Re: [patch 02/13] KVM: MMU: switch to get_user_pages_fast

[Avi Kivity <avi@qumranet.com>]

Marcelo Tosatti wrote:
>>
>>>   static int kvm_vm_fault(struct vm_area_struct *vma, struct vm_fault 
>>> *vmf)
>>>  {
>>> +	struct page *page[1];
>>> +	unsigned long addr;
>>> +	int npages;
>>> +	gfn_t gfn = vmf->pgoff;
>>>  	struct kvm *kvm = vma->vm_file->private_data;
>>> -	struct page *page;
>>>  -	if (!kvm_is_visible_gfn(kvm, vmf->pgoff))
>>> +	addr = gfn_to_hva(kvm, gfn);
>>> +	if (kvm_is_error_hva(addr))
>>>  		return VM_FAULT_SIGBUS;
>>> -	page = gfn_to_page(kvm, vmf->pgoff);
>>> -	if (is_error_page(page)) {
>>> -		kvm_release_page_clean(page);
>>> +
>>> +	npages = get_user_pages(current, current->mm, addr, 1, 1, 0, page,
>>> +				NULL);
>>> +	if (unlikely(npages != 1))
>>>  		return VM_FAULT_SIGBUS;
>>> -	}
>>> -	vmf->page = page;
>>> +
>>> +	vmf->page = page[0];
>>>  	return 0;
>>>  }
>>>    
>>>       
>> Why this change?
>>     
>
> Because get_user_pages_fast grabs mmap_sem if necessary, but ->vm_fault
> already holds it.
>
>   

Right.  I think it merits its own patch (and changelog entry) since it 
differs in spirit from the rest.

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