minor fix for tlb manipulations

Andrew Duane aduane at juniper.net
Mon Apr 28 12:55:37 UTC 2008

Our version of the MIPS code does in fact use the number of pairs, not number of entries, so we are not affected by this issue. I'm not sure how the "virgin" FreeBSD code works, though, we've modified this section somewhat.

-----Original Message-----
From: owner-freebsd-mips at freebsd.org on behalf of M. Warner Losh
Sent: Sun 4/27/2008 1:21 AM
To: nao at tom-yam.or.jp
Cc: freebsd-mips at freebsd.org
Subject: Re: minor fix for tlb manipulations
In message: <2da2ec620804222103r7e90af37j2d36b0f0bc049abb at mail.gmail.com>
            "Naoki Hamada" <nao at tom-yam.or.jp> writes:
: I found a slight problem in tlb.S which tries to manipulate
: no-existing tlbs. The argument of Mips_TLBFlush() and mips_TBIAP() is
: the number of tlbs to deal with, but both functions process the same
: number of tlb pairs, so twice the number of actual tlbs.

I believe that the argument is the number of pairs to invalidate, at
least in the case of Mips_TLBFlush.  The number passed in is the
MMUSize field from CO_Config1, which indicates the number of pairs
that exist in the tlb.  True, each iteration of the loop invalidates a
pair of TLB entires, I think that the code is correct as it is.  The
MMUSize field returns the number of pairs, so I don't think any
biasing is needed.

The current Mips_TLBFlush function matches the InitTLB function given
in the MIPS32 Architecture for Programmers, Volume III.

: TLBWI entry of "MIPS32 Architecture For Programmers Volume II: The
: MIPS32 Instruction Set" states that "The operation is UNDEFINED if the
: contents of the Index register are greater than or equal to the number
: of TLB entries in the processor." It seems to do no harm to my system,
: but your mileage may vary.

Correct.  However, the count is the number of pairs, not the total

Have I missed something in my reading the code and the mips32 specs?

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