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Date: Mon, 27 Aug 2012 06:38:16 -0600
From: Shuah Khan <shuah.khan@...com>
To: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc: fujita.tomonori@....ntt.co.jp, akpm@...ux-foundation.org,
paul.gortmaker@...driver.com, bhelgaas@...gle.com,
amwang@...hat.com, LKML <linux-kernel@...r.kernel.org>,
linux-doc@...r.kernel.org, rob@...dley.net, shuahkhan@...il.com
Subject: Re: [PATCH] swiotlb: Add support to disable swiotlb overflow buffer
with deprecation warning
On Sat, 2012-08-25 at 14:25 -0400, Konrad Rzeszutek Wilk wrote:
> On Fri, Aug 24, 2012 at 03:14:05PM -0600, Shuah Khan wrote:
> > Add support for disabling swiotlb overflow buffer using zero size swiotlb
> > overflow buffer to help test disable overflow scenarios to find drivers that
> > don't check dma mapping errors. Add kernel error message to track overflow
> > buffer triggers to understand how often overflow buffer gets used. Add
> > deprecation notice warning message and deprecation schedule documentation, as
> > a first step towards removing overflow support, to be consistent with other
> > iommu implementations and return DMA_ERROR_CODE. Once drivers are fixed
> > overflow support can be removed.
>
> This looks like the previous patch. I thought we discussed this and
> decided that the overflow buffer support should not be disabled outright
> (meaning by default it is ON) - but we can provide a knob to turn it
> off.
No change in plans. This patch doesn't disable the overflow buffer. I
kept the functionality from my earlier patch that checks if overflow
buffer size is 0 and not allocate overflow buffer as a way to disable it
for testing. By default the size is 32*1024 and gets crates as usual and
maintains returning the overflow buffer when swiotlb is full.
>
> And alongside you were going to look at DMA API debug code to see if you
> can come up with a mechanism to track that the users of DMA API call
> dma_mapping_error after they have called various variants of 'map'?
I am working on this now.
-- Shuah
>
> >
> > Tested on x86-64 and compile tested on IA64.
> >
> > Signed-off-by: Shuah Khan <shuah.khan@...com>
> > ---
> > Documentation/feature-removal-schedule.txt | 15 ++++++
> > lib/swiotlb.c | 73 ++++++++++++++++++++--------
> > 2 files changed, 69 insertions(+), 19 deletions(-)
> >
> > diff --git a/Documentation/feature-removal-schedule.txt b/Documentation/feature-removal-schedule.txt
> > index a52924e..b5938ca 100644
> > --- a/Documentation/feature-removal-schedule.txt
> > +++ b/Documentation/feature-removal-schedule.txt
> > @@ -646,3 +646,18 @@ Who: Russell King <linux@....linux.org.uk>,
> > Santosh Shilimkar <santosh.shilimkar@...com>
> >
> > ----------------------------
> > +
> > +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 3.7, add logging to track swiotlb
> > + buffer overflow triggers to understand how often overflow buffer
> > + gets used. The next step is to fix drivers that don't call
> > + dma_mapping_error to check for errors returned by the mapping
> > + interfaces. 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..658f35a 100644
> > --- a/lib/swiotlb.c
> > +++ b/lib/swiotlb.c
> > @@ -92,6 +92,24 @@ 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 +126,6 @@ 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 +173,18 @@ 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 +287,17 @@ 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 +323,13 @@ 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 +337,9 @@ 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),
> > @@ -681,7 +709,10 @@ 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;
> > + dev_err(dev, "SWIOTLB is full. Mapping overflow buffer.\n");
> > }
> >
> > dev_addr = swiotlb_virt_to_bus(dev, map);
> > @@ -691,6 +722,8 @@ 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 +943,8 @@ 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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