Re: [PATCH 1/1 v2] KVM: MMU: Optimize guest page table walk

[Avi Kivity <avi@redhat.com>]

On 04/26/2011 10:45 AM, Jan Kiszka wrote:
> On 2011-04-26 09:42, Avi Kivity wrote:
> >  On 04/25/2011 11:04 AM, Jan Kiszka wrote:
> >>  >   +
> >>  >   +        ptep_user = (pt_element_t __user *)((void *)host_addr +
> >>  offset);
> >>  >   +        if (get_user(pte, ptep_user)) {
> >>                       ^^^^^^^^^^^^
> >>  This doesn't work for x86-32: pte is 64 bit, but get_user is only
> >>  defined up to 32 bit on that platform.
> >>
> >
> >  I actually considered this, and saw:
> >
> >  #ifdef CONFIG_X86_32
> >  #define __get_user_8(__ret_gu, __val_gu, ptr)                \
> >          __get_user_x(X, __ret_gu, __val_gu, ptr)
> >  #else
> >  #define __get_user_8(__ret_gu, __val_gu, ptr)                \
> >          __get_user_x(8, __ret_gu, __val_gu, ptr)
> >  #endif
> >
> >  #define get_user(x, ptr)                        \
> >  ({                                    \
> >      int __ret_gu;                            \
> >      unsigned long __val_gu;                        \
> >      __chk_user_ptr(ptr);                        \
> >      might_fault();                            \
> >      switch (sizeof(*(ptr))) {                    \
> >
> >  ...
> >
> >      case 8:                                \
> >          __get_user_8(__ret_gu, __val_gu, ptr);            \
> >          break;                            \
> >
> >  ...
> >
> >      }                                \
> >      (x) = (__typeof__(*(ptr)))__val_gu;                \
> >      __ret_gu;                            \
> >  })
> >
> >  so it should work.  How does it fail?
>
> On x86-32, the above macro resolves to __get_user_X, an undefined symbol.
>

Tricky stuff.

-- 
error compiling committee.c: too many arguments to function