linux-kernel - Re: [PATCH v2] kvm: iommu: Add cond_resched to legacy device assignment code

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Date:	Tue, 27 Jan 2015 21:31:26 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Joerg Roedel <joro@...tes.org>, Gleb Natapov <gleb@...nel.org>
CC:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org, jroedel@...e.de
Subject: Re: [PATCH v2] kvm: iommu: Add cond_resched to legacy device assignment
 code



On 27/01/2015 11:57, 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>
> ---
>  arch/x86/kvm/iommu.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/iommu.c b/arch/x86/kvm/iommu.c
> index 17b73ee..7dbced3 100644
> --- a/arch/x86/kvm/iommu.c
> +++ b/arch/x86/kvm/iommu.c
> @@ -138,7 +138,7 @@ int kvm_iommu_map_pages(struct kvm *kvm, struct kvm_memory_slot *slot)
>  
>  		gfn += page_size >> PAGE_SHIFT;
>  
> -
> +		cond_resched();
>  	}
>  
>  	return 0;
> @@ -306,6 +306,8 @@ static void kvm_iommu_put_pages(struct kvm *kvm,
>  		kvm_unpin_pages(kvm, pfn, unmap_pages);
>  
>  		gfn += unmap_pages;
> +
> +		cond_resched();
>  	}
>  }
>  
> 

Applying to kvm/queue, thanks.

Paolo
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