linux-kernel - Re: [PATCH 1/2] vfio/type1: Adopt fast IOTLB flush interface when unmap IOVAs

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Message-ID: <20171117145152.41fae930@t450s.home>
Date:   Fri, 17 Nov 2017 14:51:52 -0700
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
Cc:     linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        joro@...tes.org, jroedel@...e.de
Subject: Re: [PATCH 1/2] vfio/type1: Adopt fast IOTLB flush interface when
 unmap IOVAs

On Fri, 17 Nov 2017 15:11:19 -0600
Suravee Suthikulpanit <Suravee.Suthikulpanit@....com> wrote:

> From: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
> 
> VFIO IOMMU type1 currently upmaps IOVA pages synchronously, which requires
> IOTLB flushing for every unmapping. This results in large IOTLB flushing
> overhead when handling pass-through devices with a large number of mapped
> IOVAs (e.g. GPUs).

Of course the type of device is really irrelevant, QEMU maps the entire
VM address space for any assigned device.

> This can be avoided by using the new IOTLB flushing interface.
> 
> Cc: Alex Williamson <alex.williamson@...hat.com>
> Cc: Joerg Roedel <jroedel@...e.de>
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
> ---
>  drivers/vfio/vfio_iommu_type1.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 92155cc..28a7ab6 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -698,10 +698,12 @@ static long vfio_unmap_unpin(struct vfio_iommu *iommu, struct vfio_dma *dma,
>  				break;
>  		}
>  
> -		unmapped = iommu_unmap(domain->domain, iova, len);
> +		unmapped = iommu_unmap_fast(domain->domain, iova, len);
>  		if (WARN_ON(!unmapped))
>  			break;
>  
> +		iommu_tlb_range_add(domain->domain, iova, len);
> +

We should only add @unmapped, not @len, right?

>  		unlocked += vfio_unpin_pages_remote(dma, iova,
>  						    phys >> PAGE_SHIFT,
>  						    unmapped >> PAGE_SHIFT,
> @@ -710,6 +712,7 @@ static long vfio_unmap_unpin(struct vfio_iommu *iommu, struct vfio_dma *dma,
>  
>  		cond_resched();
>  	}
> +	iommu_tlb_sync(domain->domain);
>  
>  	dma->iommu_mapped = false;
>  	if (do_accounting) {
> @@ -884,8 +887,11 @@ static int map_try_harder(struct vfio_domain *domain, dma_addr_t iova,
>  			break;
>  	}
>  
> -	for (; i < npage && i > 0; i--, iova -= PAGE_SIZE)
> -		iommu_unmap(domain->domain, iova, PAGE_SIZE);
> +	for (; i < npage && i > 0; i--, iova -= PAGE_SIZE) {
> +		iommu_unmap_fast(domain->domain, iova, PAGE_SIZE);
> +		iommu_tlb_range_add(domain->domain, iova, PAGE_SIZE);
> +	}
> +	iommu_tlb_sync(domain->domain);
>  
>  	return ret;
>  }