[PATCH Vivid SRU] powerpc/tm: backport b4b56f to Abort syscalls in active transactions
tim.gardner at canonical.com
tim.gardner at canonical.com
Sun May 8 23:17:24 UTC 2016
From: Simon Guo <simonguo at linux.vnet.ibm.com>
BugLink: http://bugs.launchpad.net/bugs/1572624
This patch backport b4b56f9ecab40f3b to Ubuntu 14.04.04.
quoted from original commit:
It is about changing 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.
Without this backport patch, app running TM testing on Ubuntu 14.04
might hang. Glibc with TLE enabled will be able to bypass this issue.
However it is not enabled on Ubunt 14.04.
The issue to be addressed:
User is creating stack structure using C++ transactional memory
extension:
int Pop(int)
{
int ret = 0;
__transaction_atomic
{
if(!stack_.empty())
{
ret = stack_.top();
stack_.pop();
} else
ret = -1;
}
return ret;
}
While evaluating if(!stack_.empty()), this code calls a libitm function
(GCC code), which calls malloc (glibc code) which ends up calling futex
(a syscall).
A syscall inside a transaction is forbidden by the kernel, but there is
nothing the user can do to avoid this syscall.
This will hang the user application inside the malloc(), which would be
waiting for the futex to return.
Ubuntu 14.04 provides glibc 2.19, which is too old to know about HTM.
And this is probably happening with other libraries as well.
Signed-off-by: Simon Guo <simonguo at linux.vnet.ibm.com>
Signed-off-by: Tim Gardner <tim.gardner at canonical.com>
---
Documentation/powerpc/transactional_memory.txt | 32 +++++++++++------------
arch/powerpc/include/asm/cputable.h | 10 +++++---
arch/powerpc/include/uapi/asm/cputable.h | 1 +
arch/powerpc/include/uapi/asm/tm.h | 2 +-
arch/powerpc/kernel/cputable.c | 4 ++-
arch/powerpc/kernel/entry_64.S | 35 ++++++++++++++++++++++++++
6 files changed, 62 insertions(+), 22 deletions(-)
diff --git a/Documentation/powerpc/transactional_memory.txt b/Documentation/powerpc/transactional_memory.txt
index 9791e98..98b39af 100644
--- a/Documentation/powerpc/transactional_memory.txt
+++ b/Documentation/powerpc/transactional_memory.txt
@@ -74,22 +74,23 @@ Causes of transaction aborts
Syscalls
========
-Performing syscalls from within transaction is not recommended, and can lead
-to unpredictable results.
+Syscalls made from within an active transaction will not be performed and the
+transaction will be doomed by the kernel with the failure code TM_CAUSE_SYSCALL
+| TM_CAUSE_PERSISTENT.
-Syscalls do not by design abort transactions, but beware: The kernel code will
-not be running in transactional state. The effect of syscalls will always
-remain visible, but depending on the call they may abort your transaction as a
-side-effect, read soon-to-be-aborted transactional data that should not remain
-invisible, etc. If you constantly retry a transaction that constantly aborts
-itself by calling a syscall, you'll have a livelock & make no progress.
+Syscalls made from within a suspended transaction are performed as normal and
+the transaction is not explicitly doomed by the kernel. However, what the
+kernel does to perform the syscall may result in the transaction being doomed
+by the hardware. The syscall is performed in suspended mode so any side
+effects will be persistent, independent of transaction success or failure. No
+guarantees are provided by the kernel about which syscalls will affect
+transaction success.
-Simple syscalls (e.g. sigprocmask()) "could" be OK. Even things like write()
-from, say, printf() should be OK as long as the kernel does not access any
-memory that was accessed transactionally.
-
-Consider any syscalls that happen to work as debug-only -- not recommended for
-production use. Best to queue them up till after the transaction is over.
+Care must be taken when relying on syscalls to abort during active transactions
+if the calls are made via a library. Libraries may cache values (which may
+give the appearance of success) or perform operations that cause transaction
+failure before entering the kernel (which may produce different failure codes).
+Examples are glibc's getpid() and lazy symbol resolution.
Signals
@@ -176,8 +177,7 @@ kernel aborted a transaction:
TM_CAUSE_RESCHED Thread was rescheduled.
TM_CAUSE_TLBI Software TLB invalide.
TM_CAUSE_FAC_UNAV FP/VEC/VSX unavailable trap.
- TM_CAUSE_SYSCALL Currently unused; future syscalls that must abort
- transactions for consistency will use this.
+ TM_CAUSE_SYSCALL Syscall from active transaction.
TM_CAUSE_SIGNAL Signal delivered.
TM_CAUSE_MISC Currently unused.
TM_CAUSE_ALIGNMENT Alignment fault.
diff --git a/arch/powerpc/include/asm/cputable.h b/arch/powerpc/include/asm/cputable.h
index 22d5a7d..4ec19da 100644
--- a/arch/powerpc/include/asm/cputable.h
+++ b/arch/powerpc/include/asm/cputable.h
@@ -236,11 +236,13 @@ extern const char *powerpc_base_platform;
/* 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 67de80a..2734c00 100644
--- a/arch/powerpc/include/uapi/asm/cputable.h
+++ b/arch/powerpc/include/uapi/asm/cputable.h
@@ -43,5 +43,6 @@
#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 c18a2ea..bf3eb39 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 1d8b58a..0dce87f 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)
--
1.9.1
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