[PATCH v3 06/22] powerpc/32s: Do kuep_lock() and kuep_unlock() in assembly

From: Christophe Leroy
Date: Tue Oct 19 2021 - 03:30:13 EST

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When interrupt and syscall entries where converted to C, KUEP locking
and unlocking was also converted. It improved performance by unrolling
the loop, and allowed easily implementing boot time deactivation of
KUEP.

However, null_syscall selftest shows that KUEP is still heavy
(361 cycles with KUEP, 212 cycles without).

A way to improve more is to group 'mtsr's together, instead of
repeating 'addi' + 'mtsr' several times.

In order to do that, more registers need to be available. In C, GCC
will always be able to provide the requested number of registers, but
at the cost of saving some data on the stack, which is counter
performant here.

So let's do it in assembly, when we have full control of which
register can be used. It also has the advantage of locking earlier
and unlocking later and it helps GCC generating less tricky code.
The only drawback is to make boot time deactivation less straight
forward and require 'hand' instruction patching.

Group 'mtsr's by 4.

With this change, null_syscall selftest reports 336 cycles. Without
the change it was 361 cycles, that's a 7% reduction.

Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
---
arch/powerpc/include/asm/book3s/32/kup.h | 34 --------
arch/powerpc/include/asm/book3s/32/mmu-hash.h | 77 ++++++++++++++++++-
arch/powerpc/include/asm/interrupt.h | 6 +-
arch/powerpc/include/asm/kup.h | 5 --
arch/powerpc/kernel/entry_32.S | 31 ++++++++
arch/powerpc/kernel/head_32.h | 6 ++
arch/powerpc/kernel/head_book3s_32.S | 4 +
arch/powerpc/kernel/interrupt.c | 3 -
arch/powerpc/mm/book3s32/kuep.c | 2 -
9 files changed, 119 insertions(+), 49 deletions(-)

diff --git a/arch/powerpc/include/asm/book3s/32/kup.h b/arch/powerpc/include/asm/book3s/32/kup.h
index fb6c39225dd1..e3db5ed4b255 100644
--- a/arch/powerpc/include/asm/book3s/32/kup.h
+++ b/arch/powerpc/include/asm/book3s/32/kup.h
@@ -23,40 +23,6 @@ static __always_inline bool kuep_is_disabled(void)
return !IS_ENABLED(CONFIG_PPC_KUEP);
}

-static inline void kuep_lock(void)
-{
- if (kuep_is_disabled())
- return;
-
- update_user_segments(mfsr(0) | SR_NX);
- /*
- * This isync() shouldn't be necessary as the kernel is not excepted to
- * run any instruction in userspace soon after the update of segments,
- * but hash based cores (at least G3) seem to exhibit a random
- * behaviour when the 'isync' is not there. 603 cores don't have this
- * behaviour so don't do the 'isync' as it saves several CPU cycles.
- */
- if (mmu_has_feature(MMU_FTR_HPTE_TABLE))
- isync(); /* Context sync required after mtsr() */
-}
-
-static inline void kuep_unlock(void)
-{
- if (kuep_is_disabled())
- return;
-
- update_user_segments(mfsr(0) & ~SR_NX);
- /*
- * This isync() shouldn't be necessary as a 'rfi' will soon be executed
- * to return to userspace, but hash based cores (at least G3) seem to
- * exhibit a random behaviour when the 'isync' is not there. 603 cores
- * don't have this behaviour so don't do the 'isync' as it saves several
- * CPU cycles.
- */
- if (mmu_has_feature(MMU_FTR_HPTE_TABLE))
- isync(); /* Context sync required after mtsr() */
-}
-
#ifdef CONFIG_PPC_KUAP

#include <linux/sched.h>
diff --git a/arch/powerpc/include/asm/book3s/32/mmu-hash.h b/arch/powerpc/include/asm/book3s/32/mmu-hash.h
index f5be185cbdf8..e2f7ccc13edb 100644
--- a/arch/powerpc/include/asm/book3s/32/mmu-hash.h
+++ b/arch/powerpc/include/asm/book3s/32/mmu-hash.h
@@ -64,7 +64,82 @@ struct ppc_bat {
#define SR_KP 0x20000000 /* User key */
#define SR_KS 0x40000000 /* Supervisor key */

