Re: [PATCH] kvm: iommu: Add cond_resched to legacy device assignment code

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On 2014/12/16 23:47, Joerg Roedel wrote:
From: Joerg Roedel <jroedel@xxxxxxx>

When assigning devices to large memory guests (>=128GB guest
memory in the failure case) the functions to create the
IOMMU page-tables for the whole guest might run for a very
long time. On non-preemptible kernels this might cause
Soft-Lockup warnings. Fix these by adding a cond_resched()
to the mapping and unmapping loops.

Signed-off-by: Joerg Roedel <jroedel@xxxxxxx>
---
  virt/kvm/iommu.c | 4 +++-
  1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/virt/kvm/iommu.c b/virt/kvm/iommu.c
index c1e6ae9..ac427e8 100644
--- a/virt/kvm/iommu.c
+++ b/virt/kvm/iommu.c

This file is already gone after one latest commit c274e03af705, "kvm: x86: move assigned-dev.c and iommu.c to arch/x86/" is introduced, so you need to pull your tree firstly :)

Tiejun


@@ -137,7 +137,7 @@ int kvm_iommu_map_pages(struct kvm *kvm, struct kvm_memory_slot *slot)

  		gfn += page_size >> PAGE_SHIFT;

-
+		cond_resched();
  	}

  	return 0;
@@ -311,6 +311,8 @@ static void kvm_iommu_put_pages(struct kvm *kvm,
  		kvm_unpin_pages(kvm, pfn, unmap_pages);

  		gfn += unmap_pages;
+
+		cond_resched();
  	}
  }


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