On Thu, 2015-06-11 at 16:25 +0200, Joerg Roedel wrote: > On Thu, Jun 11, 2015 at 03:07:02PM +0100, David Woodhouse wrote: > > On Thu, 2015-06-11 at 15:47 +0200, Joerg Roedel wrote: > > > From: Joerg Roedel <[email protected]> > > > > > > Hide the copied context entries from the IOMMU driver by > > > considering them as non-present. This is implemented by > > > setting the first AVL bit (bit 67) in the context entry to > > > one. If this bit is set, the context_present() function > > > returns false. > > > > > > Signed-off-by: Joerg Roedel <[email protected]> > > > > In the extended context entry, bit 67 is the PGE bit. There are no bits > > which are available to software, to my knowledge. > > Okay, reading the VT-d spec again, the extended context-entry table seem > to exist in parallel to the current context-entry table, right? So this > patch should still work, even with extended entries present.
No, the extended context-entry exists *instead* of the legacy
context-entry. Note that all the bits in the legacy context-entry are
present in precisely the same place in the extended context-entry. It's
just that the extended context-entry defines meanings for more of them.
When you enable the DMA_RTADDR_RTT bit in the Root Table Address
register, the context-entries magically double in size.
It used to look like this:
Root Table Address Register
|
V
Root Table (struct root_entry) Context Table (struct context_entry)
------------------------------ ------------------------------------
0x00: Context-table pointer -----> Context entry for 00:00.0
0x08: unused Context entry for 00:00.1
0x10: unused Context entry for 00:00.2
... ... ...
0xff8:... Context entry for ff:1f.7
Now it looks like this
Root Table Address Register
|
V
Root Table (struct root_entry) Context Table (struct context_entry)
------------------------------ ------------------------------------
0x00: Context-table ptr #1 -----> Context entry for 00:00.0: lo
0x08: Context-table ptr #2 --, Context entry for 00:00.0: hi
0x10: unused | Context entry for 00:00.1: lo
... ... | ...
0xff8:... | Context entry for 7f:1f.7: hi
|
|
| Context Table (struct context_entry)
--> ------------------------------------
0x00: Context entry for 80:00.0: lo
0x08: Context entry for 80:00.1: hi
... ...
0xff8: Context entry for ff:1f.7: hi
This was implemented in http://git.kernel.org/linus/03ecc32c52 but
*all* that patch did was allocate the second page of context-table,
fill in the appropriate new pointer in the root table, and adjust the
way we calculate the *location* of a context-entry. In 4.1 we're still
only using the same old bits of the context-entry, which as noted are
in the same place in both cases. Even the mapping from the old 2-bit T
field to the new 3-bit TT field works out that way, for now.
--
dwmw2
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