[PATCH] IB/mlx5: Fix binary compatibility with libmlx5

[PATCH] IB/mlx5: Fix binary compatibility with libmlx5

[Eli Cohen]

Commit c1be523 "Fix micro UAR allocator" broke binary compatibility between
libmlx5 and mlx5_ib since it defines a different value to the number of micro
UARs per page, leading to wrong calculation in libmlx5. This patch defines
struct mlx5_ib_alloc_ucontext_req_v2 as an extension to struct
mlx5_ib_alloc_ucontext_req.  The extended size is determined in
mlx5_ib_alloc_ucontext() and in case of old library we use uuarn 0 which works
fine. For new libraries we use the more sophisticated allocation algorithm.

Fixes: c1be523 ('Fix micro UAR allocator')
Signed-off-by: Eli Cohen <eli-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
---

Hi Roland, 

This fixes a regression introduced during the 3.14 merge window, and must
be applied for 3.14, thanks

Eli

 drivers/infiniband/hw/mlx5/main.c | 19 +++++++++++++++++--
 drivers/infiniband/hw/mlx5/qp.c   | 11 +++++++++--
 drivers/infiniband/hw/mlx5/user.h |  7 +++++++
 include/linux/mlx5/driver.h       |  1 +
 4 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/drivers/infiniband/hw/mlx5/main.c b/drivers/infiniband/hw/mlx5/main.c
index 9660d09..e24d912 100644
--- a/drivers/infiniband/hw/mlx5/main.c
+++ b/drivers/infiniband/hw/mlx5/main.c
@@ -536,24 +536,38 @@ static struct ib_ucontext *mlx5_ib_alloc_ucontext(struct ib_device *ibdev,
 						  struct ib_udata *udata)
 {
 	struct mlx5_ib_dev *dev = to_mdev(ibdev);
-	struct mlx5_ib_alloc_ucontext_req req;
+	struct mlx5_ib_alloc_ucontext_req_v2 req;
 	struct mlx5_ib_alloc_ucontext_resp resp;
 	struct mlx5_ib_ucontext *context;
 	struct mlx5_uuar_info *uuari;
 	struct mlx5_uar *uars;
 	int gross_uuars;
 	int num_uars;
+	int ver;
 	int uuarn;
 	int err;
 	int i;
+	int reqlen;
 
 	if (!dev->ib_active)
 		return ERR_PTR(-EAGAIN);
 
-	err = ib_copy_from_udata(&req, udata, sizeof(req));
+	memset(&req, 0, sizeof(req));
+	reqlen = udata->inlen - sizeof(struct ib_uverbs_get_context);
+	if (reqlen == sizeof(struct mlx5_ib_alloc_ucontext_req))
+		ver = 0;
+	else if (reqlen == sizeof(struct mlx5_ib_alloc_ucontext_req_v2))
+		ver = 2;
+	else
+		return ERR_PTR(-EINVAL);
+
+	err = ib_copy_from_udata(&req, udata, reqlen);
 	if (err)
 		return ERR_PTR(err);
 
+	if (req.flags || req.reserved)
+		return ERR_PTR(-EINVAL);
+
 	if (req.total_num_uuars > MLX5_MAX_UUARS)
 		return ERR_PTR(-ENOMEM);
 
@@ -626,6 +640,7 @@ static struct ib_ucontext *mlx5_ib_alloc_ucontext(struct ib_device *ibdev,
 	if (err)
 		goto out_uars;
 
