powerpc/powernv/ioda2: Allocate TCE table levels on demand for default DMA window

We allocate only the first level of multilevel TCE tables for KVM
already (alloc_userspace_copy==true), and the rest is allocated on demand.
This is not enabled though for bare metal.

This removes the KVM limitation (implicit, via the alloc_userspace_copy
parameter) and always allocates just the first level. The on-demand
allocation of missing levels is already implemented.

As from now on DMA map might happen with disabled interrupts, this
allocates TCEs with GFP_ATOMIC; otherwise lockdep reports errors 1].
In practice just a single page is allocated there so chances for failure
are quite low.

To save time when creating a new clean table, this skips non-allocated
indirect TCE entries in pnv_tce_free just like we already do in
the VFIO IOMMU TCE driver.

This changes the default level number from 1 to 2 to reduce the amount
of memory required for the default 32bit DMA window at the boot time.
The default window size is up to 2GB which requires 4MB of TCEs which is
unlikely to be used entirely or at all as most devices these days are
64bit capable so by switching to 2 levels by default we save 4032KB of
RAM per a device.

While at this, add __GFP_NOWARN to alloc_pages_node() as the userspace
can trigger this path via VFIO, see the failure and try creating a table
again with different parameters which might succeed.

[1]:
===
BUG: sleeping function called from invalid context at mm/page_alloc.c:4596
in_atomic(): 1, irqs_disabled(): 1, pid: 1038, name: scsi_eh_1
2 locks held by scsi_eh_1/1038:
 #0: 000000005efd659a (&host->eh_mutex){+.+.}, at: ata_eh_acquire+0x34/0x80
 #1: 0000000006cf56a6 (&(&host->lock)->rlock){....}, at: ata_exec_internal_sg+0xb0/0x5c0
irq event stamp: 500
hardirqs last  enabled at (499): [<c000000000cb8a74>] _raw_spin_unlock_irqrestore+0x94/0xd0
hardirqs last disabled at (500): [<c000000000cb85c4>] _raw_spin_lock_irqsave+0x44/0x120
softirqs last  enabled at (0): [<c000000000101120>] copy_process.isra.4.part.5+0x640/0x1a80
softirqs last disabled at (0): [<0000000000000000>] 0x0
CPU: 73 PID: 1038 Comm: scsi_eh_1 Not tainted 5.2.0-rc6-le_nv2_aikATfstn1-p1 #634
Call Trace:
[c000003d064cef50] [c000000000c8e6c4] dump_stack+0xe8/0x164 (unreliable)
[c000003d064cefa0] [c00000000014ed78] ___might_sleep+0x2f8/0x310
[c000003d064cf020] [c0000000003ca084] __alloc_pages_nodemask+0x2a4/0x1560
[c000003d064cf220] [c0000000000c2530] pnv_alloc_tce_level.isra.0+0x90/0x130
[c000003d064cf290] [c0000000000c2888] pnv_tce+0x128/0x3b0
[c000003d064cf360] [c0000000000c2c00] pnv_tce_build+0xb0/0xf0
[c000003d064cf3c0] [c0000000000bbd9c] pnv_ioda2_tce_build+0x3c/0xb0
[c000003d064cf400] [c00000000004cfe0] ppc_iommu_map_sg+0x210/0x550
[c000003d064cf510] [c00000000004b7a4] dma_iommu_map_sg+0x74/0xb0
[c000003d064cf530] [c000000000863944] ata_qc_issue+0x134/0x470
[c000003d064cf5b0] [c000000000863ec4] ata_exec_internal_sg+0x244/0x5c0
[c000003d064cf700] [c0000000008642d0] ata_exec_internal+0x90/0xe0
[c000003d064cf780] [c0000000008650ac] ata_dev_read_id+0x2ec/0x640
[c000003d064cf8d0] [c000000000878e28] ata_eh_recover+0x948/0x16d0
[c000003d064cfa10] [c00000000087d760] sata_pmp_error_handler+0x480/0xbf0
[c000003d064cfbc0] [c000000000884624] ahci_error_handler+0x74/0xe0
[c000003d064cfbf0] [c000000000879fa8] ata_scsi_port_error_handler+0x2d8/0x7c0
[c000003d064cfca0] [c00000000087a544] ata_scsi_error+0xb4/0x100
[c000003d064cfd00] [c000000000802450] scsi_error_handler+0x120/0x510
[c000003d064cfdb0] [c000000000140c48] kthread+0x1b8/0x1c0
[c000003d064cfe20] [c00000000000bd8c] ret_from_kernel_thread+0x5c/0x70
ata1: SATA link up 6.0 Gbps (SStatus 133 SControl 300)
irq event stamp: 2305

