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authorSam bobroff <sam.bobroff@au1.ibm.com>2015-06-12 01:06:32 (GMT)
committerMichael Ellerman <mpe@ellerman.id.au>2015-06-19 07:10:28 (GMT)
commitb4b56f9ecab40f3b4ef53e130c9f6663be491894 (patch)
treefb469b542c15a246790eca454d405bef3dc2c227 /arch/powerpc
parentb5926430dfa07d17e5d768c16b0d81c13a793f7c (diff)
downloadlinux-b4b56f9ecab40f3b4ef53e130c9f6663be491894.tar.xz
powerpc/tm: Abort syscalls in active transactions
This patch changes the syscall handler to doom (tabort) active transactions when a syscall is made and return very early without performing the syscall and keeping side effects to a minimum (no CPU accounting or system call tracing is performed). Also included is a new HWCAP2 bit, PPC_FEATURE2_HTM_NOSC, to indicate this behaviour to userspace. Currently, the system call instruction automatically suspends an active transaction which causes side effects to persist when an active transaction fails. This does change the kernel's behaviour, but in a way that was documented as unsupported. It doesn't reduce functionality as syscalls will still be performed after tsuspend; it just requires that the transaction be explicitly suspended. It also provides a consistent interface and makes the behaviour of user code substantially the same across powerpc and platforms that do not support suspended transactions (e.g. x86 and s390). Performance measurements using http://ozlabs.org/~anton/junkcode/null_syscall.c indicate the cost of a normal (non-aborted) system call increases by about 0.25%. Signed-off-by: Sam Bobroff <sam.bobroff@au1.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Diffstat (limited to 'arch/powerpc')
-rw-r--r--arch/powerpc/include/asm/cputable.h10
-rw-r--r--arch/powerpc/include/uapi/asm/cputable.h1
-rw-r--r--arch/powerpc/include/uapi/asm/tm.h2
-rw-r--r--arch/powerpc/kernel/cputable.c4
-rw-r--r--arch/powerpc/kernel/entry_64.S35
5 files changed, 46 insertions, 6 deletions
diff --git a/arch/powerpc/include/asm/cputable.h b/arch/powerpc/include/asm/cputable.h
index 6367b83..4994648 100644
--- a/arch/powerpc/include/asm/cputable.h
+++ b/arch/powerpc/include/asm/cputable.h
@@ -242,11 +242,13 @@ enum {
/* We only set the TM feature if the kernel was compiled with TM supprt */
#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
-#define CPU_FTR_TM_COMP CPU_FTR_TM
-#define PPC_FEATURE2_HTM_COMP PPC_FEATURE2_HTM
+#define CPU_FTR_TM_COMP CPU_FTR_TM
+#define PPC_FEATURE2_HTM_COMP PPC_FEATURE2_HTM
+#define PPC_FEATURE2_HTM_NOSC_COMP PPC_FEATURE2_HTM_NOSC
#else
-#define CPU_FTR_TM_COMP 0
-#define PPC_FEATURE2_HTM_COMP 0
+#define CPU_FTR_TM_COMP 0
+#define PPC_FEATURE2_HTM_COMP 0
+#define PPC_FEATURE2_HTM_NOSC_COMP 0
#endif
/* We need to mark all pages as being coherent if we're SMP or we have a
diff --git a/arch/powerpc/include/uapi/asm/cputable.h b/arch/powerpc/include/uapi/asm/cputable.h
index de2c0e4..4368604 100644
