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| author | Sam bobroff <sam.bobroff@au1.ibm.com> | 2015-06-12 04:06:32 +0300 |
|---|---|---|
| committer | Michael Ellerman <mpe@ellerman.id.au> | 2015-06-19 10:10:28 +0300 |
| commit | b4b56f9ecab40f3b4ef53e130c9f6663be491894 (patch) | |
| tree | fb469b542c15a246790eca454d405bef3dc2c227 /arch/powerpc/kernel/entry_64.S | |
| parent | b5926430dfa07d17e5d768c16b0d81c13a793f7c (diff) | |
| download | linux-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/kernel/entry_64.S')
| -rw-r--r-- | arch/powerpc/kernel/entry_64.S | 35 |
1 files changed, 35 insertions, 0 deletions
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S index 278888e89acc..579e0f9a2d57 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) |