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Subject: Re: [PATCH v13 00/10] powerpc: Switch to CONFIG_THREAD_INFO_IN_TASK
From:   Christophe Leroy <christophe.leroy@c-s.fr>
To:     Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Nicholas Piggin <npiggin@gmail.com>
Cc:     Mike Rapoport <rppt@linux.ibm.com>, linuxppc-dev@lists.ozlabs.org,
        linux-kernel@vger.kernel.org
References: <cover.1547195976.git.christophe.leroy@c-s.fr>
Message-ID: <2e700e1c-5bd9-652e-b535-68a89dd703a1@c-s.fr>
Date:   Wed, 23 Jan 2019 11:04:16 +0100
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Le 12/01/2019 à 10:55, Christophe Leroy a écrit :
> The purpose of this serie is to activate CONFIG_THREAD_INFO_IN_TASK which
> moves the thread_info into task_struct.
> 
> Moving thread_info into task_struct has the following advantages:
> - It protects thread_info from corruption in the case of stack
> overflows.
> - Its address is harder to determine if stack addresses are
> leaked, making a number of attacks more difficult.

I ran null_syscall and context_switch benchmark selftests and the result 
is surprising. There is slight degradation in context_switch and a 
significant one on null_syscall:

Without the serie:

~# chrt -f 98 ./context_switch --no-altivec --no-vector --no-fp
55542
55562
55564
55562
55568
...

~# ./null_syscall
    2546.71 ns     336.17 cycles


With the serie:

~# chrt -f 98 ./context_switch --no-altivec --no-vector --no-fp
55138
55142
55152
55144
55142

~# ./null_syscall
    3479.54 ns     459.30 cycles

So 0,8% less context switches per second and 37% more time for one syscall ?


Any idea ?

