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Date: Thu, 10 Aug 2017 09:11:12 -0400
From: Konrad Rzeszutek Wilk <konrad@...nok.org>
To: Tycho Andersen <tycho@...ker.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	kernel-hardening@...ts.openwall.com,
	Marco Benatto <marco.antonio.780@...il.com>,
	Juerg Haefliger <juerg.haefliger@...onical.com>,
	Juerg Haefliger <juerg.haefliger@....com>
Subject: Re: [PATCH v5 08/10] arm64/mm: Add support for XPFO to swiotlb

On Wed, Aug 09, 2017 at 02:07:53PM -0600, Tycho Andersen wrote:
> From: Juerg Haefliger <juerg.haefliger@....com>
> 
> Pages that are unmapped by XPFO need to be mapped before and unmapped
> again after (to restore the original state) the __dma_{map,unmap}_area()
> operations to prevent fatal page faults.
> 
> Signed-off-by: Juerg Haefliger <juerg.haefliger@...onical.com>
> Signed-off-by: Tycho Andersen <tycho@...ker.com>
> ---
>  arch/arm64/include/asm/cacheflush.h | 11 +++++++++
>  arch/arm64/mm/dma-mapping.c         | 32 +++++++++++++-------------
>  arch/arm64/mm/xpfo.c                | 45 +++++++++++++++++++++++++++++++++++++
>  3 files changed, 72 insertions(+), 16 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/cacheflush.h b/arch/arm64/include/asm/cacheflush.h
> index d74a284abdc2..b6a462e3b2f9 100644
> --- a/arch/arm64/include/asm/cacheflush.h
> +++ b/arch/arm64/include/asm/cacheflush.h
> @@ -93,6 +93,17 @@ extern void __dma_map_area(const void *, size_t, int);
>  extern void __dma_unmap_area(const void *, size_t, int);
>  extern void __dma_flush_area(const void *, size_t);
>  
> +#ifdef CONFIG_XPFO
> +#include <linux/xpfo.h>
> +#define _dma_map_area(addr, size, dir) \
> +	xpfo_dma_map_unmap_area(true, addr, size, dir)
> +#define _dma_unmap_area(addr, size, dir) \
> +	xpfo_dma_map_unmap_area(false, addr, size, dir)
> +#else
> +#define _dma_map_area(addr, size, dir) __dma_map_area(addr, size, dir)
> +#define _dma_unmap_area(addr, size, dir) __dma_unmap_area(addr, size, dir)
> +#endif
> +
>  /*
>   * Copy user data from/to a page which is mapped into a different
>   * processes address space.  Really, we want to allow our "user
> diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
> index f27d4dd04384..a79f200786ab 100644
> --- a/arch/arm64/mm/dma-mapping.c
> +++ b/arch/arm64/mm/dma-mapping.c
> @@ -204,7 +204,7 @@ static dma_addr_t __swiotlb_map_page(struct device *dev, struct page *page,
>  	dev_addr = swiotlb_map_page(dev, page, offset, size, dir, attrs);
>  	if (!is_device_dma_coherent(dev) &&
>  	    (attrs & DMA_ATTR_SKIP_CPU_SYNC) == 0)
> -		__dma_map_area(phys_to_virt(dma_to_phys(dev, dev_addr)), size, dir);
> +		_dma_map_area(phys_to_virt(dma_to_phys(dev, dev_addr)), size, dir);
>  
>  	return dev_addr;
>  }
> @@ -216,7 +216,7 @@ static void __swiotlb_unmap_page(struct device *dev, dma_addr_t dev_addr,
>  {
>  	if (!is_device_dma_coherent(dev) &&
>  	    (attrs & DMA_ATTR_SKIP_CPU_SYNC) == 0)
> -		__dma_unmap_area(phys_to_virt(dma_to_phys(dev, dev_addr)), size, dir);
> +		_dma_unmap_area(phys_to_virt(dma_to_phys(dev, dev_addr)), size, dir);
>  	swiotlb_unmap_page(dev, dev_addr, size, dir, attrs);
>  }
>  
> @@ -231,8 +231,8 @@ static int __swiotlb_map_sg_attrs(struct device *dev, struct scatterlist *sgl,
>  	if (!is_device_dma_coherent(dev) &&
>  	    (attrs & DMA_ATTR_SKIP_CPU_SYNC) == 0)
>  		for_each_sg(sgl, sg, ret, i)
> -			__dma_map_area(phys_to_virt(dma_to_phys(dev, sg->dma_address)),
> -				       sg->length, dir);
> +			_dma_map_area(phys_to_virt(dma_to_phys(dev, sg->dma_address)),
> +				      sg->length, dir);
>  
>  	return ret;
>  }
> @@ -248,8 +248,8 @@ static void __swiotlb_unmap_sg_attrs(struct device *dev,
>  	if (!is_device_dma_coherent(dev) &&
>  	    (attrs & DMA_ATTR_SKIP_CPU_SYNC) == 0)
>  		for_each_sg(sgl, sg, nelems, i)
> -			__dma_unmap_area(phys_to_virt(dma_to_phys(dev, sg->dma_address)),
