npu = mmio_atsd_reg[i].npu;
+		reg = mmio_atsd_reg[i].reg;
+		while (__raw_readq(npu->mmio_atsd_regs[reg] + XTS_ATSD_STAT))
+			cpu_relax();
+
+		put_mmio_atsd_reg(npu, reg);
+
+		/*
+		 * The GPU requires two flush ATSDs to ensure all entries have
+		 * been flushed. We use PID 0 as it will never be used for a
+		 * process on the GPU.
+		 */
+		if (flush)
+			mmio_invalidate_pid(npu, 0, true);
+	}
+}
+
 /*
  * Invalidate either a single address or an entire PID depending on
  * the value of va.
  */
 static void mmio_invalidate(struct npu_context *npu_context, int va,
-			unsigned long address)
+			unsigned long address, bool flush)
 {
-	int i, j, reg;
+	int i, j;
 	struct npu *npu;
 	struct pnv_phb *nphb;
 	struct pci_dev *npdev;
-	struct {
-		struct npu *npu;
-		int reg;
-	} mmio_atsd_reg[NV_MAX_NPUS];
+	struct mmio_atsd_reg mmio_atsd_reg[NV_MAX_NPUS];
 	unsigned long pid = npu_context->mm->context.id;
 
 	/*
@@ -525,10 +562,11 @@ static void mmio_invalidate(struct npu_context *npu_context, int va,
 
 			if (va)
 				mmio_atsd_reg[i].reg =
-					mmio_invalidate_va(npu, address, pid);
+					mmio_invalidate_va(npu, address, pid,
+							flush);
 			else
 				mmio_atsd_reg[i].reg =
-					mmio_invalidate_pid(npu, pid);
+					mmio_invalidate_pid(npu, pid, flush);
 
 			/*
 			 * The NPU hardware forwards the shootdown to all GPUs
@@ -544,18 +582,10 @@ static void mmio_invalidate(struct npu_context *npu_context, int va,
 	 */
 	flush_tlb_mm(npu_context->mm);
 
-	/* Wait for all invalidations to complete */
-	for (i = 0; i <= max_npu2_index; i++) {
-		if (mmio_atsd_reg[i].reg < 0)
-			continue;
-
-		/* Wait for completion */
-		npu = mmio_atsd_reg[i].npu;
-		reg = mmio_atsd_reg[i].reg;
-		while (__raw_readq(npu->mmio_atsd_regs[reg] + XTS_ATSD_STAT))
-			cpu_relax();
-		put_mmio_atsd_reg(npu, reg);
-	}
+	mmio_invalidate_wait(mmio_atsd_reg, flush);
+	if (flush)
+		/* Wait for the flush to complete */
+		mmio_invalidate_wait(mmio_atsd_reg, false);
 }
 
 static void pnv_npu2_mn_release(struct mmu_notifier *mn,
@@ -571,7 +601,7 @@ static void pnv_npu2_mn_release(struct mmu_notifier *mn,
 	 * There should be no more translation requests for this PID, but we
 	 * need to ensure any entries for it are removed from the TLB.
 	 */
-	mmio_invalidate(npu_context, 0, 0);
+	mmio_invalidate(npu_context, 0, 0, true);
 }
 
 static void pnv_npu2_mn_change_pte(struct mmu_notifier *mn,
@@ -581,7 +611,7 @@ static void pnv_npu2_mn_change_pte(struct mmu_notifier *mn,
 {
 	struct npu_context *npu_context = mn_to_npu_context(mn);
 
-	mmio_invalidate(npu_context, 1, address);
+	mmio_invalidate(npu_context, 1, address, true);
 }
 
 static void pnv_npu2_mn_invalidate_page(struct mmu_notifier *mn,
@@ -590,7 +620,7 @@ static void pnv_npu2_mn_invalidate_page(struct mmu_notifier *mn,
 {
 	struct npu_context *npu_context = mn_to_npu_context(mn);
 
-	mmio_invalidate(npu_context, 1, address);
+	mmio_invalidate(npu_context, 1, address, true);
 }
 
 static void pnv_npu2_mn_invalidate_range(struct mmu_notifier *mn,
@@ -600,8 +630,11 @@ static void pnv_npu2_mn_invalidate_range(struct mmu_notifier *mn,
 	struct npu_context *npu_context = mn_to_npu_context(mn);
 	unsigned long address;
 
-	for (address = start; address <= end; address += PAGE_SIZE)
-		mmio_invalidate(npu_context, 1, address);
+	for (address = start; address < end; address += PAGE_SIZE)
+		mmio_invalidate(npu_context, 1, address, false);
+
+	/* Do the flush only on the final addess == end */
+	mmio_invalidate(npu_context, 1, address, true);
 }
 
 static const struct mmu_notifier_ops nv_nmmu_notifier_ops = {
@@ -651,8 +684,11 @@ struct npu_context *pnv_npu2_init_context(struct pci_dev *gpdev,
 		/* No nvlink associated with this GPU device */
 		return ERR_PTR(-ENODEV);
 
-	if (!mm) {
-		/* kernel thread contexts are not supported */
+	if (!mm || mm->context.id == 0) {
+		/*
+		 * Kernel thread contexts are not supported and context id 0 is
+		 * reserved on the GPU.
+		 */
 		return ERR_PTR(-EINVAL);
 	}