Date:	Tue, 24 Jul 2012 20:48:46 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Shuah Khan <shuah.khan@...com>
Cc:	fujita.tomonori@....ntt.co.jp, akpm@...ux-foundation.org,
	paul.gortmaker@...driver.com, bhelgaas@...gle.com,
	amwang@...hat.com, rob@...dley.net, linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org, shuahkhan@...il.com
Subject: Re: [PATCH RESEND] swiotlb: Disable swiotlb overflow support when
 CONFIG_ISA is disabled

On Tue, Jul 24, 2012 at 01:46:27PM -0600, Shuah Khan wrote:
> Disable iotlb overflow support when CONFIG_ISA is disabled. Add deprecation

You need to check one more thing. In the email I mentioned that the bulk
of the drivers that utilize this are ISA, but there are also some that
are PCI dependent.

So I grepped for anything that does 'dma_map_page' and some of them are
even PCIe, for example: drivers/net/ethernet/intel/ixgbevf/ixgbevf_main.c

Which means that the check for CONFIG_ISA is not sufficient.

> notice warning message and deprecation schedule documentation. This is the
> first step towards removing overflow support, to be consistent with other
> iommu implementations and return DMA_ERROR_CODE. This disabling step is for
> finding drivers that don't call dma_mapping_error to check for errors returned
> by the mapping interface. Once drivers are fixed overflow support can be
> removed.
> 
> Signed-off-by: Shuah Khan <shuah.khan@...com>

Did you do a cross compile on IA64 just to double check? Comments below.

> ---
>  Documentation/feature-removal-schedule.txt |   22 ++++++--
>  lib/swiotlb.c                              |   79 +++++++++++++++++++++-------
>  2 files changed, 79 insertions(+), 22 deletions(-)
> 
> diff --git a/Documentation/feature-removal-schedule.txt b/Documentation/feature-removal-schedule.txt
> index 5979c3e..ce6c0ae 100644
> --- a/Documentation/feature-removal-schedule.txt
> +++ b/Documentation/feature-removal-schedule.txt
> @@ -35,7 +35,7 @@ What:	x86_32 "no-hlt" cmdline param
>  When:	2012
>  Why:	remove a branch from idle path, simplify code used by everybody.
>  	This option disabled the use of HLT in idle and machine_halt()
> -	for hardware that was flakey 15-years ago.  Today we have
> +	for hardware that was flaky 15-years ago.  Today we have

Ummm, that is not part of what this patch should be doing.

>  	"idle=poll" that removed HLT from idle, and so if such a machine
>  	is still running the upstream kernel, "idle=poll" is likely sufficient.
>  Who:	Len Brown <len.brown@...el.com>
> @@ -160,7 +160,7 @@ Files:	arch/*/kernel/*_ksyms.c
>  Check:	kernel_thread
>  Why:	kernel_thread is a low-level implementation detail.  Drivers should
>          use the <linux/kthread.h> API instead which shields them from
> -	implementation details and provides a higherlevel interface that
> +	implementation details and provides a higher level interface that

Neither is this.
>  	prevents bugs and code duplication
>  Who:	Christoph Hellwig <hch@....de>
>  
> @@ -236,7 +236,7 @@ Who:	David Brownell <dbrownell@...rs.sourceforge.net>
>  
>  What:	b43 support for firmware revision < 410
>  When:	The schedule was July 2008, but it was decided that we are going to keep the
> -        code as long as there are no major maintanance headaches.
> +        code as long as there are no major maintenance headaches.

Or this.

