iommu/vt-d: Fix incorrect iommu_count for si_domain

iommu/vt-d: Fix incorrect iommu_count for si_domain

The iommu_count field in si_domain(static identity domain) is
initialized to zero and never increases. It will underflow
when tearing down iommu unit in function free_dmar_iommu()
and leak memory. So refine code to correctly manage
si_domain->iommu_count.

Warning message caused by si_domain memory leak:
[   14.609681] IOMMU: Setting RMRR:
[   14.613496] Ignoring identity map for HW passthrough device 0000:00:1a.0 [0xbdcfd000 - 0xbdd1dfff]
[   14.623809] Ignoring identity map for HW passthrough device 0000:00:1d.0 [0xbdcfd000 - 0xbdd1dfff]
[   14.634162] IOMMU: Prepare 0-16MiB unity mapping for LPC
[   14.640329] Ignoring identity map for HW passthrough device 0000:00:1f.0 [0x0 - 0xffffff]
[   14.673360] IOMMU: dmar init failed
[   14.678157] kmem_cache_destroy iommu_devinfo: Slab cache still has objects
[   14.686076] CPU: 12 PID: 1 Comm: swapper/0 Not tainted 3.13.0-rc1-gerry+ #59
[   14.694176] Hardware name: Intel Corporation LH Pass ........../SVRBD-ROW_T, BIOS SE5C600.86B.99.99.x059.091020121352 09/10/2012
[   14.707412]  0000000000000000 ffff88042dd33db0 ffffffff8156223d ffff880c2cc37c00
[   14.716407]  ffff88042dd33dc8 ffffffff811790b1 ffff880c2d3533b8 ffff88042dd33e00
[   14.725468]  ffffffff81dc7a6a ffffffff81b1e8e0 ffffffff81f84058 ffffffff81d8a711
[   14.734464] Call Trace:
[   14.737453]  [<ffffffff8156223d>] dump_stack+0x4d/0x66
[   14.743430]  [<ffffffff811790b1>] kmem_cache_destroy+0xf1/0x100
[   14.750279]  [<ffffffff81dc7a6a>] intel_iommu_init+0x122/0x56a
[   14.757035]  [<ffffffff81d8a711>] ? iommu_setup+0x27d/0x27d
[   14.763491]  [<ffffffff81d8a739>] pci_iommu_init+0x28/0x52
[   14.769846]  [<ffffffff81000342>] do_one_initcall+0x122/0x180
[   14.776506]  [<ffffffff81077738>] ? parse_args+0x1e8/0x320
[   14.782866]  [<ffffffff81d850e8>] kernel_init_freeable+0x1e1/0x26c
[   14.789994]  [<ffffffff81d84833>] ? do_early_param+0x88/0x88
[   14.796556]  [<ffffffff8154ffc0>] ? rest_init+0xd0/0xd0
[   14.802626]  [<ffffffff8154ffce>] kernel_init+0xe/0x130
[   14.808698]  [<ffffffff815756ac>] ret_from_fork+0x7c/0xb0
[   14.814963]  [<ffffffff8154ffc0>] ? rest_init+0xd0/0xd0
[   14.821640] kmem_cache_destroy iommu_domain: Slab cache still has objects
[   14.829456] CPU: 12 PID: 1 Comm: swapper/0 Not tainted 3.13.0-rc1-gerry+ #59
[   14.837562] Hardware name: Intel Corporation LH Pass ........../SVRBD-ROW_T, BIOS SE5C600.86B.99.99.x059.091020121352 09/10/2012
[   14.850803]  0000000000000000 ffff88042dd33db0 ffffffff8156223d ffff88102c1ee3c0
[   14.861222]  ffff88042dd33dc8 ffffffff811790b1 ffff880c2d3533b8 ffff88042dd33e00
[   14.870284]  ffffffff81dc7a76 ffffffff81b1e8e0 ffffffff81f84058 ffffffff81d8a711
[   14.879271] Call Trace:
[   14.882227]  [<ffffffff8156223d>] dump_stack+0x4d/0x66
[   14.888197]  [<ffffffff811790b1>] kmem_cache_destroy+0xf1/0x100
[   14.895034]  [<ffffffff81dc7a76>] intel_iommu_init+0x12e/0x56a
[   14.901781]  [<ffffffff81d8a711>] ? iommu_setup+0x27d/0x27d
[   14.908238]  [<ffffffff81d8a739>] pci_iommu_init+0x28/0x52
[   14.914594]  [<ffffffff81000342>] do_one_initcall+0x122/0x180
[   14.921244]  [<ffffffff81077738>] ? parse_args+0x1e8/0x320
[   14.927598]  [<ffffffff81d850e8>] kernel_init_freeable+0x1e1/0x26c
[   14.934738]  [<ffffffff81d84833>] ? do_early_param+0x88/0x88
[   14.941309]  [<ffffffff8154ffc0>] ? rest_init+0xd0/0xd0
[   14.947380]  [<ffffffff8154ffce>] kernel_init+0xe/0x130
[   14.953430]  [<ffffffff815756ac>] ret_from_fork+0x7c/0xb0
[   14.959689]  [<ffffffff8154ffc0>] ? rest_init+0xd0/0xd0
[   14.966299] kmem_cache_destroy iommu_iova: Slab cache still has objects
[   14.973923] CPU: 12 PID: 1 Comm: swapper/0 Not tainted 3.13.0-rc1-gerry+ #59
[   14.982020] Hardware name: Intel Corporation LH Pass ........../SVRBD-ROW_T, BIOS SE5C600.86B.99.99.x059.091020121352 09/10/2012
[   14.995263]  0000000000000000 ffff88042dd33db0 ffffffff8156223d ffff88042cb5c980
[   15.004265]  ffff88042dd33dc8 ffffffff811790b1 ffff880c2d3533b8 ffff88042dd33e00
[   15.013322]  ffffffff81dc7a82 ffffffff81b1e8e0 ffffffff81f84058 ffffffff81d8a711
[   15.022318] Call Trace:
[   15.025238]  [<ffffffff8156223d>] dump_stack+0x4d/0x66
[   15.031202]  [<ffffffff811790b1>] kmem_cache_destroy+0xf1/0x100
[   15.038038]  [<ffffffff81dc7a82>] intel_iommu_init+0x13a/0x56a
[   15.044786]  [<ffffffff81d8a711>] ? iommu_setup+0x27d/0x27d
[   15.051242]  [<ffffffff81d8a739>] pci_iommu_init+0x28/0x52
[   15.057601]  [<ffffffff81000342>] do_one_initcall+0x122/0x180
[   15.064254]  [<ffffffff81077738>] ? parse_args+0x1e8/0x320
[   15.070608]  [<ffffffff81d850e8>] kernel_init_freeable+0x1e1/0x26c
[   15.077747]  [<ffffffff81d84833>] ? do_early_param+0x88/0x88
[   15.084300]  [<ffffffff8154ffc0>] ? rest_init+0xd0/0xd0
[   15.090362]  [<ffffffff8154ffce>] kernel_init+0xe/0x130
[   15.096431]  [<ffffffff815756ac>] ret_from_fork+0x7c/0xb0
[   15.102693]  [<ffffffff8154ffc0>] ? rest_init+0xd0/0xd0
[   15.189273] PCI-DMA: Using software bounce buffering for IO (SWIOTLB)

Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
Cc: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Joerg Roedel <joro@8bytes.org>