========================================================
hardirqs last  enabled at (2305): [<c00000000000e4c8>] fast_exc_return_irq+0x28/0x34
hardirqs last disabled at (2303): [<c000000000cb9fd0>] __do_softirq+0x4a0/0x654
WARNING: possible irq lock inversion dependency detected
5.2.0-rc6-le_nv2_aikATfstn1-p1 #634 Tainted: G        W
softirqs last  enabled at (2304): [<c000000000cba054>] __do_softirq+0x524/0x654
softirqs last disabled at (2297): [<c00000000010f278>] irq_exit+0x128/0x180
--------------------------------------------------------
swapper/0/0 just changed the state of lock:
0000000006cf56a6 (&(&host->lock)->rlock){-...}, at: ahci_single_level_irq_intr+0xac/0x120
but this lock took another, HARDIRQ-unsafe lock in the past:
 (fs_reclaim){+.+.}

and interrupts could create inverse lock ordering between them.

other info that might help us debug this:
 Possible interrupt unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(fs_reclaim);
                               local_irq_disable();
                               lock(&(&host->lock)->rlock);
                               lock(fs_reclaim);
  <Interrupt>
    lock(&(&host->lock)->rlock);

 *** DEADLOCK ***

no locks held by swapper/0/0.

the shortest dependencies between 2nd lock and 1st lock:
 -> (fs_reclaim){+.+.} ops: 167579 {
    HARDIRQ-ON-W at:
                      lock_acquire+0xf8/0x2a0
                      fs_reclaim_acquire.part.23+0x44/0x60
                      kmem_cache_alloc_node_trace+0x80/0x590
                      alloc_desc+0x64/0x270
                      __irq_alloc_descs+0x2e4/0x3a0
                      irq_domain_alloc_descs+0xb0/0x150
                      irq_create_mapping+0x168/0x2c0
                      xics_smp_probe+0x2c/0x98
                      pnv_smp_probe+0x40/0x9c
                      smp_prepare_cpus+0x524/0x6c4
                      kernel_init_freeable+0x1b4/0x650
                      kernel_init+0x2c/0x148
                      ret_from_kernel_thread+0x5c/0x70
    SOFTIRQ-ON-W at:
                      lock_acquire+0xf8/0x2a0
                      fs_reclaim_acquire.part.23+0x44/0x60
                      kmem_cache_alloc_node_trace+0x80/0x590
                      alloc_desc+0x64/0x270
                      __irq_alloc_descs+0x2e4/0x3a0
                      irq_domain_alloc_descs+0xb0/0x150
                      irq_create_mapping+0x168/0x2c0
                      xics_smp_probe+0x2c/0x98
                      pnv_smp_probe+0x40/0x9c
                      smp_prepare_cpus+0x524/0x6c4
                      kernel_init_freeable+0x1b4/0x650
                      kernel_init+0x2c/0x148
                      ret_from_kernel_thread+0x5c/0x70
    INITIAL USE at:
                     lock_acquire+0xf8/0x2a0
                     fs_reclaim_acquire.part.23+0x44/0x60
                     kmem_cache_alloc_node_trace+0x80/0x590
                     alloc_desc+0x64/0x270
                     __irq_alloc_descs+0x2e4/0x3a0
                     irq_domain_alloc_descs+0xb0/0x150
                     irq_create_mapping+0x168/0x2c0
                     xics_smp_probe+0x2c/0x98
                     pnv_smp_probe+0x40/0x9c
                     smp_prepare_cpus+0x524/0x6c4
                     kernel_init_freeable+0x1b4/0x650
                     kernel_init+0x2c/0x148
                     ret_from_kernel_thread+0x5c/0x70
  }
===
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: Alistair Popple <alistair@popple.id.au>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20190718051139.74787-4-aik@ozlabs.ru

arch/powerpc/platforms/powernv/pci-ioda-tce.c

@@ -36,7 +36,8 @@ static __be64 *pnv_alloc_tce_level(int nid, unsigned int shift)
 	struct page *tce_mem = NULL;
 	__be64 *addr;
 