Christophe


> 
> Changes since v12:
>   - Patch 1: Taken comment from Mike (re-introduced the 'panic' in case memblock allocation fails in setup_64.c
>   - Patch 1: Added alloc_stack() function in setup_32.c to also panic in case of allocation failure.
> 
> Changes since v11:
>   - Rebased on 81775f5563fa ("Automatic merge of branches 'master', 'next' and 'fixes' into merge")
>   - Added a first patch to change memblock allocs to functions returning virtual addrs. This removes
>     the memset() which were the only remaining stuff in irq_ctx_init() and exc_lvl_ctx_init() at the end.
>   - dropping irq_ctx_init() and exc_lvl_ctx_init() in patch 5 (powerpc: Activate CONFIG_THREAD_INFO_IN_TASK)
>   - A few cosmetic changes in commit log and code.
> 
> Changes since v10:
>   - Rebased on 21622a0d2023 ("Automatic merge of branches 'master', 'next' and 'fixes' into merge")
>    ==> Fixed conflict in setup_32.S
> 
> Changes since v9:
>   - Rebased on 183cbf93be88 ("Automatic merge of branches 'master', 'next' and 'fixes' into merge")
>    ==> Fixed conflict on xmon
> 
> Changes since v8:
>   - Rebased on e589b79e40d9 ("Automatic merge of branches 'master', 'next' and 'fixes' into merge")
>    ==> Main impact was conflicts due to commit 9a8dd708d547 ("memblock: rename memblock_alloc{_nid,_try_nid} to memblock_phys_alloc*")
> 
> Changes since v7:
>   - Rebased on fb6c6ce7907d ("Automatic merge of branches 'master', 'next' and 'fixes' into merge")
> 
> Changes since v6:
>   - Fixed validate_sp() to exclude NULL sp in 'regain entire stack space' patch (early crash with CONFIG_KMEMLEAK)
> 
> Changes since v5:
>   - Fixed livepatch_sp setup by using end_of_stack() instead of hardcoding
>   - Fixed PPC_BPF_LOAD_CPU() macro
> 
> Changes since v4:
>   - Fixed a build failure on 32bits SMP when include/generated/asm-offsets.h is not
>   already existing, was due to spaces instead of a tab in the Makefile
> 
> Changes since RFC v3: (based on Nick's review)
>   - Renamed task_size.h to task_size_user64.h to better relate to what it contains.
>   - Handling of the isolation of thread_info cpu field inside CONFIG_SMP #ifdefs moved to a separate patch.
>   - Removed CURRENT_THREAD_INFO macro completely.
>   - Added a guard in asm/smp.h to avoid build failure before _TASK_CPU is defined.
>   - Added a patch at the end to rename 'tp' pointers to 'sp' pointers
>   - Renamed 'tp' into 'sp' pointers in preparation patch when relevant
>   - Fixed a few commit logs
>   - Fixed checkpatch report.
> 
> Changes since RFC v2:
>   - Removed the modification of names in asm-offsets
>   - Created a rule in arch/powerpc/Makefile to append the offset of current->cpu in CFLAGS
>   - Modified asm/smp.h to use the offset set in CFLAGS
>   - Squashed the renaming of THREAD_INFO to TASK_STACK in the preparation patch
>   - Moved the modification of current_pt_regs in the patch activating CONFIG_THREAD_INFO_IN_TASK
> 
> Changes since RFC v1:
>   - Removed the first patch which was modifying header inclusion order in timer
>   - Modified some names in asm-offsets to avoid conflicts when including asm-offsets in C files
>   - Modified asm/smp.h to avoid having to include linux/sched.h (using asm-offsets instead)
>   - Moved some changes from the activation patch to the preparation patch.
> 
> Christophe Leroy (10):
>    powerpc/irq: use memblock functions returning virtual address
>    book3s/64: avoid circular header inclusion in mmu-hash.h
>    powerpc: Only use task_struct 'cpu' field on SMP
>    powerpc: Prepare for moving thread_info into task_struct
>    powerpc: Activate CONFIG_THREAD_INFO_IN_TASK
>    powerpc: regain entire stack space
>    powerpc: 'current_set' is now a table of task_struct pointers
>    powerpc/32: Remove CURRENT_THREAD_INFO and rename TI_CPU
>    powerpc/64: Remove CURRENT_THREAD_INFO
>    powerpc: clean stack pointers naming
> 
>   arch/powerpc/Kconfig                           |   1 +
>   arch/powerpc/Makefile                          |   7 ++
>   arch/powerpc/include/asm/asm-prototypes.h      |   4 +-
>   arch/powerpc/include/asm/book3s/64/mmu-hash.h  |   2 +-
>   arch/powerpc/include/asm/exception-64s.h       |   4 +-
>   arch/powerpc/include/asm/irq.h                 |  18 ++--
>   arch/powerpc/include/asm/livepatch.h           |   6 +-
>   arch/powerpc/include/asm/processor.h           |  39 +--------
>   arch/powerpc/include/asm/ptrace.h              |   2 +-
>   arch/powerpc/include/asm/reg.h                 |   2 +-
>   arch/powerpc/include/asm/smp.h                 |  17 +++-
>   arch/powerpc/include/asm/task_size_user64.h    |  42 +++++++++
>   arch/powerpc/include/asm/thread_info.h         |  19 -----
>   arch/powerpc/kernel/asm-offsets.c              |  10 ++-
>   arch/powerpc/kernel/entry_32.S                 |  66 +++++---------
>   arch/powerpc/kernel/entry_64.S                 |  12 +--
>   arch/powerpc/kernel/epapr_hcalls.S             |   5 +-
>   arch/powerpc/kernel/exceptions-64e.S           |  13 +--
>   arch/powerpc/kernel/exceptions-64s.S           |   2 +-
>   arch/powerpc/kernel/head_32.S                  |  14 +--
>   arch/powerpc/kernel/head_40x.S                 |   4 +-
>   arch/powerpc/kernel/head_44x.S                 |   8 +-
>   arch/powerpc/kernel/head_64.S                  |   1 +
>   arch/powerpc/kernel/head_8xx.S                 |   2 +-
>   arch/powerpc/kernel/head_booke.h               |  12 +--
>   arch/powerpc/kernel/head_fsl_booke.S           |  16 ++--
>   arch/powerpc/kernel/idle_6xx.S                 |   8 +-
>   arch/powerpc/kernel/idle_book3e.S              |   2 +-
>   arch/powerpc/kernel/idle_e500.S                |   8 +-
>   arch/powerpc/kernel/idle_power4.S              |   2 +-
>   arch/powerpc/kernel/irq.c                      | 114 +++----------------------
>   arch/powerpc/kernel/kgdb.c                     |  28 ------
>   arch/powerpc/kernel/machine_kexec_64.c         |   6 +-
>   arch/powerpc/kernel/misc_32.S                  |  17 ++--
>   arch/powerpc/kernel/process.c                  |  40 ++++-----
>   arch/powerpc/kernel/setup-common.c             |   2 +-
>   arch/powerpc/kernel/setup_32.c                 |  25 +++---
>   arch/powerpc/kernel/setup_64.c                 |  51 +++--------
>   arch/powerpc/kernel/smp.c                      |  16 ++--
>   arch/powerpc/kernel/trace/ftrace_64_mprofile.S |   6 +-
>   arch/powerpc/kvm/book3s_hv_hmi.c               |   1 +
>   arch/powerpc/mm/hash_low_32.S                  |  14 ++-
>   arch/powerpc/net/bpf_jit32.h                   |   5 +-
>   arch/powerpc/sysdev/6xx-suspend.S              |   5 +-
>   arch/powerpc/xmon/xmon.c                       |   2 +-
>   45 files changed, 249 insertions(+), 431 deletions(-)
>   create mode 100644 arch/powerpc/include/asm/task_size_user64.h
>