+	uuari->ver = ver;
 	uuari->num_low_latency_uuars = req.num_low_latency_uuars;
 	uuari->uars = uars;
 	uuari->num_uars = num_uars;
diff --git a/drivers/infiniband/hw/mlx5/qp.c b/drivers/infiniband/hw/mlx5/qp.c
index 492dc33..300475c 100644
--- a/drivers/infiniband/hw/mlx5/qp.c
+++ b/drivers/infiniband/hw/mlx5/qp.c
@@ -430,11 +430,17 @@ static int alloc_uuar(struct mlx5_uuar_info *uuari,
 		break;
 
 	case MLX5_IB_LATENCY_CLASS_MEDIUM:
-		uuarn = alloc_med_class_uuar(uuari);
+		if (uuari->ver < 2)
+			uuarn = -ENOMEM;
+		else
+			uuarn = alloc_med_class_uuar(uuari);
 		break;
 
 	case MLX5_IB_LATENCY_CLASS_HIGH:
-		uuarn = alloc_high_class_uuar(uuari);
+		if (uuari->ver < 2)
+			uuarn = -ENOMEM;
+		else
+			uuarn = alloc_high_class_uuar(uuari);
 		break;
 
 	case MLX5_IB_LATENCY_CLASS_FAST_PATH:
@@ -559,6 +565,7 @@ static int create_user_qp(struct mlx5_ib_dev *dev, struct ib_pd *pd,
 		}
 	}
 
+
 	uar_index = uuarn_to_uar_index(&context->uuari, uuarn);
 	mlx5_ib_dbg(dev, "uuarn 0x%x, uar_index 0x%x\n", uuarn, uar_index);
 
diff --git a/drivers/infiniband/hw/mlx5/user.h b/drivers/infiniband/hw/mlx5/user.h
index 32a2a5d..0f4f8e4 100644
--- a/drivers/infiniband/hw/mlx5/user.h
+++ b/drivers/infiniband/hw/mlx5/user.h
@@ -62,6 +62,13 @@ struct mlx5_ib_alloc_ucontext_req {
 	__u32	num_low_latency_uuars;
 };
 
+struct mlx5_ib_alloc_ucontext_req_v2 {
+	__u32	total_num_uuars;
+	__u32	num_low_latency_uuars;
+	__u32	flags;
+	__u32	reserved;
+};
+
 struct mlx5_ib_alloc_ucontext_resp {
 	__u32	qp_tab_size;
 	__u32	bf_reg_size;
diff --git a/include/linux/mlx5/driver.h b/include/linux/mlx5/driver.h
index 554548c..32cb18c 100644
--- a/include/linux/mlx5/driver.h
+++ b/include/linux/mlx5/driver.h
@@ -227,6 +227,7 @@ struct mlx5_uuar_info {
 	 * protect uuar allocation data structs
 	 */
 	struct mutex		lock;
+	u32			ver;
 };
 
 struct mlx5_bf {
-- 
1.8.5.2

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Re: [PATCH] IB/mlx5: Fix binary compatibility with libmlx5

[Yann Droneaud]

Hi,

Le mercredi 29 janvier 2014 à 16:27 +0200, Eli Cohen a écrit :
> Commit c1be523 "Fix micro UAR allocator" broke binary compatibility between
        ^^^^^^^

12 digits identifier are the norm for kernel. Please update your git
configuration:

 git config --global core.abbrev 12

See http://lwn.net/Articles/571980/
    http://blog.cuviper.com/2013/11/10/how-short-can-git-abbreviate/

> libmlx5 and mlx5_ib since it defines a different value to the number of micro
> UARs per page, leading to wrong calculation in libmlx5. This patch defines
> struct mlx5_ib_alloc_ucontext_req_v2 as an extension to struct
> mlx5_ib_alloc_ucontext_req.  The extended size is determined in
> mlx5_ib_alloc_ucontext() and in case of old library we use uuarn 0 which works
> fine. For new libraries we use the more sophisticated allocation algorithm.
> 
> Fixes: c1be523 ('Fix micro UAR allocator')
        ^^^^^^^
Likewise

