linux-kernel - Re: [PATCH 3/2] vfio: Provide module option to disable vfio_iommu

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Message-ID: <20130528164214.GC6073@phenom.dumpdata.com>
Date:	Tue, 28 May 2013 12:42:14 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	kvm@...r.kernel.org, qemu-devel@...gnu.org,
	linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
	chegu_vinod@...com
Subject: Re: [PATCH 3/2] vfio: Provide module option to disable
 vfio_iommu_type1 hugepage support

On Tue, May 28, 2013 at 10:27:52AM -0600, Alex Williamson wrote:
> Add a module option to vfio_iommu_type1 to disable IOMMU hugepage
> support.  This causes iommu_map to only be called with single page
> mappings, disabling the IOMMU driver's ability to use hugepages.
> This option can be enabled by loading vfio_iommu_type1 with
> disable_hugepages=1 or dynamically through sysfs.  If enabled
> dynamically, only new mappings are restricted.
> 
> Signed-off-by: Alex Williamson <alex.williamson@...hat.com>

Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> ---

> 
> As suggested by Konrad.  This is cleaner to add as a follow-on
> 
>  drivers/vfio/vfio_iommu_type1.c |   11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 6654a7e..8a2be4e 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -48,6 +48,12 @@ module_param_named(allow_unsafe_interrupts,
>  MODULE_PARM_DESC(allow_unsafe_interrupts,
>  		 "Enable VFIO IOMMU support for on platforms without interrupt remapping support.");
>  
> +static bool disable_hugepages;
> +module_param_named(disable_hugepages,
> +		   disable_hugepages, bool, S_IRUGO | S_IWUSR);
> +MODULE_PARM_DESC(disable_hugepages,
> +		 "Disable VFIO IOMMU support for IOMMU hugepages.");
> +
>  struct vfio_iommu {
>  	struct iommu_domain	*domain;
>  	struct mutex		lock;
> @@ -270,6 +276,11 @@ static long vfio_pin_pages(unsigned long vaddr, long npage,
>  		return -ENOMEM;
>  	}
>  
> +	if (unlikely(disable_hugepages)) {
> +		vfio_lock_acct(1);
> +		return 1;
> +	}
> +
>  	/* Lock all the consecutive pages from pfn_base */
>  	for (i = 1, vaddr += PAGE_SIZE; i < npage; i++, vaddr += PAGE_SIZE) {
>  		unsigned long pfn = 0;
> 
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