Re: [patch 3/5] KVM: add kvm_follow_page()

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Marcelo Tosatti wrote:
> It can acquire the pagetablelock in the callback handler. But then,
> vm_normal_page() must also be exported.
>
> Are you guys OK with this ?
>
>   

Seems to me that requires fairly detailed mucking in mm details, just to 
get at a page.

I believe that a new get_users_pages_inatomic() is more suitable; 
Andrew, I'll write it if you agree.  Alternatively, walk_page_range() 
should take the lock itself, otherwise it is only usable if you don't 
care about correctness?

>  
> +static int kvm_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
> +		           void *private)
> +{
> +	struct page **page = private;
> +	struct vm_area_struct *vma;
> +	pte_t *ptep, pte;
> +	spinlock_t *ptl;
> +	int err = -EFAULT;
> +
> +	vma = find_vma(current->mm, addr);
> +	if (!vma)
> +		return err;
> +
> +	ptep = pte_offset_map_lock(current->mm, pmd, addr, &ptl);
> +	pte = *ptep;
> +	if (!pte_present(pte))
> +		goto unlock;
> +
> +	*page = vm_normal_page(vma, addr, pte);
> +	if (!*page)
> +		goto unlock;
> +
> +	get_page(*page);
> +	err = 0;
> +unlock:
> +	pte_unmap_unlock(ptep, ptl);
> +	return err;
> +}
> +
>   

See what one has to write to get at a page?  Unreasonable IMO.  And 
that's without hugetlb support AFAICT (kvm will want that soon).

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


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