> Signed-off-by: Eli Cohen <eli-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>
> ---
> 
> Hi Roland, 
> 
> This fixes a regression introduced during the 3.14 merge window, and must
> be applied for 3.14, thanks
> 
> Eli
> 
>  drivers/infiniband/hw/mlx5/main.c | 19 +++++++++++++++++--
>  drivers/infiniband/hw/mlx5/qp.c   | 11 +++++++++--
>  drivers/infiniband/hw/mlx5/user.h |  7 +++++++
>  include/linux/mlx5/driver.h       |  1 +
>  4 files changed, 34 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/infiniband/hw/mlx5/main.c b/drivers/infiniband/hw/mlx5/main.c
> index 9660d09..e24d912 100644
> --- a/drivers/infiniband/hw/mlx5/main.c
> +++ b/drivers/infiniband/hw/mlx5/main.c
> @@ -536,24 +536,38 @@ static struct ib_ucontext *mlx5_ib_alloc_ucontext(struct ib_device *ibdev,
>  						  struct ib_udata *udata)
>  {
>  	struct mlx5_ib_dev *dev = to_mdev(ibdev);
> -	struct mlx5_ib_alloc_ucontext_req req;
> +	struct mlx5_ib_alloc_ucontext_req_v2 req;
>  	struct mlx5_ib_alloc_ucontext_resp resp;
>  	struct mlx5_ib_ucontext *context;
>  	struct mlx5_uuar_info *uuari;
>  	struct mlx5_uar *uars;
>  	int gross_uuars;
>  	int num_uars;
> +	int ver;
>  	int uuarn;
>  	int err;
>  	int i;
> +	int reqlen;
>  
>  	if (!dev->ib_active)
>  		return ERR_PTR(-EAGAIN);
>  
> -	err = ib_copy_from_udata(&req, udata, sizeof(req));
> +	memset(&req, 0, sizeof(req));
> +	reqlen = udata->inlen - sizeof(struct ib_uverbs_get_context);

I'm not sure how this could work without subtracting sizeof(struct
ib_uverbs_cmd_hdr).

As I explained in "Re: [PATCHv4 for-3.13 00/10] create_flow/destroy_flow
fixes for v3.13" [1] ib_uverbs_write() does not decrement input length:
it gives hdr.in_words * 4 to the uverbs function, here 
ib_uverbs_get_context(). Then, the function built struct ib_udata 
without taking care of the extra bytes count in in_len:

    struct ib_uverbs_get_context cmd;
    ...
    INIT_UDATA(&udata, buf + sizeof cmd,
               (unsigned long) cmd.response + sizeof resp,
               in_len - sizeof cmd, out_len - sizeof resp);

Driver mthca does some handling which look like to what's proposed in
your patch, but takes care of subtracting the header size from the input
length, see mthca_reg_user_mr()[2].

[1]
<http://marc.info/?i=1387493822.11925.217.camel-bi+AKbBUZKY6gyzm1THtWbp2dZbC/Bob@public.gmane.org>

[2]
<http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/infiniband/hw/mthca/mthca_provider.c?id=0e47c969c65e213421450c31043353ebe3c67e0c#n988>

> +	if (reqlen == sizeof(struct mlx5_ib_alloc_ucontext_req))
> +		ver = 0;
> +	else if (reqlen == sizeof(struct mlx5_ib_alloc_ucontext_req_v2))
> +		ver = 2;
> +	else
> +		return ERR_PTR(-EINVAL);
> +

Doing so introduce a subtle regression: there was no check on the length
before, so it was legal to pass a input buffer far larger than needed,
aka. trailing garbage. 

With such new test in place, it's no more allowed, and this is a
regression. It's not a big issue, but a little departure from current
behavor.

BTW, this is the correct way to handle the request, every other uverbs
functions should behave like this, eg. being strict on its accepted
input.