--- a/arch/powerpc/include/uapi/asm/cputable.h
+++ b/arch/powerpc/include/uapi/asm/cputable.h
@@ -42,5 +42,6 @@
#define PPC_FEATURE2_ISEL 0x08000000
#define PPC_FEATURE2_TAR 0x04000000
#define PPC_FEATURE2_VEC_CRYPTO 0x02000000
+#define PPC_FEATURE2_HTM_NOSC 0x01000000
#endif /* _UAPI__ASM_POWERPC_CPUTABLE_H */
diff --git a/arch/powerpc/include/uapi/asm/tm.h b/arch/powerpc/include/uapi/asm/tm.h
index 5d836b7..5047659 100644
--- a/arch/powerpc/include/uapi/asm/tm.h
+++ b/arch/powerpc/include/uapi/asm/tm.h
@@ -11,7 +11,7 @@
#define TM_CAUSE_RESCHED 0xde
#define TM_CAUSE_TLBI 0xdc
#define TM_CAUSE_FAC_UNAV 0xda
-#define TM_CAUSE_SYSCALL 0xd8 /* future use */
+#define TM_CAUSE_SYSCALL 0xd8
#define TM_CAUSE_MISC 0xd6 /* future use */
#define TM_CAUSE_SIGNAL 0xd4
#define TM_CAUSE_ALIGNMENT 0xd2
diff --git a/arch/powerpc/kernel/cputable.c b/arch/powerpc/kernel/cputable.c
index 60262fd..7d80bfd 100644
--- a/arch/powerpc/kernel/cputable.c
+++ b/arch/powerpc/kernel/cputable.c
@@ -108,7 +108,9 @@ extern void __restore_cpu_e6500(void);
PPC_FEATURE_TRUE_LE | \
PPC_FEATURE_PSERIES_PERFMON_COMPAT)
#define COMMON_USER2_POWER8 (PPC_FEATURE2_ARCH_2_07 | \
- PPC_FEATURE2_HTM_COMP | PPC_FEATURE2_DSCR | \
+ PPC_FEATURE2_HTM_COMP | \
+ PPC_FEATURE2_HTM_NOSC_COMP | \
+ PPC_FEATURE2_DSCR | \
PPC_FEATURE2_ISEL | PPC_FEATURE2_TAR | \
PPC_FEATURE2_VEC_CRYPTO)
#define COMMON_USER_PA6T (COMMON_USER_PPC64 | PPC_FEATURE_PA6T |\
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 278888e..579e0f9 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -34,6 +34,7 @@
#include <asm/ftrace.h>
#include <asm/hw_irq.h>
#include <asm/context_tracking.h>
+#include <asm/tm.h>
/*
* System calls.
@@ -51,6 +52,12 @@ exception_marker:
.globl system_call_common
system_call_common:
+#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
+BEGIN_FTR_SECTION
+ extrdi. r10, r12, 1, (63-MSR_TS_T_LG) /* transaction active? */
+ bne tabort_syscall
+END_FTR_SECTION_IFSET(CPU_FTR_TM)
+#endif
andi. r10,r12,MSR_PR
mr r10,r1
addi r1,r1,-INT_FRAME_SIZE
@@ -311,6 +318,34 @@ syscall_exit_work:
bl do_syscall_trace_leave
b ret_from_except
+#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
+tabort_syscall:
+ /* Firstly we need to enable TM in the kernel */
+ mfmsr r10
+ li r13, 1
+ rldimi r10, r13, MSR_TM_LG, 63-MSR_TM_LG
+ mtmsrd r10, 0
+
+ /* tabort, this dooms the transaction, nothing else */
+ li r13, (TM_CAUSE_SYSCALL|TM_CAUSE_PERSISTENT)
+ TABORT(R13)
+
+ /*
+ * Return directly to userspace. We have corrupted user register state,
+ * but userspace will never see that register state. Execution will
+ * resume after the tbegin of the aborted transaction with the
+ * checkpointed register state.
+ */
+ li r13, MSR_RI
+ andc r10, r10, r13
+ mtmsrd r10, 1
+ mtspr SPRN_SRR0, r11
+ mtspr SPRN_SRR1, r12
+
+ rfid
+ b . /* prevent speculative execution */
+#endif
+
/* Save non-volatile GPRs, if not already saved. */
_GLOBAL(save_nvgprs)
ld r11,_TRAP(r1)