6.15-stable review patch. If anyone has any objections, please let me know.
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From: Keith Busch kbusch@kernel.org
[ Upstream commit b1779e4f209c7ff7e32f3c79d69bca4e3a3a68b6 ]
A large DMA mapping request can loop through dma address pinning for many pages. In cases where THP can not be used, the repeated vmf_insert_pfn can be costly, so let the task reschedule as need to prevent CPU stalls. Failure to do so has potential harmful side effects, like increased memory pressure as unrelated rcu tasks are unable to make their reclaim callbacks and result in OOM conditions.
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 Reviewed-by: Paul E. McKenney paulmck@kernel.org Link: https://lore.kernel.org/r/20250715184622.3561598-1-kbusch@meta.com Signed-off-by: Alex Williamson alex.williamson@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/vfio/vfio_iommu_type1.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c index ba5d91e576af..a685e01f73f5 100644 --- a/drivers/vfio/vfio_iommu_type1.c +++ b/drivers/vfio/vfio_iommu_type1.c @@ -648,6 +648,13 @@ static long vfio_pin_pages_remote(struct vfio_dma *dma, unsigned long vaddr,
while (npage) { if (!batch->size) { + /* + * Large mappings may take a while to repeatedly refill + * the batch, so conditionally relinquish the CPU when + * needed to avoid stalls. + */ + cond_resched(); + /* Empty batch, so refill it. */ ret = vaddr_get_pfns(mm, vaddr, npage, dma->prot, &pfn, batch);