powerpc/64s: avoid reloading (H)SRR registers if they are still valid

When an interrupt is taken, the SRR registers are set to return to where
it left off. Unless they are modified in the meantime, or the return
address or MSR are modified, there is no need to reload these registers
when returning from interrupt.

Introduce per-CPU flags that track the validity of SRR and HSRR
registers. These are cleared when returning from interrupt, when
using the registers for something else (e.g., OPAL calls), when
adjusting the return address or MSR of a context, and when context
switching (which changes the return address and MSR).

This improves the performance of interrupt returns.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Fold in fixup patch from Nick]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210617155116.2167984-5-npiggin@gmail.com

1 files changed, 23 insertions, 19 deletions

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 4e593fc2c66db..8ab1bfdfd31a2 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -96,7 +96,8 @@ static void check_if_tm_restore_required(struct task_struct *tsk)
 	if (tsk == current && tsk->thread.regs &&
 	    MSR_TM_ACTIVE(tsk->thread.regs->msr) &&
 	    !test_thread_flag(TIF_RESTORE_TM)) {
-		tsk->thread.ckpt_regs.msr = tsk->thread.regs->msr;
+		regs_set_return_msr(&tsk->thread.ckpt_regs,
+						tsk->thread.regs->msr);
 		set_thread_flag(TIF_RESTORE_TM);
 	}
 }
@@ -161,7 +162,7 @@ static void __giveup_fpu(struct task_struct *tsk)
 	msr &= ~(MSR_FP|MSR_FE0|MSR_FE1);
 	if (cpu_has_feature(CPU_FTR_VSX))
 		msr &= ~MSR_VSX;
-	tsk->thread.regs->msr = msr;
+	regs_set_return_msr(tsk->thread.regs, msr);
 }
 
 void giveup_fpu(struct task_struct *tsk)
@@ -244,7 +245,7 @@ static void __giveup_altivec(struct task_struct *tsk)
 	msr &= ~MSR_VEC;
 	if (cpu_has_feature(CPU_FTR_VSX))
 		msr &= ~MSR_VSX;
-	tsk->thread.regs->msr = msr;
+	regs_set_return_msr(tsk->thread.regs, msr);
 }
 
 void giveup_altivec(struct task_struct *tsk)
@@ -559,7 +560,7 @@ void notrace restore_math(struct pt_regs *regs)
 
 		msr_check_and_clear(new_msr);
 
-		regs->msr |= new_msr | fpexc_mode;
+		regs_set_return_msr(regs, regs->msr | new_msr | fpexc_mode);
 	}
 }
 #endif /* CONFIG_PPC_BOOK3S_64 */
@@ -1114,7 +1115,7 @@ void restore_tm_state(struct pt_regs *regs)
 #endif
 	restore_math(regs);
 
-	regs->msr |= msr_diff;
+	regs_set_return_msr(regs, regs->msr | msr_diff);
 }
 
 #else /* !CONFIG_PPC_TRANSACTIONAL_MEM */
@@ -1257,14 +1258,16 @@ struct task_struct *__switch_to(struct task_struct *prev,
 	}
 
 	/*
-	 * Call restore_sprs() before calling _switch(). If we move it after
-	 * _switch() then we miss out on calling it for new tasks. The reason
-	 * for this is we manually create a stack frame for new tasks that
-	 * directly returns through ret_from_fork() or
+	 * Call restore_sprs() and set_return_regs_changed() before calling
+	 * _switch(). If we move it after _switch() then we miss out on calling
+	 * it for new tasks. The reason for this is we manually create a stack
+	 * frame for new tasks that directly returns through ret_from_fork() or
 	 * ret_from_kernel_thread(). See copy_thread() for details.
 	 */
 	restore_sprs(old_thread, new_thread);
 
+	set_return_regs_changed(); /* _switch changes stack (and regs) */
+
 #ifdef CONFIG_PPC32
 	kuap_assert_locked();
 #endif
@@ -1850,13 +1853,14 @@ void start_thread(struct pt_regs *regs, unsigned long start, unsigned long sp)
 			}
 			regs->gpr[2] = toc;
 		}
-		regs->nip = entry;
-		regs->msr = MSR_USER64;
+		regs_set_return_ip(regs, entry);
+		regs_set_return_msr(regs, MSR_USER64);
 	} else {
-		regs->nip = start;
 		regs->gpr[2] = 0;
-		regs->msr = MSR_USER32;
+		regs_set_return_ip(regs, start);
+		regs_set_return_msr(regs, MSR_USER32);
 	}
+
 #endif
 #ifdef CONFIG_VSX
 	current->thread.used_vsr = 0;
@@ -1887,7 +1891,6 @@ void start_thread(struct pt_regs *regs, unsigned long start, unsigned long sp)
 	current->thread.tm_tfiar = 0;
 	current->thread.load_tm = 0;
 #endif /* CONFIG_PPC_TRANSACTIONAL_MEM */
-
 }
 EXPORT_SYMBOL(start_thread);
 
@@ -1935,9 +1938,10 @@ int set_fpexc_mode(struct task_struct *tsk, unsigned int val)
 	if (val > PR_FP_EXC_PRECISE)
 		return -EINVAL;
 	tsk->thread.fpexc_mode = __pack_fe01(val);
-	if (regs != NULL && (regs->msr & MSR_FP) != 0)
-		regs->msr = (regs->msr & ~(MSR_FE0|MSR_FE1))
-			| tsk->thread.fpexc_mode;
+	if (regs != NULL && (regs->msr & MSR_FP) != 0) {
+		regs_set_return_msr(regs, (regs->msr & ~(MSR_FE0|MSR_FE1))
+						| tsk->thread.fpexc_mode);
+	}
 	return 0;
 }
 
@@ -1983,9 +1987,9 @@ int set_endian(struct task_struct *tsk, unsigned int val)
 		return -EINVAL;
 
 	if (val == PR_ENDIAN_BIG)
-		regs->msr &= ~MSR_LE;
+		regs_set_return_msr(regs, regs->msr & ~MSR_LE);
 	else if (val == PR_ENDIAN_LITTLE || val == PR_ENDIAN_PPC_LITTLE)
-		regs->msr |= MSR_LE;
+		regs_set_return_msr(regs, regs->msr | MSR_LE);
 	else
 		return -EINVAL;