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Groups > linux.kernel > #1233594
| From | Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | [PATCH 4.2 028/134] arm64: entry: always restore x0 from the stack on syscall return |
| Date | 2015-09-27 00:30 +0200 |
| Message-ID | <qd68G-4RL-31@gated-at.bofh.it> (permalink) |
| References | <qd4Jz-2Ha-3@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
4.2-stable review patch. If anyone has any objections, please let me know. ------------------ From: Will Deacon <will.deacon@arm.com> commit 412fcb6cebd758d080cacd5a41a0cbc656ea5fce upstream. We have a micro-optimisation on the fast syscall return path where we take care to keep x0 live with the return value from the syscall so that we can avoid restoring it from the stack. The benefit of doing this is fairly suspect, since we will be restoring x1 from the stack anyway (which lives adjacent in the pt_regs structure) and the only additional cost is saving x0 back to pt_regs after the syscall handler, which could be seen as a poor man's prefetch. More importantly, this causes issues with the context tracking code. The ct_user_enter macro ends up branching into C code, which is free to use x0 as a scratch register and consequently leads to us returning junk back to userspace as the syscall return value. Rather than special case the context-tracking code, this patch removes the questionable optimisation entirely. Cc: Larry Bassel <larry.bassel@linaro.org> Cc: Kevin Hilman <khilman@linaro.org> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Reported-by: Hanjun Guo <hanjun.guo@linaro.org> Tested-by: Hanjun Guo <hanjun.guo@linaro.org> Signed-off-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> --- arch/arm64/kernel/entry.S | 17 ++++++----------- 1 file changed, 6 insertions(+), 11 deletions(-) --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -116,7 +116,7 @@ */ .endm - .macro kernel_exit, el, ret = 0 + .macro kernel_exit, el ldp x21, x22, [sp, #S_PC] // load ELR, SPSR .if \el == 0 ct_user_enter @@ -146,11 +146,7 @@ .endif msr elr_el1, x21 // set up the return data msr spsr_el1, x22 - .if \ret - ldr x1, [sp, #S_X1] // preserve x0 (syscall return) - .else ldp x0, x1, [sp, #16 * 0] - .endif ldp x2, x3, [sp, #16 * 1] ldp x4, x5, [sp, #16 * 2] ldp x6, x7, [sp, #16 * 3] @@ -613,22 +609,21 @@ ENDPROC(cpu_switch_to) */ ret_fast_syscall: disable_irq // disable interrupts + str x0, [sp, #S_X0] // returned x0 ldr x1, [tsk, #TI_FLAGS] // re-check for syscall tracing and x2, x1, #_TIF_SYSCALL_WORK cbnz x2, ret_fast_syscall_trace and x2, x1, #_TIF_WORK_MASK - cbnz x2, fast_work_pending + cbnz x2, work_pending enable_step_tsk x1, x2 - kernel_exit 0, ret = 1 + kernel_exit 0 ret_fast_syscall_trace: enable_irq // enable interrupts - b __sys_trace_return + b __sys_trace_return_skipped // we already saved x0 /* * Ok, we need to do extra processing, enter the slow path. */ -fast_work_pending: - str x0, [sp, #S_X0] // returned x0 work_pending: tbnz x1, #TIF_NEED_RESCHED, work_resched /* TIF_SIGPENDING, TIF_NOTIFY_RESUME or TIF_FOREIGN_FPSTATE case */ @@ -652,7 +647,7 @@ ret_to_user: cbnz x2, work_pending enable_step_tsk x1, x2 no_work_pending: - kernel_exit 0, ret = 0 + kernel_exit 0 ENDPROC(ret_to_user) /* -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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[PATCH 4.2 000/134] 4.2.2-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 00:20 +0200
[PATCH 4.2 049/134] powerpc/eeh: Probe after unbalanced kref check Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 00:20 +0200
[PATCH 4.2 018/134] MIPS: CPS: use 32b accesses to GCRs Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 00:20 +0200
[PATCH 4.2 032/134] arm64: compat: fix vfp save/restore across signal handlers in big-endian Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 00:20 +0200
[PATCH 4.2 047/134] pinctrl: at91: fix null pointer dereference Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 00:20 +0200
[PATCH 4.2 006/134] nfc: st-nci: Remove data from ack_pending_q when receiving a SYNC_ACK Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 00:20 +0200
[PATCH 4.2 015/134] rtlwifi: rtl8821ae: Fix an expression that is always false Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 00:20 +0200
[PATCH 4.2 030/134] of/fdt: make memblock maximum physical address arch configurable Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 00:20 +0200
