Re: [kvm-devel] [PATCH] Handle vma regions with no backing page (v2)

[Avi K. <av...@qu...>]

Muli Ben-Yehuda wrote:
>> @@ -544,19 +545,35 @@ pfn_t gfn_to_pfn(struct kvm *kvm, gfn_t gfn)
>>  	npages = get_user_pages(current, current->mm, addr, 1, 1, 1, page,
>>  				NULL);
>>  
>> -	if (npages != 1) {
>> -		get_page(bad_page);
>> -		return page_to_pfn(bad_page);
>> -	}
>> +	if (unlikely(npages != 1)) {
>> +		struct vm_area_struct *vma;
>>  
>> -	return page_to_pfn(page[0]);
>> +		vma = find_vma(current->mm, addr);
>> +		if (vma == NULL || addr >= vma->vm_start ||
>> +		    !(vma->vm_flags & VM_PFNMAP)) {
>>     
>
> Isn't the check for addr backwards here? For the VMA we would like to
> to find, vma->vm_start <= addr < vma->vm_end.
>
>   

The code is not trying to find a vma for the address, but a vma for the 
address which also has VM_PFNMAP set. The cases for vma not found, or 
vma found, but not VM_PFNMAP, are folded together.

-- 
Any sufficiently difficult bug is indistinguishable from a feature.