----- On Jul 8, 2018, at 5:03 PM, Mathieu Desnoyers mathieu.desnoy...@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': >> (.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 > > Signed-off-by: Mathieu Desnoyers <mathieu.desnoy...@efficios.com> > CC: Thomas Gleixner <t...@linutronix.de> > Cc: Joel Fernandes <joe...@google.com> > Cc: Peter Zijlstra <pet...@infradead.org> > Cc: Catalin Marinas <catalin.mari...@arm.com> > Cc: Dave Watson <davejwat...@fb.com> > Cc: Will Deacon <will.dea...@arm.com> > Cc: Andi Kleen <a...@firstfloor.org> > Cc: "H . Peter Anvin" <h...@zytor.com> > Cc: Chris Lameter <c...@linux.com> > Cc: Russell King <li...@arm.linux.org.uk> > Cc: Andrew Hunter <a...@google.com> > Cc: Michael Kerrisk <mtk.manpa...@gmail.com> > Cc: "Paul E . McKenney" <paul...@linux.vnet.ibm.com> > Cc: Paul Turner <p...@google.com> > Cc: Boqun Feng <boqun.f...@gmail.com> > Cc: Josh Triplett <j...@joshtriplett.org> > Cc: Steven Rostedt <rost...@goodmis.org> > Cc: Ben Maurer <bmau...@fb.com> > Cc: linux-...@vger.kernel.org > CC: linux-arm-ker...@lists.infradead.org > Cc: Andy Lutomirski <l...@amacapital.net> > Cc: Andrew Morton <a...@linux-foundation.org> > Cc: Linus Torvalds <torva...@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, struct > rseq_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, u32 > cs_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