> +	err = ib_copy_from_udata(&req, udata, reqlen);
>  	if (err)
>  		return ERR_PTR(err);
>  
> +	if (req.flags || req.reserved)
> +		return ERR_PTR(-EINVAL);
> +

Just like this :)

>  	if (req.total_num_uuars > MLX5_MAX_UUARS)
>  		return ERR_PTR(-ENOMEM);
>  
> @@ -626,6 +640,7 @@ static struct ib_ucontext *mlx5_ib_alloc_ucontext(struct ib_device *ibdev,
>  	if (err)
>  		goto out_uars;
>  
> +	uuari->ver = ver;
>  	uuari->num_low_latency_uuars = req.num_low_latency_uuars;
>  	uuari->uars = uars;
>  	uuari->num_uars = num_uars;
> diff --git a/drivers/infiniband/hw/mlx5/qp.c b/drivers/infiniband/hw/mlx5/qp.c
> index 492dc33..300475c 100644
> --- a/drivers/infiniband/hw/mlx5/qp.c
> +++ b/drivers/infiniband/hw/mlx5/qp.c
> @@ -430,11 +430,17 @@ static int alloc_uuar(struct mlx5_uuar_info *uuari,
>  		break;
>  
>  	case MLX5_IB_LATENCY_CLASS_MEDIUM:
> -		uuarn = alloc_med_class_uuar(uuari);
> +		if (uuari->ver < 2)
> +			uuarn = -ENOMEM;

In the commit message, you specified that uuarn is set to 0 when v1 is
used. But here it's set to -ENOMEM.

> +		else
> +			uuarn = alloc_med_class_uuar(uuari);
>  		break;
>  
>  	case MLX5_IB_LATENCY_CLASS_HIGH:
> -		uuarn = alloc_high_class_uuar(uuari);
> +		if (uuari->ver < 2)
> +			uuarn = -ENOMEM;

Likewise.

> +		else
> +			uuarn = alloc_high_class_uuar(uuari);
>  		break;
>  
>  	case MLX5_IB_LATENCY_CLASS_FAST_PATH:
> @@ -559,6 +565,7 @@ static int create_user_qp(struct mlx5_ib_dev *dev, struct ib_pd *pd,
>  		}
>  	}
>  
> +

Remove this white space.

>  	uar_index = uuarn_to_uar_index(&context->uuari, uuarn);
>  	mlx5_ib_dbg(dev, "uuarn 0x%x, uar_index 0x%x\n", uuarn, uar_index);
>  
> diff --git a/drivers/infiniband/hw/mlx5/user.h b/drivers/infiniband/hw/mlx5/user.h
> index 32a2a5d..0f4f8e4 100644
> --- a/drivers/infiniband/hw/mlx5/user.h
> +++ b/drivers/infiniband/hw/mlx5/user.h
> @@ -62,6 +62,13 @@ struct mlx5_ib_alloc_ucontext_req {
>  	__u32	num_low_latency_uuars;
>  };
>  
> +struct mlx5_ib_alloc_ucontext_req_v2 {
> +	__u32	total_num_uuars;
> +	__u32	num_low_latency_uuars;
> +	__u32	flags;
> +	__u32	reserved;
> +};
> +

>  struct mlx5_ib_alloc_ucontext_resp {
>  	__u32	qp_tab_size;
>  	__u32	bf_reg_size;
> diff --git a/include/linux/mlx5/driver.h b/include/linux/mlx5/driver.h
> index 554548c..32cb18c 100644
> --- a/include/linux/mlx5/driver.h
> +++ b/include/linux/mlx5/driver.h
> @@ -227,6 +227,7 @@ struct mlx5_uuar_info {
>  	 * protect uuar allocation data structs
>  	 */
>  	struct mutex		lock;
> +	u32			ver;
>  };
>  
>  struct mlx5_bf {

Regards.

