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Update documentation in smmrelocate.S to mention TSEG

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Change-Id: I392f5fc475b15b458fc015e176e45888e7de27fb
Signed-off-by: Stefan Reinauer <reinauer@google.com>
Reviewed-on: http://review.coreboot.org/861
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
This commit is contained in:
Stefan Reinauer
2012-04-04 10:38:05 -07:00
parent 5c55463f50
commit 8c5b58e7c3
1 changed files with 11 additions and 8 deletions
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19
src/cpu/x86/smm/smmrelocate.S
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@@ -54,13 +54,22 @@
.code16
/**
* This trampoline code relocates SMBASE to 0xa0000 - ( lapicid * 0x400 )
* When starting up, x86 CPUs have their SMBASE set to 0x30000. However,
* this is not a good place for the SMM handler to live, so it needs to
* be relocated.
* Traditionally SMM handlers used to live in the A segment (0xa0000).
* With growing SMM handlers, more CPU cores, etc. CPU vendors started
* allowing to relocate the handler to the end of physical memory, which
* they refer to as TSEG.
* This trampoline code relocates SMBASE to base address - ( lapicid * 0x400 )
*
* Why 0x400? It is a safe value to cover the save state area per CPU. On
* current AMD CPUs this area is _documented_ to be 0x200 bytes. On Intel
* Core 2 CPUs the _documented_ parts of the save state area is 48 bytes
* bigger, effectively sizing our data structures 0x300 bytes.
*
* Example (with SMM handler living at 0xa0000):
*
* LAPICID SMBASE SMM Entry SAVE STATE
* 0 0xa0000 0xa8000 0xafd00
* 1 0x9fc00 0xa7c00 0xaf900
@@ -88,13 +97,7 @@
* at 0xa8000-0xa8100 (example for core 0). That is not enough.
*
* This means we're basically limited to 16 cpu cores before
* we need to use the TSEG/HSEG for the actual SMM handler plus stack.
* When we exceed 32 cores, we also need to put SMBASE to TSEG/HSEG.
*
* If we figure out the documented values above are safe to use,
* we could pack the structure above even more, so we could use the
* scheme to pack save state areas for 63 AMD CPUs or 58 Intel CPUs
* in the ASEG.
* we need to move the SMM handler to TSEG.
*
* Note: Some versions of Pentium M need their SMBASE aligned to 32k.
* On those the above only works for up to 2 cores. But for now we only