• Tomasz Nowicki's avatar
    iommu/iova: Make rcache flush optional on IOVA allocation failure · 538d5b33
    Tomasz Nowicki authored
    Since IOVA allocation failure is not unusual case we need to flush
    CPUs' rcache in hope we will succeed in next round.
    
    However, it is useful to decide whether we need rcache flush step because
    of two reasons:
    - Not scalability. On large system with ~100 CPUs iterating and flushing
      rcache for each CPU becomes serious bottleneck so we may want to defer it.
    - free_cpu_cached_iovas() does not care about max PFN we are interested in.
      Thus we may flush our rcaches and still get no new IOVA like in the
      commonly used scenario:
    
        if (dma_limit > DMA_BIT_MASK(32) && dev_is_pci(dev))
            iova = alloc_iova_fast(iovad, iova_len, DMA_BIT_MASK(32) >> shift);
    
        if (!iova)
            iova = alloc_iova_fast(iovad, iova_len, dma_limit >> shift);
    
       1. First alloc_iova_fast() call is limited to DMA_BIT_MASK(32) to get
          PCI devices a SAC address
       2. alloc_iova() fails due to full 32-bit space
       3. rcaches contain PFNs out of 32-bit space so free_cpu_cached_iovas()
          throws entries away for nothing and alloc_iova() fails again
       4. Next alloc_iova_fast() call cannot take advantage of rcache since we
          have just defeated caches. In this case we pick the slowest option
          to proceed.
    
    This patch reworks flushed_rcache local flag to be additional function
    argument instead and control rcache flush step. Also, it updates all users
    to do the flush as the last chance.
    Signed-off-by: default avatarTomasz Nowicki <Tomasz.Nowicki@caviumnetworks.com>
    Reviewed-by: default avatarRobin Murphy <robin.murphy@arm.com>
    Tested-by: default avatarNate Watterson <nwatters@codeaurora.org>
    Signed-off-by: default avatarJoerg Roedel <jroedel@suse.de>
    538d5b33
dma-iommu.c 25.6 KB