-- 
Yann Droneaud
OPTEYA


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Re: [PATCH] IB/mlx5: Fix binary compatibility with libmlx5

[Eli Cohen]

On Wed, Jan 29, 2014 at 09:48:43PM +0100, Yann Droneaud wrote:
Yann,
thanks for reviewing, your comments are helpful :-)

> 
> 12 digits identifier are the norm for kernel. Please update your git
> configuration:
> 
>  git config --global core.abbrev 12
> 
> See http://lwn.net/Articles/571980/
>     http://blog.cuviper.com/2013/11/10/how-short-can-git-abbreviate/
> 
> > libmlx5 and mlx5_ib since it defines a different value to the number of micro
> > UARs per page, leading to wrong calculation in libmlx5. This patch defines
> > struct mlx5_ib_alloc_ucontext_req_v2 as an extension to struct
> > mlx5_ib_alloc_ucontext_req.  The extended size is determined in
> > mlx5_ib_alloc_ucontext() and in case of old library we use uuarn 0 which works
> > fine. For new libraries we use the more sophisticated allocation algorithm.
> > 
> > Fixes: c1be523 ('Fix micro UAR allocator')
>         ^^^^^^^
> Likewise

Will fix.
> 
> I'm not sure how this could work without subtracting sizeof(struct
> ib_uverbs_cmd_hdr).

struct ib_uverbs_get_context happens to have the same size as struct
ib_uverbs_cmd_hdr so it passed all my sanity tests. Correct, will fix
that too.
> 
> As I explained in "Re: [PATCHv4 for-3.13 00/10] create_flow/destroy_flow
> fixes for v3.13" [1] ib_uverbs_write() does not decrement input length:
> it gives hdr.in_words * 4 to the uverbs function, here 
> ib_uverbs_get_context(). Then, the function built struct ib_udata 
> without taking care of the extra bytes count in in_len:
> 
>     struct ib_uverbs_get_context cmd;
>     ...
>     INIT_UDATA(&udata, buf + sizeof cmd,
>                (unsigned long) cmd.response + sizeof resp,
>                in_len - sizeof cmd, out_len - sizeof resp);

So this just seems broken and the fix is to do the subtraction here so
the hardware driver gets the correct size without needing to subtract
the extra bytes, like this:
        INIT_UDATA(&udata, buf + sizeof cmd,
                   (unsigned long) cmd.response + sizeof resp,
                   in_len - sizeof cmd - sizeof (struct ib_uverbs_cmd_hdr),
                   out_len - sizeof resp);

And the hardware driver gets the correct size for its struct.
> 
> Driver mthca does some handling which look like to what's proposed in
> your patch, but takes care of subtracting the header size from the input
> length, see mthca_reg_user_mr()[2].
> 
> [1]
> <http://marc.info/?i=1387493822.11925.217.camel-bi+AKbBUZKY6gyzm1THtWbp2dZbC/Bob@public.gmane.org>
> 
> [2]
> <http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/infiniband/hw/mthca/mthca_provider.c?id=0e47c969c65e213421450c31043353ebe3c67e0c#n988>
> 
> > +	if (reqlen == sizeof(struct mlx5_ib_alloc_ucontext_req))
> > +		ver = 0;
> > +	else if (reqlen == sizeof(struct mlx5_ib_alloc_ucontext_req_v2))
> > +		ver = 2;
> > +	else
> > +		return ERR_PTR(-EINVAL);
> > +
> 
> Doing so introduce a subtle regression: there was no check on the length
> before, so it was legal to pass a input buffer far larger than needed,
> aka. trailing garbage. 
> 
> With such new test in place, it's no more allowed, and this is a
> regression. It's not a big issue, but a little departure from current
> behavor.
Well it's a regression if there was out there another library for mlx5
out there which misbehaves and there is any as far as I know. So I
think it's safe to add this strict check.
> 
> BTW, this is the correct way to handle the request, every other uverbs
> functions should behave like this, eg. being strict on its accepted
> input.
> 
> > +	err = ib_copy_from_udata(&req, udata, reqlen);
> >  	if (err)
> >  		return ERR_PTR(err);
> >  
> > +	if (req.flags || req.reserved)
> > +		return ERR_PTR(-EINVAL);
> > +
> 
> Just like this :)
> 
> >  	if (req.total_num_uuars > MLX5_MAX_UUARS)
> >  		return ERR_PTR(-ENOMEM);
> >  
> > @@ -626,6 +640,7 @@ static struct ib_ucontext *mlx5_ib_alloc_ucontext(struct ib_device *ibdev,
> >  	if (err)
> >  		goto out_uars;
> >  
> > +	uuari->ver = ver;
> >  	uuari->num_low_latency_uuars = req.num_low_latency_uuars;
> >  	uuari->uars = uars;
> >  	uuari->num_uars = num_uars;
> > diff --git a/drivers/infiniband/hw/mlx5/qp.c b/drivers/infiniband/hw/mlx5/qp.c
> > index 492dc33..300475c 100644
> > --- a/drivers/infiniband/hw/mlx5/qp.c
> > +++ b/drivers/infiniband/hw/mlx5/qp.c
> > @@ -430,11 +430,17 @@ static int alloc_uuar(struct mlx5_uuar_info *uuari,
> >  		break;
> >  
> >  	case MLX5_IB_LATENCY_CLASS_MEDIUM:
> > -		uuarn = alloc_med_class_uuar(uuari);
> > +		if (uuari->ver < 2)
> > +			uuarn = -ENOMEM;
> 
> In the commit message, you specified that uuarn is set to 0 when v1 is
> used. But here it's set to -ENOMEM.
> 
If you look at qp.c you can see that the code falls back from high to
medium to low class. Low class always succeeds and gives 0.

