Re: [PATCH for 4.18 2/6] rseq: use get_user/put_user rather than __get_user/__put_user
From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: 2018-07-09 17:28:55
Also in:
linux-arm-kernel, lkml
----- On Jul 8, 2018, at 5:03 PM, Mathieu Desnoyers mathieu.desnoyers@efficios.com wrote:
In preparation to use __u64 for the rseq_cs pointer field, 32-bit architectures need to read this 64-bit value located in user-space addresses. __get_user is used to read this value, given that its access check has already been performed with access_ok() on rseq registration. arm does not implement 8-byte __get_user. Rather than trying to improve __get_user on ARM, use get_user/put_user across rseq instead. If those end up showing up in benchmarks, the proper approach would be to use user_access_begin() / unsafe_get/put_user() / user_access_end() anyway.
So, another twist to this story: ppc32 does not implement u64 get_user(). I am tempted to ditch this patch (leaving the __get_user()/__put_user as is for 32-bit accesses), and simply use __copy_from_user()/__copy_to_user() to load/store the rseq_cs pointer. Considering that we don't need to load/store the rseq_cs field with single-copy atomicity from the kernel anymore, it should be fine. Any objection ? tree: https://git.kernel.org/pub/scm/linux/kernel/git/rseq/linux-rseq.git rseq/dev head: a100323919af0c11a150a9ba58c3f8ac986ea42d commit: 23d0f99d280fa97ebcf8b915157468f457bc6e11 [4/21] rseq: uapi: declare rseq_cs field as union, update includes config: powerpc-ppc6xx_defconfig (attached as .config) compiler: powerpc-linux-gnu-gcc (Debian 7.2.0-11) 7.2.0 reproduce: wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross chmod +x ~/bin/make.cross git checkout 23d0f99d280fa97ebcf8b915157468f457bc6e11 # save the attached .config to linux build tree GCC_VERSION=7.2.0 make.cross ARCH=powerpc All errors (new ones prefixed by >>): kernel/rseq.o: In function `__rseq_handle_notify_resume':
quoted
(.text+0x648): undefined reference to `__get_user_bad'
--- 0-DAY kernel test infrastructure Open Source Technology Center https://lists.01.org/pipermail/kbuild-all Intel Corporation Thanks, Mathieu
quoted hunk ↗ jump to hunk
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> CC: Thomas Gleixner <redacted> Cc: Joel Fernandes <redacted> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Dave Watson <redacted> Cc: Will Deacon <redacted> Cc: Andi Kleen <redacted> Cc: "H . Peter Anvin" <hpa@zytor.com> Cc: Chris Lameter <redacted> Cc: Russell King <redacted> Cc: Andrew Hunter <redacted> Cc: Michael Kerrisk <redacted> Cc: "Paul E . McKenney" <redacted> Cc: Paul Turner <redacted> Cc: Boqun Feng <redacted> Cc: Josh Triplett <josh@joshtriplett.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Ben Maurer <redacted> Cc: linux-api@vger.kernel.org CC: linux-arm-kernel@lists.infradead.org Cc: Andy Lutomirski <luto@amacapital.net> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> --- kernel/rseq.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-)diff --git a/kernel/rseq.c b/kernel/rseq.c index 16b38c5342f9..2c8463acb50d 100644 --- a/kernel/rseq.c +++ b/kernel/rseq.c@@ -85,9 +85,9 @@ static int rseq_update_cpu_id(struct task_struct *t){ u32 cpu_id = raw_smp_processor_id(); - if (__put_user(cpu_id, &t->rseq->cpu_id_start)) + if (put_user(cpu_id, &t->rseq->cpu_id_start)) return -EFAULT; - if (__put_user(cpu_id, &t->rseq->cpu_id)) + if (put_user(cpu_id, &t->rseq->cpu_id)) return -EFAULT; trace_rseq_update(t); return 0;@@ -100,14 +100,14 @@ static int rseq_reset_rseq_cpu_id(struct task_struct *t)/* * Reset cpu_id_start to its initial state (0). */ - if (__put_user(cpu_id_start, &t->rseq->cpu_id_start)) + if (put_user(cpu_id_start, &t->rseq->cpu_id_start)) return -EFAULT; /* * Reset cpu_id to RSEQ_CPU_ID_UNINITIALIZED, so any user coming * in after unregistration can figure out that rseq needs to be * registered again. */ - if (__put_user(cpu_id, &t->rseq->cpu_id)) + if (put_user(cpu_id, &t->rseq->cpu_id)) return -EFAULT; return 0; }@@ -120,7 +120,7 @@ static int rseq_get_rseq_cs(struct task_struct *t, structrseq_cs *rseq_cs) u32 sig; int ret; - ret = __get_user(ptr, &t->rseq->rseq_cs); + ret = get_user(ptr, &t->rseq->rseq_cs); if (ret) return ret; if (!ptr) {@@ -163,7 +163,7 @@ static int rseq_need_restart(struct task_struct *t, u32cs_flags) int ret; /* Get thread flags. */ - ret = __get_user(flags, &t->rseq->flags); + ret = get_user(flags, &t->rseq->flags); if (ret) return ret;@@ -203,7 +203,7 @@ static int clear_rseq_cs(struct task_struct *t)* * Set rseq_cs to NULL with single-copy atomicity. */ - return __put_user(0UL, &t->rseq->rseq_cs); + return put_user(0UL, &t->rseq->rseq_cs); } /* -- 2.11.0
-- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com