Re: [PATCH v3 3/7] x86/xen: drop tests for highmem in pv code

[kernel test robot <lkp@xxxxxxxxx>]

Hi Juergen,

I love your patch! Perhaps something to improve:

[auto build test WARNING on tip/x86/core]
[also build test WARNING on tip/x86/asm v5.8 next-20200806]
[cannot apply to xen-tip/linux-next tip/x86/vdso]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    
https://github.com/0day-ci/linux/commits/Juergen-Gross/Remove-32-bit-Xen-PV-guest-support/20200807-164058
base:   https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git 
ef2ff0f5d6008d325c9a068e20981c0d0acc4d6b
config: x86_64-allyesconfig (attached as .config)
compiler: gcc-9 (Debian 9.3.0-15) 9.3.0
reproduce (this is a W=1 build):
        # save the attached .config to linux build tree
        make W=1 ARCH=x86_64 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@xxxxxxxxx>

All warnings (new ones prefixed by >>):

   arch/x86/xen/enlighten_pv.c: In function 'set_aliased_prot':
>> arch/x86/xen/enlighten_pv.c:348:15: warning: variable 'page' set but not 
>> used [-Wunused-but-set-variable]
     348 |  struct page *page;
         |               ^~~~
   arch/x86/xen/enlighten_pv.c: At top level:
   arch/x86/xen/enlighten_pv.c:1198:34: warning: no previous prototype for 
'xen_start_kernel' [-Wmissing-prototypes]
    1198 | asmlinkage __visible void __init xen_start_kernel(void)
         |                                  ^~~~~~~~~~~~~~~~

vim +/page +348 arch/x86/xen/enlighten_pv.c

e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  335  
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  336  /*
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  337   * Set the page permissions 
for a particular virtual address.  If the
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  338   * address is a vmalloc 
mapping (or other non-linear mapping), then
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  339   * find the linear mapping 
of the page and also set its protections to
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  340   * match.
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  341   */
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  342  static void 
set_aliased_prot(void *v, pgprot_t prot)
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  343  {
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  344       int level;
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  345       pte_t *ptep;
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  346       pte_t pte;
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  347       unsigned long pfn;
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14 @348       struct page *page;
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  349       unsigned char dummy;
64aef3716eab524 Juergen Gross     2020-08-07  350       void *av;
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  351  
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  352       ptep = 
lookup_address((unsigned long)v, &level);
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  353       BUG_ON(ptep == NULL);
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  354  
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  355       pfn = pte_pfn(*ptep);
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  356       page = pfn_to_page(pfn);
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  357  
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  358       pte = pfn_pte(pfn, 
prot);
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  359  
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  360       /*
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  361        * Careful: 
update_va_mapping() will fail if the virtual address
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  362        * we're poking isn't 
populated in the page tables.  We don't
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  363        * need to worry about 
the direct map (that's always in the page
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  364        * tables), but we need 
to be careful about vmap space.  In
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  365        * particular, the top 
level page table can lazily propagate
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  366        * entries between 
processes, so if we've switched mms since we
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  367        * vmapped the target 
in the first place, we might not have the
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  368        * top-level page table 
entry populated.
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  369        *
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  370        * We disable 
preemption because we want the same mm active when
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  371        * we probe the target 
and when we issue the hypercall.  We'll
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  372        * have the same 
nominal mm, but if we're a kernel thread, lazy
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  373        * mm dropping could 
change our pgd.
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  374        *
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  375        * Out of an abundance 
of caution, this uses __get_user() to fault
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  376        * in the target 
address just in case there's some obscure case
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  377        * in which the target 
address isn't readable.
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  378        */
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  379  
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  380       preempt_disable();
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  381  
fe557319aa06c23 Christoph Hellwig 2020-06-17  382       
copy_from_kernel_nofault(&dummy, v, 1);
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  383  
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  384       if 
(HYPERVISOR_update_va_mapping((unsigned long)v, pte, 0))
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  385               BUG();
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  386  
64aef3716eab524 Juergen Gross     2020-08-07  387       av = 
__va(PFN_PHYS(pfn));
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  388  
64aef3716eab524 Juergen Gross     2020-08-07  389       if (av != v && 
HYPERVISOR_update_va_mapping((unsigned long)av, pte, 0))
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  390               BUG();
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  391  
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  392       preempt_enable();
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  393  }
e1dab14cf68d1e0 Vitaly Kuznetsov  2017-03-14  394  

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