powerpc/tm: Fix context switching TAR, PPR and DSCR SPRs

If a transaction is rolled back, the Target Address Register (TAR), Processor
Priority Register (PPR) and Data Stream Control Register (DSCR) should be
restored to the checkpointed values before the transaction began.  Any changes
to these SPRs inside the transaction should not be visible in the abort
handler.

Currently Linux doesn't save or restore the checkpointed TAR, PPR or DSCR.  If
we preempt a processes inside a transaction which has modified any of these, on
process restore, that same transaction may be aborted we but we won't see the
checkpointed versions of these SPRs.

This adds checkpointed versions of these SPRs to the thread_struct and adds the
save/restore of these three SPRs to the treclaim/trechkpt code.

Without this if any of these SPRs are modified during a transaction, users may
incorrectly see a speculated SPR value even if the transaction is aborted.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Cc: <stable@vger.kernel.org> [v3.10]
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

3 files changed, 27 insertions, 0 deletions

diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h
index 47a35b08b963..e378cccfca55 100644
--- a/arch/powerpc/include/asm/processor.h
+++ b/arch/powerpc/include/asm/processor.h
@@ -247,6 +247,10 @@ struct thread_struct {
         unsigned long   tm_orig_msr;    /* Thread's MSR on ctx switch */
         struct pt_regs  ckpt_regs;      /* Checkpointed registers */
 
+        unsigned long   tm_tar;
+        unsigned long   tm_ppr;
+        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!
diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
index c7e8afc2ead0..8207459efe56 100644
--- a/arch/powerpc/kernel/asm-offsets.c
+++ b/arch/powerpc/kernel/asm-offsets.c
@@ -138,6 +138,9 @@ int main(void)
         DEFINE(THREAD_TM_TFHAR, offsetof(struct thread_struct, tm_tfhar));
         DEFINE(THREAD_TM_TEXASR, offsetof(struct thread_struct, tm_texasr));
         DEFINE(THREAD_TM_TFIAR, offsetof(struct thread_struct, tm_tfiar));
+        DEFINE(THREAD_TM_TAR, offsetof(struct thread_struct, tm_tar));
+        DEFINE(THREAD_TM_PPR, offsetof(struct thread_struct, tm_ppr));
+        DEFINE(THREAD_TM_DSCR, offsetof(struct thread_struct, tm_dscr));
         DEFINE(PT_CKPT_REGS, offsetof(struct thread_struct, ckpt_regs));
         DEFINE(THREAD_TRANSACT_VR0, offsetof(struct thread_struct,
                                          transact_vr[0]));
diff --git a/arch/powerpc/kernel/tm.S b/arch/powerpc/kernel/tm.S
index 51be8fb24803..0554d1f6d70d 100644
--- a/arch/powerpc/kernel/tm.S
+++ b/arch/powerpc/kernel/tm.S
@@ -233,6 +233,16 @@ dont_backup_fp:
         std     r5, _CCR(r7)
         std     r6, _XER(r7)
 
+
+        /* ******************** TAR, PPR, DSCR ********** */
+        mfspr   r3, SPRN_TAR
+        mfspr   r4, SPRN_PPR
+        mfspr   r5, SPRN_DSCR
+
+        std     r3, THREAD_TM_TAR(r12)
+        std     r4, THREAD_TM_PPR(r12)
+        std     r5, THREAD_TM_DSCR(r12)
+
         /* MSR and flags:  We don't change CRs, and we don't need to alter
          * MSR.
          */
@@ -347,6 +357,16 @@ dont_restore_fp:
         mtmsr   r6                              /* FP/Vec off again! */
 
 restore_gprs:
+
+        /* ******************** TAR, PPR, DSCR ********** */
+        ld      r4, THREAD_TM_TAR(r3)
+        ld      r5, THREAD_TM_PPR(r3)
+        ld      r6, THREAD_TM_DSCR(r3)
+
+        mtspr   SPRN_TAR,       r4
+        mtspr   SPRN_PPR,       r5
+        mtspr   SPRN_DSCR,      r6
+
         /* ******************** CR,LR,CCR,MSR ********** */
         ld      r3, _CTR(r7)
         ld      r4, _LINK(r7)