[Xen-devel] Re: [PATCH 2 of 7] x86/pvops: add a paravirt_ident functions to allow special patching

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

Rusty Russell wrote:
> On Thursday 29 January 2009 09:05:02 Jeremy Fitzhardinge wrote:
>   
> >  void _paravirt_nop(void);
> > +u32 _paravirt_ident_32(u32);
> > +u64 _paravirt_ident_64(u64);
> > +
> >  #define paravirt_nop   ((void *)_paravirt_nop)
> >     
> So, we used a void * cast for the paravirt_nop case, but you decided to use 
> explicit types for the ident cases?
>   
Yes.  Partly because any nop function is going to be basically 
equivalent to (void (*)(void)), but the concrete types for the ident 
function will vary (pointer, scalar, structure, etc).
> >         if (opfunc == NULL)
> >                 /* If there's no function, patch it with a ud2a (BUG) */
> >                 ret = paravirt_patch_insns(insnbuf, len, ud2a, 
> > ud2a+sizeof(ud2a));
> > -       else if (opfunc == paravirt_nop)
> > +       else if (opfunc == _paravirt_nop)
> >                 /* If the operation is a nop, then nop the callsite */
> >                 ret = paravirt_patch_nop();
> >     
> Gratuitous change?
>   
To make it consistent with the newly added lines following.  And its 
slightly more correct.
>   
> > +typedef pte_t make_pte_t(pteval_t);
> > +typedef pmd_t make_pmd_t(pmdval_t);
> > +typedef pud_t make_pud_t(pudval_t);
> > +typedef pgd_t make_pgd_t(pgdval_t);
> > +
> > +typedef pteval_t pte_val_t(pte_t);
> > +typedef pmdval_t pmd_val_t(pmd_t);
> > +typedef pudval_t pud_val_t(pud_t);
> > +typedef pgdval_t pgd_val_t(pgd_t);
> > +
> > +
> > +#if defined(CONFIG_X86_32) && !defined(CONFIG_X86_PAE)
> > +/* 32-bit pagetable entries */
> > +#define paravirt_native_make_pte       (make_pte_t *)_paravirt_ident_32
> > +#define paravirt_native_pte_val                (pte_val_t *)_paravirt_ident_32
> > +
> > +#define paravirt_native_make_pmd       (make_pmd_t *)_paravirt_ident_32
> > +#define paravirt_native_pmd_val                (pmd_val_t *)_paravirt_ident_32
> > +
> > +#define paravirt_native_make_pud       (make_pud_t *)_paravirt_ident_32
> > +#define paravirt_native_pud_val                (pud_val_t *)_paravirt_ident_32
> > +
> > +#define paravirt_native_make_pgd       (make_pgd_t *)_paravirt_ident_32
> > +#define paravirt_native_pgd_val                (pgd_val_t *)_paravirt_ident_32
> > +#else
> > +/* 64-bit pagetable entries */
> > +#define paravirt_native_make_pte       (make_pte_t *)_paravirt_ident_64
> > +#define paravirt_native_pte_val                (pte_val_t *)_paravirt_ident_64
> > +
> > +#define paravirt_native_make_pmd       (make_pmd_t *)_paravirt_ident_64
> > +#define paravirt_native_pmd_val                (pmd_val_t *)_paravirt_ident_64
> > +
> > +#define paravirt_native_make_pud       (make_pud_t *)_paravirt_ident_64
> > +#define paravirt_native_pud_val                (pud_val_t *)_paravirt_ident_64
> > +
> > +#define paravirt_native_make_pgd       (make_pgd_t *)_paravirt_ident_64
> > +#define paravirt_native_pgd_val                (pgd_val_t *)_paravirt_ident_64
> > +#endif
> >     
> I think I prefer:
>
> /* make_pte etc and pgd_val etc are identity functions. */
> #define paravirt_native_page_op \
>         (sizeof(pte_t) == sizeof(u64) ? paravirt_ident_64 : paravirt_ident_32)
>
> Then use that everywhere rather than these defines?
>   
They disappear later in the series anyway.

> But it's a minor point; the code seems perfectly sound.
>   
Great, thanks for reviewing.

   J

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