> > +		else
> > +			uuarn = alloc_med_class_uuar(uuari);
> >  		break;
> >  
> >  	case MLX5_IB_LATENCY_CLASS_HIGH:
> > -		uuarn = alloc_high_class_uuar(uuari);
> > +		if (uuari->ver < 2)
> > +			uuarn = -ENOMEM;
> 
> Likewise.
> 
> > +		else
> > +			uuarn = alloc_high_class_uuar(uuari);
> >  		break;
> >  
> >  	case MLX5_IB_LATENCY_CLASS_FAST_PATH:
> > @@ -559,6 +565,7 @@ static int create_user_qp(struct mlx5_ib_dev *dev, struct ib_pd *pd,
> >  		}
> >  	}
> >  
> > +
> 
> Remove this white space.
> 
> >  	uar_index = uuarn_to_uar_index(&context->uuari, uuarn);
> >  	mlx5_ib_dbg(dev, "uuarn 0x%x, uar_index 0x%x\n", uuarn, uar_index);
> >  
> > diff --git a/drivers/infiniband/hw/mlx5/user.h b/drivers/infiniband/hw/mlx5/user.h
> > index 32a2a5d..0f4f8e4 100644
> > --- a/drivers/infiniband/hw/mlx5/user.h
> > +++ b/drivers/infiniband/hw/mlx5/user.h
> > @@ -62,6 +62,13 @@ struct mlx5_ib_alloc_ucontext_req {
> >  	__u32	num_low_latency_uuars;
> >  };
> >  
> > +struct mlx5_ib_alloc_ucontext_req_v2 {
> > +	__u32	total_num_uuars;
> > +	__u32	num_low_latency_uuars;
> > +	__u32	flags;
> > +	__u32	reserved;
> > +};
> > +
> 
> >  struct mlx5_ib_alloc_ucontext_resp {
> >  	__u32	qp_tab_size;
> >  	__u32	bf_reg_size;
> > diff --git a/include/linux/mlx5/driver.h b/include/linux/mlx5/driver.h
> > index 554548c..32cb18c 100644
> > --- a/include/linux/mlx5/driver.h
> > +++ b/include/linux/mlx5/driver.h
> > @@ -227,6 +227,7 @@ struct mlx5_uuar_info {
> >  	 * protect uuar allocation data structs
> >  	 */
> >  	struct mutex		lock;
> > +	u32			ver;
> >  };
> >  
> >  struct mlx5_bf {
> 
> Regards.
> 
> -- 
> Yann Droneaud
> OPTEYA
> 
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Re: [PATCH] IB/mlx5: Fix binary compatibility with libmlx5

