On Mar 23, 2007, at 9:07 AM, Hollis Blanchard wrote:
On Fri, 2007-03-23 at 08:52 +0100, Christian Ehrhardt wrote:
Jimi Xenidis wrote:
...
Ensure MMCR0[FCH] for this first step:
-(ensure) set MMCR[FCH] always in xen when entering xen space. This
should prevent a domain
messing up MMCR0[FCH]
->EXCEPTION_HEAD in exception.S set MMCR0[FCH] always
You need at least the following instructions:
mfspr r0, SPRN_MMCR0
ori r0, r0, 1 /* MMRC0_FCH */
mtspr 795, SPRN_MMCR0
Unfortuantely, there is not enough room in EXCEPTION_HEAD for
that and
you will get:
exceptions.S: Assembler messages:
exceptions.S:246: Error: attempt to .org/.space backwards? (-4)
exceptions.S:253: Error: attempt to .org/.space backwards? (-4)
exceptions.S:260: Error: attempt to .org/.space backwards? (-4)
exceptions.S:267: Error: attempt to .org/.space backwards? (-4)
exceptions.o: Bad value
exceptions.S:626: FATAL: Can't write exceptions.o: Bad value
I suggest we start a new macro PMU_SAVE_STATE(save,scratch), which
does the above (for now, using only scratch) and sprinkling it in
all
the code that EXCEPTION_HEAD branches to.
Yep, I had those already:
mfspr r0,SPRN_MMCR0 /* ensure MMCR0[FCH]=1 */
ori r0,r0,MMCR0_FCH
mtspr SPRN_MMCR0, r0
Do you mean to insert a branch to PMU_SAVE_STATE from
EXCEPTION_HEAD or
to put a PMU_SAVE_STATE branch to every section calling
EXCEPTION_HEAD ?
Can someone please point at a code piece that does a similar macro
definition and branch already.
We have 0x80 bytes for the "top half" of our exception handlers.
This is
dictated by hardware: there are vectors at 0x300 and 0x380, so our
code
must fit in that much space. If you do the math, that means we have
room
for 32 instructions, including a branch to the rest of the handler
(named "ex_*_continued"). Right now, we use 30 instructions. So
without
doing major exception handler surgery, your three new instructions
will
need to go after the branch.
Side note: I think it's ridiculous that our architecture allows the
guest to set MMCR0:FCH, since that bit controls the CPU while in
hypervisor mode. Anyways, disabling that bit a few dozen instructions
later shouldn't make a difference, and the domain never should have
set
it in the first place.
Alternatively we could setup an "assist" session with screen -x
developing this part together if there is a volunteer.
I created this one blindly now as a start
.macro PMU_SAVE_STATE save scratch
mfspr \scratch,SPRN_MMCR0 /* ensure MMCR0[FCH]
=1,
not yet saving anything */
ori \scratch,\scratch,MMCR0_FCH
mtspr SPRN_MMCR0, \scratch
.endm
and added the following to EXCEPTION_HEAD, but I guess it it wrong
that
way ;)
PMU_SAVE_STATE r0 r0
Right, that won't fit in EXCEPTION_HEAD (you will get the assembler
error messages Jimi pasted above).
Yeah,
So EXCEPTION_HEAD branches to a passed in label. Find all those
labels and insert PMU_SAVE_STATE there.
-JX
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