[PATCH 4.2 035/134] arm/arm64: KVM: vgic: Check for !irqchip_in_kernel() when mapping resources Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 00:20 +0200
[PATCH 4.2 050/134] powerpc/eeh: Fix fenced PHB caused by eeh_slot_error_detail() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 00:20 +0200
[PATCH 4.2 007/134] nfc: st-nci: Free data with irrelevant NDLC PCB_SYNC value Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 00:20 +0200
[PATCH 4.2 017/134] tg3: Fix temperature reporting Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 00:20 +0200
[PATCH 4.2 053/134] powerpc: Uncomment and make enable_kernel_vsx() routine available Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 00:20 +0200
[PATCH 4.2 003/134] nfc: st-nci: Fix non accurate comment for st_nci_i2c_read Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 00:20 +0200
[PATCH 4.2 036/134] KVM: arm64: add workaround for Cortex-A57 erratum #852523 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 00:20 +0200
[PATCH 4.2 004/134] NFC: st21nfca: fix use of uninitialized variables in error path Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 00:20 +0200
[PATCH 4.2 037/134] arm64: KVM: Disable virtual timer even if the guest is not using it Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 00:20 +0200
[PATCH 4.2 008/134] nfc: netlink: Add check on NFC_ATTR_VENDOR_DATA Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 00:20 +0200
[PATCH 4.2 048/134] powerpc/pseries: Fix corrupted pdn list Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 00:20 +0200
[PATCH 4.2 059/134] powerpc/mm: Recompute hash value after a failed update Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 00:20 +0200
[PATCH 4.2 021/134] mac80211: enable assoc check for mesh interfaces Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 00:30 +0200
[PATCH 4.2 029/134] arm64: flush FP/SIMD state correctly after execve() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 00:30 +0200
[PATCH 4.2 019/134] MIPS: math-emu: Allow m{f,t}hc emulation on MIPS R6 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 00:30 +0200
[PATCH 4.2 024/134] cxl: Fix unbalanced pci_dev_get in cxl_probe Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 00:30 +0200
[PATCH 4.2 002/134] nfc: st-nci: Fix typo when changing from st21nfcb to st-nci Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 00:30 +0200
[PATCH 4.2 022/134] cxl: Allow release of contexts which have been OPENED but not STARTED Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 00:30 +0200
[PATCH 4.2 027/134] arm64: kconfig: Move LIST_POISON to a safe value Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 00:30 +0200
[PATCH 4.2 020/134] MIPS: math-emu: Emulate missing BC1{EQ,NE}Z instructions Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 00:30 +0200
[PATCH 4.2 025/134] ext4: dont manipulate recovery flag when freezing no-journal fs Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 00:30 +0200
[PATCH 4.2 028/134] arm64: entry: always restore x0 from the stack on syscall return Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 00:30 +0200
[PATCH 4.2 010/134] nfc: nci: hci: Add check on skb nci_hci_send_cmd parameter Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 00:30 +0200
[PATCH 4.2 026/134] Revert "ext4: remove block_device_ejected" Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 00:30 +0200
[PATCH 4.2 023/134] cxl: Remove racy attempt to force EEH invocation in reset Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 00:30 +0200
Re: [PATCH 4.2 000/134] 4.2.2-stable review Guenter Roeck <linux@roeck-us.net> - 2015-09-27 20:20 +0200
Re: [PATCH 4.2 000/134] 4.2.2-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-27 20:40 +0200
Re: [PATCH 4.2 000/134] 4.2.2-stable review Sudip Mukherjee <sudipm.mukherjee@gmail.com> - 2015-09-28 08:00 +0200
Re: [PATCH 4.2 000/134] 4.2.2-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-09-28 16:30 +0200
Re: [PATCH 4.2 000/134] 4.2.2-stable review Sudip Mukherjee <sudipm.mukherjee@gmail.com> - 2015-09-28 17:10 +0200
Re: [PATCH 4.2 000/134] 4.2.2-stable review Guenter Roeck <linux@roeck-us.net> - 2015-09-28 17:10 +0200
Re: [PATCH 4.2 000/134] 4.2.2-stable review Shuah Khan <shuahkh@osg.samsung.com> - 2015-09-28 19:40 +0200
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