Re: [PATCH v6 net-next 4/9] vhost-net: allow configuring extended features

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Jun 27, 2025 at 12:28:00PM +0200, Paolo Abeni wrote:
> On 6/27/25 8:41 AM, kernel test robot wrote:
> > kernel test robot noticed the following build warnings:
> > 
> > [auto build test WARNING on net-next/main]
> > 
> > url:    https://github.com/intel-lab-lkp/linux/commits/Paolo-Abeni/scripts-kernel_doc-py-properly-handle-VIRTIO_DECLARE_FEATURES/20250624-221751
> > base:   net-next/main
> > patch link:    https://lore.kernel.org/r/23e46bff5333015d92bf0876033750d9fbf555a0.1750753211.git.pabeni%40redhat.com
> > patch subject: [PATCH v6 net-next 4/9] vhost-net: allow configuring extended features
> > config: csky-randconfig-001-20250627 (https://download.01.org/0day-ci/archive/20250627/202506271443.G9cAx8PS-lkp@intel.com/config)
> > compiler: csky-linux-gcc (GCC) 15.1.0
> > reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250627/202506271443.G9cAx8PS-lkp@intel.com/reproduce)
> > 
> > If you fix the issue in a separate patch/commit (i.e. not just a new version of
> > the same patch/commit), kindly add following tags
> > | Reported-by: kernel test robot <lkp@intel.com>
> > | Closes: https://lore.kernel.org/oe-kbuild-all/202506271443.G9cAx8PS-lkp@intel.com/
> > 
> > All warnings (new ones prefixed by >>):
> > 
> >    In file included from include/linux/uaccess.h:12,
> >                     from include/linux/sched/task.h:13,
> >                     from include/linux/sched/signal.h:9,
> >                     from include/linux/rcuwait.h:6,
> >                     from include/linux/percpu-rwsem.h:7,
> >                     from include/linux/fs.h:34,
> >                     from include/linux/compat.h:17,
> >                     from drivers/vhost/net.c:8:
> >    arch/csky/include/asm/uaccess.h: In function '__get_user_fn.constprop':
> >>> arch/csky/include/asm/uaccess.h:147:9: warning: 'retval' is used uninitialized [-Wuninitialized]
> >      147 |         __asm__ __volatile__(                           \
> >          |         ^~~~~~~
> >    arch/csky/include/asm/uaccess.h:187:17: note: in expansion of macro '__get_user_asm_64'
> >      187 |                 __get_user_asm_64(x, ptr, retval);
> >          |                 ^~~~~~~~~~~~~~~~~
> >    arch/csky/include/asm/uaccess.h:170:13: note: 'retval' was declared here
> >      170 |         int retval;
> >          |             ^~~~~~
> > 
> > 
> > vim +/retval +147 arch/csky/include/asm/uaccess.h
> > 
> > da551281947cb2c Guo Ren 2018-09-05  141  
> > e58a41c2226847f Guo Ren 2021-04-21  142  #define __get_user_asm_64(x, ptr, err)			\
> > da551281947cb2c Guo Ren 2018-09-05  143  do {							\
> > da551281947cb2c Guo Ren 2018-09-05  144  	int tmp;					\
> > e58a41c2226847f Guo Ren 2021-04-21  145  	int errcode;					\
> > e58a41c2226847f Guo Ren 2021-04-21  146  							\
> > e58a41c2226847f Guo Ren 2021-04-21 @147  	__asm__ __volatile__(				\
> > e58a41c2226847f Guo Ren 2021-04-21  148  	"1:   ldw     %3, (%2, 0)     \n"		\
> > da551281947cb2c Guo Ren 2018-09-05  149  	"     stw     %3, (%1, 0)     \n"		\
> > e58a41c2226847f Guo Ren 2021-04-21  150  	"2:   ldw     %3, (%2, 4)     \n"		\
> > e58a41c2226847f Guo Ren 2021-04-21  151  	"     stw     %3, (%1, 4)     \n"		\
> > e58a41c2226847f Guo Ren 2021-04-21  152  	"     br      4f              \n"		\
> > e58a41c2226847f Guo Ren 2021-04-21  153  	"3:   mov     %0, %4          \n"		\
> > e58a41c2226847f Guo Ren 2021-04-21  154  	"     br      4f              \n"		\
> > da551281947cb2c Guo Ren 2018-09-05  155  	".section __ex_table, \"a\"   \n"		\
> > da551281947cb2c Guo Ren 2018-09-05  156  	".align   2                   \n"		\
> > e58a41c2226847f Guo Ren 2021-04-21  157  	".long    1b, 3b              \n"		\
> > e58a41c2226847f Guo Ren 2021-04-21  158  	".long    2b, 3b              \n"		\
> > da551281947cb2c Guo Ren 2018-09-05  159  	".previous                    \n"		\
> > e58a41c2226847f Guo Ren 2021-04-21  160  	"4:                           \n"		\
> > e58a41c2226847f Guo Ren 2021-04-21  161  	: "=r"(err), "=r"(x), "=r"(ptr),		\
> > e58a41c2226847f Guo Ren 2021-04-21  162  	  "=r"(tmp), "=r"(errcode)			\
> > e58a41c2226847f Guo Ren 2021-04-21  163  	: "0"(err), "1"(x), "2"(ptr), "3"(0),		\
> > e58a41c2226847f Guo Ren 2021-04-21  164  	  "4"(-EFAULT)					\
> > da551281947cb2c Guo Ren 2018-09-05  165  	: "memory");					\
> > da551281947cb2c Guo Ren 2018-09-05  166  } while (0)
> > da551281947cb2c Guo Ren 2018-09-05  167  
> 
> AFAICS the issue reported here is in the arch-specific uaccess helpers
> and not related to this series.
> 
> /P

I think it's due to code like this in your patch:

+                       if (get_user(features, featurep + 1 + i))
+                               return -EFAULT;

the specific arch might have a bug that this is unconvering,
or a limitation, I can't say.

Seems worth fixing, though.

Poke the mainatiners?
-- 
MST