Re: [PATCH v6 4/7] dma-reserved-iommu: alloc/free_reserved_iova_domain

[Alex Williamson]

On Mon,  4 Apr 2016 08:06:59 +0000
Eric Auger <eric.auger@xxxxxxxxxx> wrote:

> Introduce alloc/free_reserved_iova_domain in the IOMMU API.
> alloc_reserved_iova_domain initializes an iova domain at a given
> iova base address and with a given size. This iova domain will
> be used to allocate iova within that window. Those IOVAs will be reserved
> for special purpose, typically MSI frame binding. Allocation function
> within the reserved iova domain will be introduced in subsequent patches.
> 
> Those functions are implemented and exposed if CONFIG_IOMMU_DMA_RESERVED
> is seta.
> 
> Signed-off-by: Eric Auger <eric.auger@xxxxxxxxxx>
> 
> ---
> 
> v5 -> v6:
> - use spin lock instead of mutex
> 
> v3 -> v4:
> - formerly in "iommu/arm-smmu: implement alloc/free_reserved_iova_domain" &
>   "iommu: add alloc/free_reserved_iova_domain"
> 
> v2 -> v3:
> - remove iommu_alloc_reserved_iova_domain & iommu_free_reserved_iova_domain
>   static implementation in case CONFIG_IOMMU_API is not set
> 
> v1 -> v2:
> - moved from vfio API to IOMMU API
> ---
>  drivers/iommu/Kconfig              |  8 ++++
>  drivers/iommu/Makefile             |  1 +
>  drivers/iommu/dma-reserved-iommu.c | 75 ++++++++++++++++++++++++++++++++++++++
>  include/linux/dma-reserved-iommu.h | 45 +++++++++++++++++++++++
>  4 files changed, 129 insertions(+)
>  create mode 100644 drivers/iommu/dma-reserved-iommu.c
>  create mode 100644 include/linux/dma-reserved-iommu.h
> 
> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> index dd1dc39..a5a1530 100644
> --- a/drivers/iommu/Kconfig
> +++ b/drivers/iommu/Kconfig
> @@ -74,6 +74,12 @@ config IOMMU_DMA
>  	select IOMMU_IOVA
>  	select NEED_SG_DMA_LENGTH
>  
> +# IOMMU reserved IOVA mapping (MSI doorbell)
> +config IOMMU_DMA_RESERVED
> +	bool
> +	select IOMMU_API
> +	select IOMMU_IOVA
> +
>  config FSL_PAMU
>  	bool "Freescale IOMMU support"
>  	depends on PPC32
> @@ -307,6 +313,7 @@ config SPAPR_TCE_IOMMU
>  config ARM_SMMU
>  	bool "ARM Ltd. System MMU (SMMU) Support"
>  	depends on (ARM64 || ARM) && MMU
> +	select IOMMU_DMA_RESERVED
>  	select IOMMU_API
>  	select IOMMU_IO_PGTABLE_LPAE
>  	select ARM_DMA_USE_IOMMU if ARM
> @@ -320,6 +327,7 @@ config ARM_SMMU
>  config ARM_SMMU_V3
>  	bool "ARM Ltd. System MMU Version 3 (SMMUv3) Support"
>  	depends on ARM64 && PCI
> +	select IOMMU_DMA_RESERVED
>  	select IOMMU_API
>  	select IOMMU_IO_PGTABLE_LPAE
>  	select GENERIC_MSI_IRQ_DOMAIN
> diff --git a/drivers/iommu/Makefile b/drivers/iommu/Makefile
> index c6edb31..6c9ae99 100644
> --- a/drivers/iommu/Makefile
> +++ b/drivers/iommu/Makefile
> @@ -2,6 +2,7 @@ obj-$(CONFIG_IOMMU_API) += iommu.o
>  obj-$(CONFIG_IOMMU_API) += iommu-traces.o
>  obj-$(CONFIG_IOMMU_API) += iommu-sysfs.o
>  obj-$(CONFIG_IOMMU_DMA) += dma-iommu.o
> +obj-$(CONFIG_IOMMU_DMA_RESERVED) += dma-reserved-iommu.o
>  obj-$(CONFIG_IOMMU_IO_PGTABLE) += io-pgtable.o
>  obj-$(CONFIG_IOMMU_IO_PGTABLE_ARMV7S) += io-pgtable-arm-v7s.o
>  obj-$(CONFIG_IOMMU_IO_PGTABLE_LPAE) += io-pgtable-arm.o
> diff --git a/drivers/iommu/dma-reserved-iommu.c b/drivers/iommu/dma-reserved-iommu.c
> new file mode 100644
> index 0000000..a461482
> --- /dev/null
> +++ b/drivers/iommu/dma-reserved-iommu.c
> @@ -0,0 +1,75 @@
> +/*
> + * Reserved IOVA Management
> + *
> + * Copyright (c) 2015 Linaro Ltd.
> + *              www.linaro.org
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + */
> +
> +#include <linux/iommu.h>
> +#include <linux/iova.h>
> +
> +int iommu_alloc_reserved_iova_domain(struct iommu_domain *domain,
> +				     dma_addr_t iova, size_t size,
> +				     unsigned long order)
> +{
> +	unsigned long granule, mask;
> +	struct iova_domain *iovad;
> +	unsigned long flags;
> +	int ret = 0;
> +
> +	granule = 1UL << order;
> +	mask = granule - 1;
> +	if (iova & mask || (!size) || (size & mask))
> +		return -EINVAL;
> +
> +	iovad = kzalloc(sizeof(struct iova_domain), GFP_KERNEL);
> +	if (!iovad)
> +		return -ENOMEM;
> +
> +	spin_lock_irqsave(&domain->reserved_lock, flags);
> +
> +	if (domain->reserved_iova_cookie) {
> +		ret = -EEXIST;
> +		goto free_unlock;
> +	}
> +
> +	init_iova_domain(iovad, granule,
> +			 iova >> order, (iova + size - 1) >> order);
> +	domain->reserved_iova_cookie = iovad;
> +	goto unlock;
> +
> +free_unlock:
> +	kfree(iovad);
> +unlock:
> +	spin_unlock_irqrestore(&domain->reserved_lock, flags);
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(iommu_alloc_reserved_iova_domain);
> +
> +void iommu_free_reserved_iova_domain(struct iommu_domain *domain)
> +{
> +	struct iova_domain *iovad =
> +		(struct iova_domain *)domain->reserved_iova_cookie;
> +	unsigned long flags;
> +
> +	if (!iovad)
> +		return;
> +
> +	spin_lock_irqsave(&domain->reserved_lock, flags);
> +
> +	put_iova_domain(iovad);
> +	kfree(iovad);
> +
> +	spin_unlock_irqrestore(&domain->reserved_lock, flags);
> +}