> -					 sg->length, dir);
> +			_dma_unmap_area(phys_to_virt(dma_to_phys(dev, sg->dma_address)),
> +					sg->length, dir);
>  	swiotlb_unmap_sg_attrs(dev, sgl, nelems, dir, attrs);
>  }
>  
> @@ -258,7 +258,7 @@ static void __swiotlb_sync_single_for_cpu(struct device *dev,
>  					  enum dma_data_direction dir)
>  {
>  	if (!is_device_dma_coherent(dev))
> -		__dma_unmap_area(phys_to_virt(dma_to_phys(dev, dev_addr)), size, dir);
> +		_dma_unmap_area(phys_to_virt(dma_to_phys(dev, dev_addr)), size, dir);
>  	swiotlb_sync_single_for_cpu(dev, dev_addr, size, dir);
>  }
>  
> @@ -268,7 +268,7 @@ static void __swiotlb_sync_single_for_device(struct device *dev,
>  {
>  	swiotlb_sync_single_for_device(dev, dev_addr, size, dir);
>  	if (!is_device_dma_coherent(dev))
> -		__dma_map_area(phys_to_virt(dma_to_phys(dev, dev_addr)), size, dir);
> +		_dma_map_area(phys_to_virt(dma_to_phys(dev, dev_addr)), size, dir);
>  }
>  
>  static void __swiotlb_sync_sg_for_cpu(struct device *dev,
> @@ -280,8 +280,8 @@ static void __swiotlb_sync_sg_for_cpu(struct device *dev,
>  
>  	if (!is_device_dma_coherent(dev))
>  		for_each_sg(sgl, sg, nelems, i)
> -			__dma_unmap_area(phys_to_virt(dma_to_phys(dev, sg->dma_address)),
> -					 sg->length, dir);
> +			_dma_unmap_area(phys_to_virt(dma_to_phys(dev, sg->dma_address)),
> +					sg->length, dir);
>  	swiotlb_sync_sg_for_cpu(dev, sgl, nelems, dir);
>  }
>  
> @@ -295,8 +295,8 @@ static void __swiotlb_sync_sg_for_device(struct device *dev,
>  	swiotlb_sync_sg_for_device(dev, sgl, nelems, dir);
>  	if (!is_device_dma_coherent(dev))
>  		for_each_sg(sgl, sg, nelems, i)
> -			__dma_map_area(phys_to_virt(dma_to_phys(dev, sg->dma_address)),
> -				       sg->length, dir);
> +			_dma_map_area(phys_to_virt(dma_to_phys(dev, sg->dma_address)),
> +				      sg->length, dir);
>  }
>  
>  static int __swiotlb_mmap_pfn(struct vm_area_struct *vma,
> @@ -758,7 +758,7 @@ static void __iommu_sync_single_for_cpu(struct device *dev,
>  		return;
>  
>  	phys = iommu_iova_to_phys(iommu_get_domain_for_dev(dev), dev_addr);
> -	__dma_unmap_area(phys_to_virt(phys), size, dir);
> +	_dma_unmap_area(phys_to_virt(phys), size, dir);
>  }
>  
>  static void __iommu_sync_single_for_device(struct device *dev,
> @@ -771,7 +771,7 @@ static void __iommu_sync_single_for_device(struct device *dev,
>  		return;
>  
>  	phys = iommu_iova_to_phys(iommu_get_domain_for_dev(dev), dev_addr);
> -	__dma_map_area(phys_to_virt(phys), size, dir);
> +	_dma_map_area(phys_to_virt(phys), size, dir);
>  }
>  
>  static dma_addr_t __iommu_map_page(struct device *dev, struct page *page,
> @@ -811,7 +811,7 @@ static void __iommu_sync_sg_for_cpu(struct device *dev,
>  		return;
>  
>  	for_each_sg(sgl, sg, nelems, i)
> -		__dma_unmap_area(sg_virt(sg), sg->length, dir);
> +		_dma_unmap_area(sg_virt(sg), sg->length, dir);
>  }
>  
>  static void __iommu_sync_sg_for_device(struct device *dev,
> @@ -825,7 +825,7 @@ static void __iommu_sync_sg_for_device(struct device *dev,
>  		return;
>  
>  	for_each_sg(sgl, sg, nelems, i)
> -		__dma_map_area(sg_virt(sg), sg->length, dir);
> +		_dma_map_area(sg_virt(sg), sg->length, dir);
>  }
>  
>  static int __iommu_map_sg_attrs(struct device *dev, struct scatterlist *sgl,
> diff --git a/arch/arm64/mm/xpfo.c b/arch/arm64/mm/xpfo.c
> index de03a652d48a..c4deb2b720cf 100644
> --- a/arch/arm64/mm/xpfo.c
> +++ b/arch/arm64/mm/xpfo.c
> @@ -11,8 +11,10 @@
>   * the Free Software Foundation.
>   */
>  
> +#include <linux/highmem.h>
>  #include <linux/mm.h>
>  #include <linux/module.h>
> +#include <linux/xpfo.h>
>  
>  #include <asm/tlbflush.h>
>  
> @@ -62,3 +64,46 @@ inline void xpfo_flush_kernel_page(struct page *page, int order)
>  
>  	flush_tlb_kernel_range(kaddr, kaddr + (1 << order) * size);
>  }
> +
> +inline void xpfo_dma_map_unmap_area(bool map, const void *addr, size_t size,

