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

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Message-ID: <5490DEB1.30305@intel.com>
Date:	Wed, 17 Dec 2014 09:38:57 +0800
From:	"Chen, Tiejun" <tiejun.chen@...el.com>
To:	Joerg Roedel <joro@...tes.org>, Gleb Natapov <gleb@...nel.org>,
	Paolo Bonzini <pbonzini@...hat.com>
CC:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Joerg Roedel <jroedel@...e.de>
Subject: Re: [PATCH] kvm: iommu: Add cond_resched to legacy device assignment
 code

On 2014/12/16 23:47, Joerg Roedel wrote:
> From: Joerg Roedel <jroedel@...e.de>
>
> 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@...e.de>
> ---
>   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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