>  	So it _could_ be removed _any_ time now, if it conflicts with something new.
>  Why:	The support code for the old firmware hurts code readability/maintainability
>  	and slightly hurts runtime performance. Bugfixes for the old firmware
> @@ -608,3 +608,19 @@ When:	June 2013
>  Why:	Unsupported/unmaintained/unused since 2.6
>  
>  ----------------------------
> +
> +What:	SWIOTLB overflow buffer support.
> +When:	3.8
> +Why:	Remove SWIOTLB overflow buffer support and return DMA_ERROR_CODE
> +	(a value of zero) to make it consistent with iommu implementation
> +	on Intel, AMD, and swiotlb-xen. In 3.6, Disable iotlb overflow
> +	support when CONFIG_ISA is disabled with the intent to find drivers
> +	that don't call dma_mapping_error to check for errors returned by the
> +	mapping interface. Once drivers are fixed overflow support can be
> +	removed.
> +	If you see any problems related to disabling SWIOTLB overflow buffer,
> +	please report to us!
> +	E-mail us at: linux-kernel@...r.kernel.org
> +Who:	Shuah Khan <shuah.khan@...com> <shuahkhan@...il.com>
> +
> +----------------------------
> diff --git a/lib/swiotlb.c b/lib/swiotlb.c
> index 45bc1f8..0123bb8 100644
> --- a/lib/swiotlb.c
> +++ b/lib/swiotlb.c
> @@ -15,6 +15,9 @@
>   * 05/09/10 linville	Add support for syncing ranges, support syncing for
>   *			DMA_BIDIRECTIONAL mappings, miscellaneous cleanup.
>   * 08/12/11 beckyb	Add highmem support
> + * 07/2012  shuahkhan	Disable iotlb overflow support when CONFIG_ISA
> + *			is enabled. Remove it for all configs when drivers
> + *			that don't check for mapping errors are fixed.

Don't bother. The changelog is now in the git commit.

