powerpc/tm: Save and restore AMR on treclaim and trechkpt

Althought AMR is stashed in the checkpoint area, currently we don't save
it to the per thread checkpoint struct after a treclaim and so we don't
restore it either from that struct when we trechkpt. As a consequence when
the transaction is later rolled back the kernel space AMR value when the
trechkpt was done appears in userspace.

That commit saves and restores AMR accordingly on treclaim and trechkpt.
Since AMR value is also used in kernel space in other functions, it also
takes care of stashing kernel live AMR into the stack before treclaim and
before trechkpt, restoring it later, just before returning from tm_reclaim
and __tm_recheckpoint.

Is also fixes two nonrelated comments about CR and MSR.
Signed-off-by: Gustavo Romero <gromero@linux.ibm.com>
Tested-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200919150025.9609-1-gromero@linux.ibm.com

arch/powerpc/include/asm/processor.h

@@ -220,6 +220,7 @@ struct thread_struct {
 	unsigned long	tm_tar;
 	unsigned long	tm_ppr;
 	unsigned long	tm_dscr;
+	unsigned long   tm_amr;
 
 	/*
 	 * Checkpointed FP and VSX 0-31 register set.

arch/powerpc/kernel/asm-offsets.c

@@ -176,6 +176,7 @@ int main(void)
 	OFFSET(THREAD_TM_TAR, thread_struct, tm_tar);
 	OFFSET(THREAD_TM_PPR, thread_struct, tm_ppr);
 	OFFSET(THREAD_TM_DSCR, thread_struct, tm_dscr);
+	OFFSET(THREAD_TM_AMR, thread_struct, tm_amr);
 	OFFSET(PT_CKPT_REGS, thread_struct, ckpt_regs);
 	OFFSET(THREAD_CKVRSTATE, thread_struct, ckvr_state.vr);
 	OFFSET(THREAD_CKVRSAVE, thread_struct, ckvrsave);

arch/powerpc/kernel/tm.S

@@ -122,6 +122,13 @@ _GLOBAL(tm_reclaim)
 	std	r3, STK_PARAM(R3)(r1)
 	SAVE_NVGPRS(r1)
 
+	/*
+	 * Save kernel live AMR since it will be clobbered by treclaim
+	 * but can be used elsewhere later in kernel space.
+	 */
+	mfspr	r3, SPRN_AMR
+	std	r3, TM_FRAME_L1(r1)
+
 	/* We need to setup MSR for VSX register save instructions. */
 	mfmsr	r14
 	mr	r15, r14
@@ -245,7 +252,7 @@ _GLOBAL(tm_reclaim)
 	 * but is used in signal return to 'wind back' to the abort handler.
 	 */
 
-	/* ******************** CR,LR,CCR,MSR ********** */
+	/* ***************** CTR, LR, CR, XER ********** */
 	mfctr	r3
 	mflr	r4
 	mfcr	r5
@@ -256,7 +263,6 @@ _GLOBAL(tm_reclaim)
 	std	r5, _CCR(r7)
 	std	r6, _XER(r7)
 
-
 	/* ******************** TAR, DSCR ********** */
 	mfspr	r3, SPRN_TAR
 	mfspr	r4, SPRN_DSCR
@@ -264,6 +270,10 @@ _GLOBAL(tm_reclaim)
 	std	r3, THREAD_TM_TAR(r12)
 	std	r4, THREAD_TM_DSCR(r12)
 
+        /* ******************** AMR **************** */
+        mfspr	r3, SPRN_AMR
+        std	r3, THREAD_TM_AMR(r12)
+
 	/*
 	 * MSR and flags: We don't change CRs, and we don't need to alter MSR.
 	 */
@@ -308,7 +318,9 @@ _GLOBAL(tm_reclaim)
 	std	r3, THREAD_TM_TFHAR(r12)
 	std	r4, THREAD_TM_TFIAR(r12)
 
-	/* AMR is checkpointed too, but is unsupported by Linux. */
+	/* Restore kernel live AMR */
+	ld	r8, TM_FRAME_L1(r1)
+	mtspr	SPRN_AMR, r8
 
 	/* Restore original MSR/IRQ state & clear TM mode */
 	ld	r14, TM_FRAME_L0(r1)		/* Orig MSR */
@@ -355,6 +367,13 @@ _GLOBAL(__tm_recheckpoint)
 	 */
 	SAVE_NVGPRS(r1)
 
+	/*
+	 * Save kernel live AMR since it will be clobbered for trechkpt
+	 * but can be used elsewhere later in kernel space.
+	 */
+	mfspr	r8, SPRN_AMR
+	std	r8, TM_FRAME_L0(r1)
+
 	/* Load complete register state from ts_ckpt* registers */
 
 	addi	r7, r3, PT_CKPT_REGS		/* Thread's ckpt_regs */
@@ -404,7 +423,7 @@ _GLOBAL(__tm_recheckpoint)
 
 restore_gprs:
 
-	/* ******************** CR,LR,CCR,MSR ********** */
+	/* ****************** CTR, LR, XER ************* */
 	ld	r4, _CTR(r7)
 	ld	r5, _LINK(r7)
 	ld	r8, _XER(r7)
@@ -417,6 +436,10 @@ restore_gprs:
 	ld	r4, THREAD_TM_TAR(r3)
 	mtspr	SPRN_TAR,	r4
 
+	/* ******************** AMR ******************** */
+	ld	r4, THREAD_TM_AMR(r3)
+	mtspr	SPRN_AMR, r4
+
 	/* Load up the PPR and DSCR in GPRs only at this stage */
 	ld	r5, THREAD_TM_DSCR(r3)
 	ld	r6, THREAD_TM_PPR(r3)
@@ -509,6 +532,10 @@ restore_gprs:
 	li	r4, MSR_RI
 	mtmsrd	r4, 1
 
+	/* Restore kernel live AMR */
+	ld	r8, TM_FRAME_L0(r1)
+	mtspr	SPRN_AMR, r8
+
 	REST_NVGPRS(r1)
 
 	addi    r1, r1, TM_FRAME_SIZE