[Yann Droneaud]

Hi,

Le jeudi 30 janvier 2014 à 01:33 +0200, Eli Cohen a écrit :
> On Wed, Jan 29, 2014 at 09:48:43PM +0100, Yann Droneaud wrote:
> Yann,
> thanks for reviewing, your comments are helpful :-)
> 
> > 
> > 12 digits identifier are the norm for kernel. Please update your git
> > configuration:
> > 
> >  git config --global core.abbrev 12
> > 
> > See http://lwn.net/Articles/571980/
> >     http://blog.cuviper.com/2013/11/10/how-short-can-git-abbreviate/
> > 
> > > libmlx5 and mlx5_ib since it defines a different value to the number of micro
> > > UARs per page, leading to wrong calculation in libmlx5. This patch defines
> > > struct mlx5_ib_alloc_ucontext_req_v2 as an extension to struct
> > > mlx5_ib_alloc_ucontext_req.  The extended size is determined in
> > > mlx5_ib_alloc_ucontext() and in case of old library we use uuarn 0 which works
> > > fine. For new libraries we use the more sophisticated allocation algorithm.
> > > 
> > > Fixes: c1be523 ('Fix micro UAR allocator')
> >         ^^^^^^^
> > Likewise
> 
> Will fix.
> > 
> > I'm not sure how this could work without subtracting sizeof(struct
> > ib_uverbs_cmd_hdr).
> 
> struct ib_uverbs_get_context happens to have the same size as struct
> ib_uverbs_cmd_hdr so it passed all my sanity tests. Correct, will fix
> that too.
> > 
> > As I explained in "Re: [PATCHv4 for-3.13 00/10] create_flow/destroy_flow
> > fixes for v3.13" [1] ib_uverbs_write() does not decrement input length:
> > it gives hdr.in_words * 4 to the uverbs function, here 
> > ib_uverbs_get_context(). Then, the function built struct ib_udata 
> > without taking care of the extra bytes count in in_len:
> > 
> >     struct ib_uverbs_get_context cmd;
> >     ...
> >     INIT_UDATA(&udata, buf + sizeof cmd,
> >                (unsigned long) cmd.response + sizeof resp,
> >                in_len - sizeof cmd, out_len - sizeof resp);
> 
> So this just seems broken and the fix is to do the subtraction here so
> the hardware driver gets the correct size without needing to subtract
> the extra bytes, like this:

>         INIT_UDATA(&udata, buf + sizeof cmd,
>                    (unsigned long) cmd.response + sizeof resp,
>                    in_len - sizeof cmd - sizeof (struct ib_uverbs_cmd_hdr),
>                    out_len - sizeof resp);
> 

> And the hardware driver gets the correct size for its struct.
> 

It's not the place to address the issue: the proper fix is to subtract
it in ib_uverbs_write().
I have a patch for this but I'm not going to submit it for 3.14: it's
part of a patchset that need testing and polishing. I will submit this
large patchset for 3.15 (after v3.14-rc1).

So you have to subtract the header size in your driver, just like mthca
does. And don't worry I will take care of removing it in my patch that
remove the header size from input length.

