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

[Avi Kivity <avi@redhat.com>]

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?

> Avi, what's your 32-bit buildbot doing? :)

I regularly autotest on x86_64, not on i386, sorry.

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