-	tce_mem = alloc_pages_node(nid, GFP_KERNEL, shift - PAGE_SHIFT);
+	tce_mem = alloc_pages_node(nid, GFP_ATOMIC | __GFP_NOWARN,
+			shift - PAGE_SHIFT);
 	if (!tce_mem) {
 		pr_err("Failed to allocate a TCE memory, level shift=%d\n",
 				shift);
@@ -169,6 +170,9 @@ void pnv_tce_free(struct iommu_table *tbl, long index, long npages)
 
 		if (ptce)
 			*ptce = cpu_to_be64(0);
+		else
+			/* Skip the rest of the level */
+			i |= tbl->it_level_size - 1;
 	}
 }
 
@@ -268,7 +272,6 @@ long pnv_pci_ioda2_table_alloc_pages(int nid, __u64 bus_offset,
 	unsigned int table_shift = max_t(unsigned int, entries_shift + 3,
 			PAGE_SHIFT);
 	const unsigned long tce_table_size = 1UL << table_shift;
-	unsigned int tmplevels = levels;
 
 	if (!levels || (levels > POWERNV_IOMMU_MAX_LEVELS))
 		return -EINVAL;
@@ -276,9 +279,6 @@ long pnv_pci_ioda2_table_alloc_pages(int nid, __u64 bus_offset,
 	if (!is_power_of_2(window_size))
 		return -EINVAL;
 
-	if (alloc_userspace_copy && (window_size > (1ULL << 32)))
-		tmplevels = 1;
-
 	/* Adjust direct table size from window_size and levels */
 	entries_shift = (entries_shift + levels - 1) / levels;
 	level_shift = entries_shift + 3;
@@ -289,7 +289,7 @@ long pnv_pci_ioda2_table_alloc_pages(int nid, __u64 bus_offset,
 
 	/* Allocate TCE table */
 	addr = pnv_pci_ioda2_table_do_alloc_pages(nid, level_shift,
-			tmplevels, tce_table_size, &offset, &total_allocated);
+			1, tce_table_size, &offset, &total_allocated);
 
 	/* addr==NULL means that the first level allocation failed */
 	if (!addr)
@@ -300,18 +300,18 @@ long pnv_pci_ioda2_table_alloc_pages(int nid, __u64 bus_offset,
 	 * we did not allocate as much as we wanted,
 	 * release partially allocated table.
 	 */
-	if (tmplevels == levels && offset < tce_table_size)
+	if (levels == 1 && offset < tce_table_size)
 		goto free_tces_exit;
 
 	/* Allocate userspace view of the TCE table */
 	if (alloc_userspace_copy) {
 		offset = 0;
 		uas = pnv_pci_ioda2_table_do_alloc_pages(nid, level_shift,
-				tmplevels, tce_table_size, &offset,
+				1, tce_table_size, &offset,
 				&total_allocated_uas);
 		if (!uas)
 			goto free_tces_exit;
-		if (tmplevels == levels && (offset < tce_table_size ||
+		if (levels == 1 && (offset < tce_table_size ||
 				total_allocated_uas != total_allocated))
 			goto free_uas_exit;
 	}
@@ -326,7 +326,7 @@ long pnv_pci_ioda2_table_alloc_pages(int nid, __u64 bus_offset,
 
 	pr_debug("Created TCE table: ws=%08llx ts=%lx @%08llx base=%lx uas=%p levels=%d/%d\n",
 			window_size, tce_table_size, bus_offset, tbl->it_base,
-			tbl->it_userspace, tmplevels, levels);
+			tbl->it_userspace, 1, levels);
 
 	return 0;
 

arch/powerpc/platforms/powernv/pci.h

@@ -219,7 +219,7 @@ extern struct iommu_table_group *pnv_npu_compound_attach(
 		struct pnv_ioda_pe *pe);
 
 /* pci-ioda-tce.c */
-#define POWERNV_IOMMU_DEFAULT_LEVELS	1
+#define POWERNV_IOMMU_DEFAULT_LEVELS	2
 #define POWERNV_IOMMU_MAX_LEVELS	5
 
 extern int pnv_tce_build(struct iommu_table *tbl, long index, long npages,