> > 
> > Driver mthca does some handling which look like to what's proposed in
> > your patch, but takes care of subtracting the header size from the input
> > length, see mthca_reg_user_mr()[2].
> > 
> > [1]
> > <http://marc.info/?i=1387493822.11925.217.camel-bi+AKbBUZKY6gyzm1THtWWGXanvQGlWp@public.gmane.orgmain>
> > 
> > [2]
> > <http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/infiniband/hw/mthca/mthca_provider.c?id=0e47c969c65e213421450c31043353ebe3c67e0c#n988>
> > 
> > > +	if (reqlen == sizeof(struct mlx5_ib_alloc_ucontext_req))
> > > +		ver = 0;
> > > +	else if (reqlen == sizeof(struct mlx5_ib_alloc_ucontext_req_v2))
> > > +		ver = 2;
> > > +	else
> > > +		return ERR_PTR(-EINVAL);
> > > +
> > 
> > Doing so introduce a subtle regression: there was no check on the length
> > before, so it was legal to pass a input buffer far larger than needed,
> > aka. trailing garbage. 
> > 
> > With such new test in place, it's no more allowed, and this is a
> > regression. It's not a big issue, but a little departure from current
> > behavor.

> Well it's a regression if there was out there another library for mlx5
> out there which misbehaves and there is any as far as I know. So I
> think it's safe to add this strict check.

Yes I think so.

But as I'm used to write it here, there's no clear line drawn: where is
the ABI that we should enforce ? Is it the kernel uverbs data structure
for response and request or libuverbs/lib<hw> ? In the first case, your
change add a regression, in the second case, it's not. It's just a
theoretical question. In practice, as you wrote, we can say there's no
other library that implement the userspace part of mlx5 rdma driver.

> > 
> > BTW, this is the correct way to handle the request, every other uverbs
> > functions should behave like this, eg. being strict on its accepted
> > input.
> > 
> > > +	err = ib_copy_from_udata(&req, udata, reqlen);
> > >  	if (err)
> > >  		return ERR_PTR(err);
> > >  
> > > +	if (req.flags || req.reserved)
> > > +		return ERR_PTR(-EINVAL);
> > > +
> > 
> > Just like this :)
> > 
> > >  	if (req.total_num_uuars > MLX5_MAX_UUARS)
> > >  		return ERR_PTR(-ENOMEM);
> > >  
> > > @@ -626,6 +640,7 @@ static struct ib_ucontext *mlx5_ib_alloc_ucontext(struct ib_device *ibdev,
> > >  	if (err)
> > >  		goto out_uars;
> > >  
> > > +	uuari->ver = ver;
> > >  	uuari->num_low_latency_uuars = req.num_low_latency_uuars;
> > >  	uuari->uars = uars;
> > >  	uuari->num_uars = num_uars;
> > > diff --git a/drivers/infiniband/hw/mlx5/qp.c b/drivers/infiniband/hw/mlx5/qp.c
> > > index 492dc33..300475c 100644
> > > --- a/drivers/infiniband/hw/mlx5/qp.c
> > > +++ b/drivers/infiniband/hw/mlx5/qp.c
> > > @@ -430,11 +430,17 @@ static int alloc_uuar(struct mlx5_uuar_info *uuari,
> > >  		break;
> > >  
> > >  	case MLX5_IB_LATENCY_CLASS_MEDIUM:
> > > -		uuarn = alloc_med_class_uuar(uuari);
> > > +		if (uuari->ver < 2)
> > > +			uuarn = -ENOMEM;
> > 
> > In the commit message, you specified that uuarn is set to 0 when v1 is
> > used. But here it's set to -ENOMEM.
> > 
> If you look at qp.c you can see that the code falls back from high to
> medium to low class. Low class always succeeds and gives 0.
> 

It was not clear from the commit message.

> > > +		else
> > > +			uuarn = alloc_med_class_uuar(uuari);
> > >  		break;
> > >  
> > >  	case MLX5_IB_LATENCY_CLASS_HIGH:
> > > -		uuarn = alloc_high_class_uuar(uuari);
> > > +		if (uuari->ver < 2)
> > > +			uuarn = -ENOMEM;
> > 
> > Likewise.
> > 
> > > +		else
> > > +			uuarn = alloc_high_class_uuar(uuari);
> > >  		break;
> > >  

Regards

-- 
Yann Droneaud
OPTEYA


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