[PATCH] vfio/type1: conditional rescheduling while pinning

[Keith Busch <kbusch@meta.com>]

From: Keith Busch <kbusch@kernel.org>

A large DMA mapping request can loop through dma address pinning for
many pages. The repeated vmf_insert_pfn can be costly, so let the task
reschedule as need to prevent CPU stalls.

 rcu: INFO: rcu_sched self-detected stall on CPU
 rcu: 	36-....: (20999 ticks this GP) idle=b01c/1/0x4000000000000000 softirq=35839/35839 fqs=3538
 rcu: 	         hardirqs   softirqs   csw/system
 rcu: 	 number:        0        107            0
 rcu: 	cputime:       50          0        10446   ==> 10556(ms)
 rcu: 	(t=21075 jiffies g=377761 q=204059 ncpus=384)
...
  <TASK>
  ? asm_sysvec_apic_timer_interrupt+0x16/0x20
  ? walk_system_ram_range+0x63/0x120
  ? walk_system_ram_range+0x46/0x120
  ? pgprot_writethrough+0x20/0x20
  lookup_memtype+0x67/0xf0
  track_pfn_insert+0x20/0x40
  vmf_insert_pfn_prot+0x88/0x140
  vfio_pci_mmap_huge_fault+0xf9/0x1b0 [vfio_pci_core]
  __do_fault+0x28/0x1b0
  handle_mm_fault+0xef1/0x2560
  fixup_user_fault+0xf5/0x270
  vaddr_get_pfns+0x169/0x2f0 [vfio_iommu_type1]
  vfio_pin_pages_remote+0x162/0x8e0 [vfio_iommu_type1]
  vfio_iommu_type1_ioctl+0x1121/0x1810 [vfio_iommu_type1]
  ? futex_wake+0x1c1/0x260
  x64_sys_call+0x234/0x17a0
  do_syscall_64+0x63/0x130
  ? exc_page_fault+0x63/0x130
  entry_SYSCALL_64_after_hwframe+0x4b/0x53

Signed-off-by: Keith Busch <kbusch@kernel.org>
---
 drivers/vfio/vfio_iommu_type1.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 50ebc9593c9d7..9ad5fcc2de7c7 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -679,6 +679,7 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr,
 
 		if (unlikely(disable_hugepages))
 			break;
+		cond_resched();
 	}
 
 out:
-- 
2.47.1