-#ifndef __ASSEMBLY__
+#ifdef __ASSEMBLY__
+
+#include <asm/asm-offsets.h>
+
+.macro uus_addi sr reg1 reg2 imm
+ .if NUM_USER_SEGMENTS > \sr
+ addi \reg1,\reg2,\imm
+ .endif
+.endm
+
+.macro uus_mtsr sr reg1
+ .if NUM_USER_SEGMENTS > \sr
+ mtsr \sr, \reg1
+ .endif
+.endm
+
+/*
+ * This isync() shouldn't be necessary as the kernel is not excepted to run
+ * any instruction in userspace soon after the update of segments and 'rfi'
+ * instruction is used to return to userspace, but hash based cores
+ * (at least G3) seem to exhibit a random behaviour when the 'isync' is not
+ * there. 603 cores don't have this behaviour so don't do the 'isync' as it
+ * saves several CPU cycles.
+ */
+.macro uus_isync
+#ifdef CONFIG_PPC_BOOK3S_604
+BEGIN_MMU_FTR_SECTION
+ isync
+END_MMU_FTR_SECTION_IFSET(MMU_FTR_HPTE_TABLE)
+#endif
+.endm
+
+.macro update_user_segments_by_4 tmp1 tmp2 tmp3 tmp4
+ uus_addi 1, \tmp2, \tmp1, 0x111
+ uus_addi 2, \tmp3, \tmp1, 0x222
+ uus_addi 3, \tmp4, \tmp1, 0x333
+
+ uus_mtsr 0, \tmp1
+ uus_mtsr 1, \tmp2
+ uus_mtsr 2, \tmp3
+ uus_mtsr 3, \tmp4
+
+ uus_addi 4, \tmp1, \tmp1, 0x444
+ uus_addi 5, \tmp2, \tmp2, 0x444
+ uus_addi 6, \tmp3, \tmp3, 0x444
+ uus_addi 7, \tmp4, \tmp4, 0x444
+
+ uus_mtsr 4, \tmp1
+ uus_mtsr 5, \tmp2
+ uus_mtsr 6, \tmp3
+ uus_mtsr 7, \tmp4
+
+ uus_addi 8, \tmp1, \tmp1, 0x444
+ uus_addi 9, \tmp2, \tmp2, 0x444
+ uus_addi 10, \tmp3, \tmp3, 0x444
+ uus_addi 11, \tmp4, \tmp4, 0x444
+
+ uus_mtsr 8, \tmp1
+ uus_mtsr 9, \tmp2
+ uus_mtsr 10, \tmp3
+ uus_mtsr 11, \tmp4
+
+ uus_addi 12, \tmp1, \tmp1, 0x444
+ uus_addi 13, \tmp2, \tmp2, 0x444
+ uus_addi 14, \tmp3, \tmp3, 0x444
+ uus_addi 15, \tmp4, \tmp4, 0x444
+
+ uus_mtsr 12, \tmp1
+ uus_mtsr 13, \tmp2
+ uus_mtsr 14, \tmp3
+ uus_mtsr 15, \tmp4
+
+ uus_isync
+.endm
+
+#else

/*
* This macro defines the mapping from contexts to VSIDs (virtual
diff --git a/arch/powerpc/include/asm/interrupt.h b/arch/powerpc/include/asm/interrupt.h
index a1d238255f07..3bbca1fbbe1e 100644
--- a/arch/powerpc/include/asm/interrupt.h
+++ b/arch/powerpc/include/asm/interrupt.h
@@ -139,12 +139,10 @@ static inline void interrupt_enter_prepare(struct pt_regs *regs, struct interrup
if (!arch_irq_disabled_regs(regs))
trace_hardirqs_off();

- if (user_mode(regs)) {
- kuep_lock();
+ if (user_mode(regs))
account_cpu_user_entry();
- } else {
+ else
kuap_save_and_lock(regs);
- }
#endif

#ifdef CONFIG_PPC64
diff --git a/arch/powerpc/include/asm/kup.h b/arch/powerpc/include/asm/kup.h
index 8699ca5884b9..94734a8eb54d 100644
--- a/arch/powerpc/include/asm/kup.h
+++ b/arch/powerpc/include/asm/kup.h
@@ -40,11 +40,6 @@ void setup_kuep(bool disabled);
static inline void setup_kuep(bool disabled) { }
#endif /* CONFIG_PPC_KUEP */

-#ifndef CONFIG_PPC_BOOK3S_32
-static inline void kuep_lock(void) { }
-static inline void kuep_unlock(void) { }
-#endif
-
#ifdef CONFIG_PPC_KUAP
void setup_kuap(bool disabled);
#else
diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index 61fdd53cdd9a..4ba6a8c43475 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -73,6 +73,34 @@ prepare_transfer_to_handler:
_ASM_NOKPROBE_SYMBOL(prepare_transfer_to_handler)
#endif /* CONFIG_PPC_BOOK3S_32 || CONFIG_E500 */

