RE: [PATCH] sample/hw_breakpoint: avoid sample hw_breakpoint recursion for arm/arm64
-Original Message- From: Peter Zijlstra [mailto:pet...@infradead.org] Sent: Thursday, September 26, 2019 5:14 PM To: wangxu (AE) Cc: mi...@redhat.com; a...@kernel.org; mark.rutl...@arm.com; alexander.shish...@linux.intel.com; namhy...@kernel.org; gre...@linuxfoundation.org; t...@linutronix.de; rfont...@redhat.com; alli...@lohutok.net; linux-kernel@vger.kernel.org Subject: Re: [PATCH] sample/hw_breakpoint: avoid sample hw_breakpoint recursion for arm/arm64 On Mon, Sep 23, 2019 at 04:09:35PM +0800, wangxu wrote: > From: Wang Xu > > For x86/ppc, hw_breakpoint is triggered after the instruction is > executed. > > For arm/arm64, which is triggered before the instruction executed. > Arm/arm64 skips the instruction by using single step. But it only > supports default overflow_handler. Where is the recusion.. ? For arm/arm64, hw_breakpoint is triggered before the instruction executed. When instruction_A is triggered, watchpoint_handler() will deal with this exception, and after return instruction_A will be triggerd ... One using samples/hw_breakpoint/data_breakpoint.c in arm/arm64 will meet this problem. > This patch provides a chance to avoid sample hw_breakpoint recursion > for arm/arm64 by adding 'struct perf_event_attr.bp_step'. This patch also lacks justification for why this needs to come with ABI changes. There is also a distinct lack of comments. I agree too. but have no better idea... This problem is really a big pit, especially for one not familiar with implementation differences in hw breakpoint for different architectures. > Signed-off-by: Wang Xu > --- > include/linux/perf_event.h | 3 +++ > include/uapi/linux/perf_event.h | 3 ++- > samples/hw_breakpoint/data_breakpoint.c | 1 + > 3 files changed, 6 insertions(+), 1 deletion(-) > > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h > index 61448c1..f270eb7 100644 > --- a/include/linux/perf_event.h > +++ b/include/linux/perf_event.h > @@ -1024,6 +1024,9 @@ extern int perf_event_output(struct perf_event *event, > return true; > if (unlikely(event->overflow_handler == perf_event_output_backward)) > return true; > + /* avoid sample hw_breakpoint recursion */ > + if (unlikely(event->attr.bp_step)) > + return true; This is just _wrong_.. it says that every event with bp_step set always is a 'default overflow handler', irrespective of what the overflow handler actually is. Thanks for comments. Function is_default_overflow_handler() was introduced in 1879445dfa7bbd6fe21b09c5cc72f4934798afed , which is only be called in arch/arm[64]/kernel/hw_breakpoint.c, and will never be used in other arch/ (I think). But keeping is_default_overflow_handler() unchanged, changing ' if (is_default_overflow_handler(bp)) ' to ' if (is_default_overflow_handler(bp) || unlikely(event->attr.bp_step) ) ' will be better in arch/arm[64]/kernel/hw_breakpoint.c. > return false; > } >
RE: [PATCH] vhost: It's better to use size_t for the 3rd parameter of vhost_exceeds_weight()
Hi Michael
Thanks for your fast reply.
As the following code, the 2nd branch of iov_iter_advance() does not
check if i->count < size, when this happens, i->count -= size may cause len
exceed INT_MAX, and then total_len exceed INT_MAX.
handle_tx_copy() ->
get_tx_bufs(..., , ...) ->
init_iov_iter() ->
iov_iter_advance(iter, ...) // has 3
branches:
pipe_advance() // has checked
the size: if (unlikely(i->count < size)) size = i->count;
iov_iter_is_discard() ... // no
check.
iterate_and_advance() //has checked:
if (unlikely(i->count < n)) n = i->count;
return iov_iter_count(iter);
-Original Message-
From: Michael S. Tsirkin [mailto:m...@redhat.com]
Sent: Monday, September 23, 2019 4:07 PM
To: wangxu (AE)
Cc: jasow...@redhat.com; k...@vger.kernel.org;
virtualizat...@lists.linux-foundation.org; net...@vger.kernel.org;
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] vhost: It's better to use size_t for the 3rd parameter of
vhost_exceeds_weight()
On Mon, Sep 23, 2019 at 03:46:41PM +0800, wangxu wrote:
> From: Wang Xu
>
> Caller of vhost_exceeds_weight(..., total_len) in drivers/vhost/net.c
> usually pass size_t total_len, which may be affected by rx/tx package.
>
> Signed-off-by: Wang Xu
Puts a bit more pressure on the register file ...
why do we care? Is there some way that it can exceed INT_MAX?
> ---
> drivers/vhost/vhost.c | 4 ++--
> drivers/vhost/vhost.h | 7 ---
> 2 files changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index
> 36ca2cf..159223a 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -412,7 +412,7 @@ static void vhost_dev_free_iovecs(struct vhost_dev
> *dev) }
>
> bool vhost_exceeds_weight(struct vhost_virtqueue *vq,
> - int pkts, int total_len)
> + int pkts, size_t total_len)
> {
> struct vhost_dev *dev = vq->dev;
>
> @@ -454,7 +454,7 @@ static size_t vhost_get_desc_size(struct
> vhost_virtqueue *vq,
>
> void vhost_dev_init(struct vhost_dev *dev,
> struct vhost_virtqueue **vqs, int nvqs,
> - int iov_limit, int weight, int byte_weight)
> + int iov_limit, int weight, size_t byte_weight)
> {
> struct vhost_virtqueue *vq;
> int i;
> diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h index
> e9ed272..8d80389d 100644
> --- a/drivers/vhost/vhost.h
> +++ b/drivers/vhost/vhost.h
> @@ -172,12 +172,13 @@ struct vhost_dev {
> wait_queue_head_t wait;
> int iov_limit;
> int weight;
> - int byte_weight;
> + size_t byte_weight;
> };
>
This just costs extra memory, and value is never large, so I don't think this
matters.
> -bool vhost_exceeds_weight(struct vhost_virtqueue *vq, int pkts, int
> total_len);
> +bool vhost_exceeds_weight(struct vhost_virtqueue *vq, int pkts,
> + size_t total_len);
> void vhost_dev_init(struct vhost_dev *, struct vhost_virtqueue **vqs,
> - int nvqs, int iov_limit, int weight, int byte_weight);
> + int nvqs, int iov_limit, int weight, size_t byte_weight);
> long vhost_dev_set_owner(struct vhost_dev *dev); bool
> vhost_dev_has_owner(struct vhost_dev *dev); long
> vhost_dev_check_owner(struct vhost_dev *);
> --
> 1.8.5.6