The locking here looks wrong, reserved_iova_cookie needs to be read and
cleared (currently missing) within the lock, the put and free can
probably happen outside the lock.  Likewise the init_iova_domain() in
the alloc path probably doesn't need to iccur under spinlock, but
testing and setting reserved_iova_cookie does.  Seems like a mutex
would do for locking here, but maybe the rb-tree manipulation has
reasons for using a spinlock.  Thanks,

Alex

> +EXPORT_SYMBOL_GPL(iommu_free_reserved_iova_domain);
> diff --git a/include/linux/dma-reserved-iommu.h b/include/linux/dma-reserved-iommu.h
> new file mode 100644
> index 0000000..5bf863b
> --- /dev/null
> +++ b/include/linux/dma-reserved-iommu.h
> @@ -0,0 +1,45 @@
> +/*
> + * Copyright (c) 2015 Linaro Ltd.
> + *              www.linaro.org
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + */
> +#ifndef __DMA_RESERVED_IOMMU_H
> +#define __DMA_RESERVED_IOMMU_H
> +
> +#ifdef __KERNEL__
> +#include <asm/errno.h>
> +
> +#ifdef CONFIG_IOMMU_DMA_RESERVED
> +#include <linux/iommu.h>
> +
> +/**
> + * iommu_alloc_reserved_iova_domain: allocate the reserved iova domain
> + *
> + * @domain: iommu domain handle
> + * @iova: base iova address
> + * @size: iova window size
> + * @order: page order
> + */
> +int iommu_alloc_reserved_iova_domain(struct iommu_domain *domain,
> +				     dma_addr_t iova, size_t size,
> +				     unsigned long order);
> +
> +/**
> + * iommu_free_reserved_iova_domain: free the reserved iova domain
> + *
> + * @domain: iommu domain handle
> + */
> +void iommu_free_reserved_iova_domain(struct iommu_domain *domain);
> +
> +#endif	/* CONFIG_IOMMU_DMA_RESERVED */
> +#endif	/* __KERNEL__ */
> +#endif	/* __DMA_RESERVED_IOMMU_H */