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

[Anthony L. <an...@co...>]

Muli Ben-Yehuda wrote:
> On Tue, Apr 29, 2008 at 02:09:20PM -0500, Anthony Liguori wrote:
>   
>> This patch allows VMA's that contain no backing page to be used for guest
>> memory.  This is a drop-in replacement for Ben-Ami's first page in his direct
>> mmio series.  Here, we continue to allow mmio pages to be represented in the
>> rmap.
>>
>> Since v1, I've taken into account Andrea's suggestions at using VM_PFNMAP
>> instead of VM_IO and changed the BUG_ON to a return of bad_page.
>>
>> Signed-off-by: Anthony Liguori <ali...@us...>
>>
>> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
>> index 1d7991a..64e5efe 100644
>> --- a/virt/kvm/kvm_main.c
>> +++ b/virt/kvm/kvm_main.c
>> @@ -532,6 +532,7 @@ pfn_t gfn_to_pfn(struct kvm *kvm, gfn_t gfn)
>>  	struct page *page[1];
>>  	unsigned long addr;
>>  	int npages;
>> +	pfn_t pfn;
>>  
>>  	might_sleep();
>>  
>> @@ -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.
>   

Yes it is.  Thanks for spotting that.

Regards,

Anthony Liguori

> Cheers,
> Muli
>
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