And inline? You sure about that? It is quite a lot of code to duplicate
in all of those call-sites.

> +				    int dir)

Not enum dma_data_direction ?
> +{
> +	unsigned long flags;
> +	struct page *page = virt_to_page(addr);
> +
> +	/*
> +	 * +2 here because we really want
> +	 * ceil(size / PAGE_SIZE), not floor(), and one extra in case things are
> +	 * not page aligned
> +	 */
> +	int i, possible_pages = size / PAGE_SIZE + 2;

Could you use the PAGE_SHIFT macro instead? Or PFN_UP ?

And there is also the PAGE_ALIGN macro...

> +	void *buf[possible_pages];

What if you just did 'void *buf[possible_pages] = { };'

Wouldn't that eliminate the need for the memset?

> +
> +	memset(buf, 0, sizeof(void *) * possible_pages);
> +
> +	local_irq_save(flags);

?? Why?

> +
> +	/* Map the first page */
> +	if (xpfo_page_is_unmapped(page))
> +		buf[0] = kmap_atomic(page);

Especially in context of the lookup and kmap_atomic which can take
a bit of time.
> +
> +	/* Map the remaining pages */
> +	for (i = 1; i < possible_pages; i++) {
> +		if (page_to_virt(page + i) >= addr + size)
> +			break;
> +
> +		if (xpfo_page_is_unmapped(page + i))
> +			buf[i] = kmap_atomic(page + i);
> +	}
> +
> +	if (map)
> +		__dma_map_area(addr, size, dir);
> +	else
> +		__dma_unmap_area(addr, size, dir);
> +
> +	for (i = 0; i < possible_pages; i++)
> +		if (buf[i])
> +			kunmap_atomic(buf[i]);
> +
> +	local_irq_restore(flags);
> +}
> -- 
> 2.11.0
> 

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