Re: [patch 10/21] Xen-paravirt: add hooks to intercept mm creation and destruction

Jeremy Fitzhardinge
2007-02-16T06:55:34Z

Andrew Morton wrote:
> On Thu, 15 Feb 2007 18:24:59 -0800 Jeremy Fitzhardinge <jeremy@goop.org> wrote:
>
>
>> Add hooks to allow a paravirt implementation to track the lifetime of
>> an mm.
>>
>> --- a/arch/i386/kernel/paravirt.c
>> +++ b/arch/i386/kernel/paravirt.c
>> @@ -706,6 +706,10 @@ struct paravirt_ops paravirt_ops = {
>> .irq_enable_sysexit = native_irq_enable_sysexit,
>> .iret = native_iret,
>>
>> + .dup_mmap = (void *)native_nop,
>> + .exit_mmap = (void *)native_nop,
>> + .activate_mm = (void *)native_nop,
>> +
>> .startup_ipi_hook = (void *)native_nop,
>> };
>>
>
> eww. I suppose there's a good reason for the casting.
>

Yeah, it's a bit ugly. The alternative is to have a separate
correctly-typed nop function for each operation. But that's even more
typing.

> It seems strange to call out to arch_foo() from within an arch header file.
> I mean, we implicity know we're i386.
>
> Maybe it's just poorly named.
>

The other two are arch_* and are called from common code.
arch_activate_mm() is either empty or a call to
paravirt_ops.activate_mm. I could name it paravirt_activate_mm (as it
was in earlier versions of this patch), but then it would be
inconsistent with the other functions. I thought the consistency was
more important, because these calls need to be properly matched.

>> +static inline void paravirt_activate_mm(struct mm_struct *prev,
>> + struct mm_struct *next)
>> +{
>> +}
>> +
>> +static inline void paravirt_dup_mmap(struct mm_struct *oldmm,
>> + struct mm_struct *mm)
>> +{
>> +}
>> +
>> +static inline void paravirt_exit_mmap(struct mm_struct *mm)
>> +{
>> +}
>>
>
> These functions are unreferenced in this patchset.
>

OK, I'll drop them.

>> #endif /* CONFIG_PARAVIRT */
>> #endif /* __ASM_PARAVIRT_H */
>> ===================================================================
>> --- a/include/linux/sched.h
>> +++ b/include/linux/sched.h
>> @@ -374,6 +374,12 @@ struct mm_struct {
>> rwlock_t ioctx_list_lock;
>> struct kioctx *ioctx_list;
>> };
>> +
>> +#ifndef __HAVE_ARCH_MM_LIFETIME
>> +#define arch_activate_mm(prev, next) do {} while(0)
>> +#define arch_dup_mmap(oldmm, mm) do {} while(0)
>> +#define arch_exit_mmap(mm) do {} while(0)
>> +#endif
>>
>
> Can we lose __HAVE_ARCH_MM_LIFETIME? Just define these (preferably in C,
> not in cpp) in the appropriate include/asm-foo/ files?
>

I guess, if you want. For everything except i386 (and x86_64 in the not
too distant future) they'll be noops. But for consistency, I/we would
have to put the appropriate arch_activate_mm() into each arch's
activate_mm(); I seem to remember some were not as straightforward as i386.

>> struct sighand_struct {
>> atomic_t count;
>> ===================================================================
>> --- a/kernel/fork.c
>> +++ b/kernel/fork.c
>> @@ -286,6 +286,7 @@ static inline int dup_mmap(struct mm_str
>> if (retval)
>> goto out;
>> }
>> + arch_dup_mmap(oldmm, mm);
>> retval = 0;
>> out:
>> up_write(&mm->mmap_sem);
>> ===================================================================
>> --- a/mm/mmap.c
>> +++ b/mm/mmap.c
>> @@ -1976,6 +1976,8 @@ void exit_mmap(struct mm_struct *mm)
>> struct vm_area_struct *vma = mm->mmap;
>> unsigned long nr_accounted = 0;
>> unsigned long end;
>> +
>> + arch_exit_mmap(mm);
>>
>> lru_add_drain();
>> flush_cache_mm(mm);
>>
>
> Perhaps some commentary telling the arch maintainer what these hooks he's
> being offered are for?
>

OK.

J