>   */
>  
>  #include <linux/cache.h>
> @@ -68,7 +71,11 @@ static unsigned long io_tlb_nslabs;
>  /*
>   * When the IOMMU overflows we return a fallback buffer. This sets the size.
>   */
> +#if defined(CONFIG_ISA)
>  static unsigned long io_tlb_overflow = 32*1024;
> +#else
> +static unsigned long io_tlb_overflow;
> +#endif
>  
>  static void *io_tlb_overflow_buffer;
>  
> @@ -92,6 +99,24 @@ static DEFINE_SPINLOCK(io_tlb_lock);
>  
>  static int late_alloc;
>  
> +static void swiotlb_print_overflow_deprecation_notice(void)
> +{
> +	if (io_tlb_overflow) {
> +		pr_warn("SWIOTLB overflow buffer will be deprecated.\n"
> +			"  If you have a driver that depends on this feature\n"
> +			"  please Email us at: linux-kernel@...r.kernel.org,\n"
> +			"  Shuah Khan (shuahkhan@...il.com), and\n"
> +			"  Konrad Wilk (konrad.wilk@...cle.com)\n");
> +	} else {
> +		pr_warn("SWIOTLB overflow buffer is disabled and will be\n"
> +			"  deprecated. Please report problems related to\n"
> +			"  disabling overflow buffer to\n"
> +			"  linux-kernel@...r.kernel.org,\n"
> +			"  Shuah Khan (shuahkhan@...il.com), and\n"
> +			"  Konrad Wilk (konrad.wilk@...cle.com)\n");
> +	}
> +}
> +
>  static int __init
>  setup_io_tlb_npages(char *str)
>  {
> @@ -108,7 +133,6 @@ setup_io_tlb_npages(char *str)
>  	return 1;
>  }
>  __setup("swiotlb=", setup_io_tlb_npages);
> -/* make io_tlb_overflow tunable too? */
>  
>  unsigned long swiotlb_nr_tbl(void)
>  {
> @@ -156,12 +180,18 @@ void __init swiotlb_init_with_tbl(char *tlb, unsigned long nslabs, int verbose)
>  	io_tlb_index = 0;
>  	io_tlb_orig_addr = alloc_bootmem_pages(PAGE_ALIGN(io_tlb_nslabs * sizeof(phys_addr_t)));
>  
> -	/*
> -	 * Get the overflow emergency buffer
> -	 */
> -	io_tlb_overflow_buffer = alloc_bootmem_low_pages(PAGE_ALIGN(io_tlb_overflow));
> -	if (!io_tlb_overflow_buffer)
> -		panic("Cannot allocate SWIOTLB overflow buffer!\n");
> +	if (io_tlb_overflow) {
> +		/*
> +		 * Get the overflow emergency buffer
> +		 */
> +		io_tlb_overflow_buffer = alloc_bootmem_low_pages(
> +						PAGE_ALIGN(io_tlb_overflow));
> +		if (!io_tlb_overflow_buffer)
> +			panic("Cannot allocate SWIOTLB overflow buffer!\n");
> +	}
> +
> +	swiotlb_print_overflow_deprecation_notice();
> +
>  	if (verbose)
>  		swiotlb_print_info();
>  }
> @@ -264,14 +294,17 @@ swiotlb_late_init_with_default_size(size_t default_size)
>  
>  	memset(io_tlb_orig_addr, 0, io_tlb_nslabs * sizeof(phys_addr_t));
>  
> -	/*
> -	 * Get the overflow emergency buffer
> -	 */
> -	io_tlb_overflow_buffer = (void *)__get_free_pages(GFP_DMA,
> -	                                          get_order(io_tlb_overflow));
> -	if (!io_tlb_overflow_buffer)
> -		goto cleanup4;
> +	if (io_tlb_overflow) {
> +		/*
> +		 * Get the overflow emergency buffer
> +		 */
> +		io_tlb_overflow_buffer = (void *)
> +			__get_free_pages(GFP_DMA, get_order(io_tlb_overflow));
> +		if (!io_tlb_overflow_buffer)
> +			goto cleanup4;
> +	}
>  
> +	swiotlb_print_overflow_deprecation_notice();
>  	swiotlb_print_info();
>  
>  	late_alloc = 1;
> @@ -297,12 +330,13 @@ cleanup1:
>  
>  void __init swiotlb_free(void)
>  {
> -	if (!io_tlb_overflow_buffer)
> +	if (!io_tlb_orig_addr)
>  		return;
>  
>  	if (late_alloc) {
> -		free_pages((unsigned long)io_tlb_overflow_buffer,
> -			   get_order(io_tlb_overflow));
> +		if (io_tlb_overflow_buffer)
> +			free_pages((unsigned long)io_tlb_overflow_buffer,
> +				   get_order(io_tlb_overflow));
>  		free_pages((unsigned long)io_tlb_orig_addr,
>  			   get_order(io_tlb_nslabs * sizeof(phys_addr_t)));
>  		free_pages((unsigned long)io_tlb_list, get_order(io_tlb_nslabs *
> @@ -310,8 +344,9 @@ void __init swiotlb_free(void)
>  		free_pages((unsigned long)io_tlb_start,
>  			   get_order(io_tlb_nslabs << IO_TLB_SHIFT));
>  	} else {
> -		free_bootmem_late(__pa(io_tlb_overflow_buffer),
> -				  PAGE_ALIGN(io_tlb_overflow));
> +		if (io_tlb_overflow_buffer)
> +			free_bootmem_late(__pa(io_tlb_overflow_buffer),
> +					  PAGE_ALIGN(io_tlb_overflow));
>  		free_bootmem_late(__pa(io_tlb_orig_addr),
>  				  PAGE_ALIGN(io_tlb_nslabs * sizeof(phys_addr_t)));
>  		free_bootmem_late(__pa(io_tlb_list),
> @@ -681,6 +716,8 @@ dma_addr_t swiotlb_map_page(struct device *dev, struct page *page,
>  	map = map_single(dev, phys, size, dir);
>  	if (!map) {
>  		swiotlb_full(dev, size, dir, 1);
> +		if (!io_tlb_overflow)
> +			return DMA_ERROR_CODE;
>  		map = io_tlb_overflow_buffer;
>  	}
>  
> @@ -691,6 +728,8 @@ dma_addr_t swiotlb_map_page(struct device *dev, struct page *page,
>  	 */
>  	if (!dma_capable(dev, dev_addr, size)) {
>  		swiotlb_tbl_unmap_single(dev, map, size, dir);
> +		if (!io_tlb_overflow)
> +			return DMA_ERROR_CODE;
>  		dev_addr = swiotlb_virt_to_bus(dev, io_tlb_overflow_buffer);
>  	}
>  
> @@ -910,6 +949,8 @@ EXPORT_SYMBOL(swiotlb_sync_sg_for_device);
>  int
>  swiotlb_dma_mapping_error(struct device *hwdev, dma_addr_t dma_addr)
>  {
> +	if (!io_tlb_overflow)
> +		return DMA_ERROR_CODE;
>  	return (dma_addr == swiotlb_virt_to_bus(hwdev, io_tlb_overflow_buffer));
>  }
>  EXPORT_SYMBOL(swiotlb_dma_mapping_error);
> -- 
> 1.7.9.5
> 
> 
> 
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