illumos gate

http://bugs.opensolaris.org/bugdatabase/view_bug.do?bug_id=7001754
Related Bugs 6896869 , 6212057

The KVA mapping created by ddi_dma_mem_alloc() always gets WB/cached cached
attributes even when UC/uncached (DDI_STRICTORDER_ACC) or WC/writecombine
(DDI_MERGING_OK_ACC) are requested. On b151a, the KVA for a single page DMA
buffer that should be UC (KVA 0xffffff01d8828000 PA 0x110412000):

110412::report_maps

hat=ffffff01c707ee78 maps addr=ffffff01d8828000

ffffff01d8828000::vatopfn

level=0 htable=ffffff01d2f288a0 pte=110412363
level=1 htable=ffffff01c7377df0 pte=11b9fc027
level=2 htable=ffffff01c7377d60 pte=b85fb027
level=3 htable=ffffff01c7378ed0 pte=b85ff027
Virtual address 0xffffff01d8828000 maps pfn 0x110412

110412363::pte

pte=110412363: pfn=0x110412 nosync global write

ffffff01d8828000::vatopfn

level=0 htable=ffffff01d2f288a0 pte=110412363
level=1 htable=ffffff01c7377df0 pte=11b9fc027
level=2 htable=ffffff01c7377d60 pte=b85fb027
level=3 htable=ffffff01c7378ed0 pte=b85ff027
Virtual address 0xffffff01d8828000 maps pfn 0x110412

The PTE should say "uncached" (PT_NOCACHE not set). Note this is with
gfx_private::gfxp_fix_mem_cache_attrs() now a NOP.

Here's a single page DMA buffer (KVA 0xffffff01d8828000 PA 0x110412000)
with gfx_private::gfxp_fix_mem_cache_attrs() restored:

13bd36::report_maps

hat=ffffff01c707ee78 maps addr=ffffff01d8a8c000

ffffff01d8a8c000::vatopfn

level=0 htable=ffffff01d395d158 pte=13bd36373
level=1 htable=ffffff01c7377df0 pte=11c14c027
level=2 htable=ffffff01c7377d60 pte=b85fb027
level=3 htable=ffffff01c7378ed0 pte=b85ff027
Virtual address 0xffffff01d8a8c000 maps pfn 0x13bd36

13bd36373::pte

pte=13bd36373: pfn=0x13bd36 nosync global write uncached

ffffff01d8a8c000::vatopfn

level=0 htable=ffffff01d395d158 pte=13bd36373
level=1 htable=ffffff01c7377df0 pte=11c14c027
level=2 htable=ffffff01c7377d60 pte=b85fb027
level=3 htable=ffffff01c7378ed0 pte=b85ff027
Virtual address 0xffffff01d8a8c000 maps pfn 0x13bd36

Note the PTE has "uncached" (PT_NOCACHE set).