powerpc: tm: Always use fp_state and vr_state to store live registers

There is currently an inconsistency as to how the entire CPU register
state is saved and restored when a thread uses transactional memory
(TM).

Using transactional memory results in the CPU having duplicated
(almost) all of its register state. This duplication results in a set
of registers which can be considered 'live', those being currently
modified by the instructions being executed and another set that is
frozen at a point in time.

On context switch, both sets of state have to be saved and (later)
restored. These two states are often called a variety of different
things. Common terms for the state which only exists after the CPU has
entered a transaction (performed a TBEGIN instruction) in hardware are
'transactional' or 'speculative'.

Between a TBEGIN and a TEND or TABORT (or an event that causes the
hardware to abort), regardless of the use of TSUSPEND the
transactional state can be referred to as the live state.

The second state is often to referred to as the 'checkpointed' state
and is a duplication of the live state when the TBEGIN instruction is
executed. This state is kept in the hardware and will be rolled back
to on transaction failure.

Currently all the registers stored in pt_regs are ALWAYS the live
registers, that is, when a thread has transactional registers their
values are stored in pt_regs and the checkpointed state is in
ckpt_regs. A strange opposite is true for fp_state/vr_state. When a
thread is non transactional fp_state/vr_state holds the live
registers. When a thread has initiated a transaction fp_state/vr_state
holds the checkpointed state and transact_fp/transact_vr become the
structure which holds the live state (at this point it is a
transactional state).

This method creates confusion as to where the live state is, in some
circumstances it requires extra work to determine where to put the
live state and prevents the use of common functions designed (probably
before TM) to save the live state.

With this patch pt_regs, fp_state and vr_state all represent the
same thing and the other structures [pending rename] are for
checkpointed state.

Acked-by: Simon Guo <wei.guo.simon@gmail.com>
Signed-off-by: Cyril Bur <cyrilbur@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 2 insertions, 5 deletions

diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h
index 68e3bf57b027..feab2ce72940 100644
--- a/arch/powerpc/include/asm/processor.h
+++ b/arch/powerpc/include/asm/processor.h
@@ -267,16 +267,13 @@ struct thread_struct {
 	unsigned long	tm_dscr;
 
 	/*
-	 * Transactional FP and VSX 0-31 register set.
-	 * NOTE: the sense of these is the opposite of the integer ckpt_regs!
+	 * Checkpointed FP and VSX 0-31 register set.
 	 *
 	 * When a transaction is active/signalled/scheduled etc., *regs is the
 	 * most recent set of/speculated GPRs with ckpt_regs being the older
 	 * checkpointed regs to which we roll back if transaction aborts.
 	 *
-	 * However, fpr[] is the checkpointed 'base state' of FP regs, and
-	 * transact_fpr[] is the new set of transactional values.
-	 * VRs work the same way.
+	 * These are analogous to how ckpt_regs and pt_regs work
 	 */
 	struct thread_fp_state transact_fp;
 	struct thread_vr_state transact_vr;