+#if defined(CONFIG_PPC_KUEP) && defined(CONFIG_PPC_BOOK3S_32)
+ .globl __kuep_lock
+__kuep_lock:
+ mfsr r9,0
+ rlwinm r9,r9,0,8,3
+ oris r9,r9,SR_NX@h
+ update_user_segments_by_4 r9, r10, r11, r12
+ blr
+
+__kuep_unlock:
+ mfsr r9,0
+ rlwinm r9,r9,0,8,2
+ update_user_segments_by_4 r9, r10, r11, r12
+ blr
+
+.macro kuep_lock
+ bl __kuep_lock
+.endm
+.macro kuep_unlock
+ bl __kuep_unlock
+.endm
+#else
+.macro kuep_lock
+.endm
+.macro kuep_unlock
+.endm
+#endif
+
.globl transfer_to_syscall
transfer_to_syscall:
stw r11, GPR1(r1)
@@ -94,6 +122,7 @@ transfer_to_syscall:
SAVE_2GPRS(7, r1)
addi r2,r10,-THREAD
SAVE_NVGPRS(r1)
+ kuep_lock

/* Calling convention has r9 = orig r0, r10 = regs */
addi r10,r1,STACK_FRAME_OVERHEAD
@@ -110,6 +139,7 @@ ret_from_syscall:
cmplwi cr0,r5,0
bne- 2f
#endif /* CONFIG_PPC_47x */
+ kuep_unlock
lwz r4,_LINK(r1)
lwz r5,_CCR(r1)
mtlr r4
@@ -273,6 +303,7 @@ interrupt_return:
beq .Lkernel_interrupt_return
bl interrupt_exit_user_prepare
cmpwi r3,0
+ kuep_unlock
bne- .Lrestore_nvgprs

.Lfast_user_interrupt_return:
diff --git a/arch/powerpc/kernel/head_32.h b/arch/powerpc/kernel/head_32.h
index 6b1ec9e3541b..133197039775 100644
--- a/arch/powerpc/kernel/head_32.h
+++ b/arch/powerpc/kernel/head_32.h
@@ -136,6 +136,12 @@ _ASM_NOKPROBE_SYMBOL(\name\()_virt)
andi. r12,r9,MSR_PR
bne 777f
bl prepare_transfer_to_handler
+#ifdef CONFIG_PPC_KUEP
+ b 778f
+777:
+ bl __kuep_lock
+778:
+#endif
777:
#endif
.endm
diff --git a/arch/powerpc/kernel/head_book3s_32.S b/arch/powerpc/kernel/head_book3s_32.S
index 68e5c0a7e99d..fa84744d6b24 100644
--- a/arch/powerpc/kernel/head_book3s_32.S
+++ b/arch/powerpc/kernel/head_book3s_32.S
@@ -931,7 +931,11 @@ END_MMU_FTR_SECTION_IFSET(MMU_FTR_USE_HIGH_BATS)
_GLOBAL(load_segment_registers)
li r0, NUM_USER_SEGMENTS /* load up user segment register values */
mtctr r0 /* for context 0 */
+#ifdef CONFIG_PPC_KUEP
+ lis r3, SR_NX@h /* Kp = 0, Ks = 0, VSID = 0 */
+#else
li r3, 0 /* Kp = 0, Ks = 0, VSID = 0 */
+#endif
li r4, 0
3: mtsrin r3, r4
addi r3, r3, 0x111 /* increment VSID */
diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
index de10a2697258..0d12aa66e1f9 100644
--- a/arch/powerpc/kernel/interrupt.c
+++ b/arch/powerpc/kernel/interrupt.c
@@ -81,8 +81,6 @@ notrace long system_call_exception(long r3, long r4, long r5,
{
syscall_fn f;

- kuep_lock();
-
regs->orig_gpr3 = r3;

if (IS_ENABLED(CONFIG_PPC_IRQ_SOFT_MASK_DEBUG))
@@ -406,7 +404,6 @@ interrupt_exit_user_prepare_main(unsigned long ret, struct pt_regs *regs)

/* Restore user access locks last */
kuap_user_restore(regs);
- kuep_unlock();

return ret;
}
diff --git a/arch/powerpc/mm/book3s32/kuep.c b/arch/powerpc/mm/book3s32/kuep.c
index 8474edce3df9..bac1420d028b 100644
--- a/arch/powerpc/mm/book3s32/kuep.c
+++ b/arch/powerpc/mm/book3s32/kuep.c
@@ -5,8 +5,6 @@

void setup_kuep(bool disabled)
{
- kuep_lock();
-
if (smp_processor_id() != boot_cpuid)
return;

--
2.31.1

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