Izik Eidus wrote:
> Izik Eidus wrote:
>> Anthony Liguori wrote:
>>> Izik Eidus wrote:
>>>>
>>>> @@ -1058,8 +1038,27 @@ struct page *gfn_to_page(struct kvm *kvm,
>>>> gfn_t gfn)
>>>>
>>>> gfn = unalias_gfn(kvm, gfn);
>>>> slot = __gfn_to_memslot(kvm, gfn);
>>>> - if (!slot)
>>>> + if (!slot) {
>>>> + get_page(bad_page);
>>>> return bad_page;
>>>> + }
>>>> + if (slot->user_alloc) {
>>>> + struct page *page[1];
>>>> + int npages;
>>>> +
>>>> + down_read(¤t->mm->mmap_sem);
>>>> + npages = get_user_pages(current, current->mm,
>>>> + slot->userspace_addr
>>>> + + (gfn - slot->base_gfn) * PAGE_SIZE, 1,
>>>> + 1, 0, page, NULL);
>>>> + up_read(¤t->mm->mmap_sem);
>>>> + if (npages != 1) {
>>>> + get_page(bad_page);
>>>> + return bad_page;
>>>> + }
>>>> + return page[0];
>>>>
>>>
>>> Wouldn't it be necessary to assign page[0] to slot->phys_mem[gfn -
>>> slot->base_gfn]?
>>
> sorry, it seems like i missunderstand you in the answer i gave you.
> it wouldnt be necessary to assign page[0] to slot->phys_mem[gfn -
> slot->base_gfn], beacuse phys_mem wont have any memory allocate by
> this time.
>
> with this patch, we are not holding anymore (when using userspace
> allocation) array of all the memory at phys_mem.
> beacuse now that the pages are swappable, the physical address pointed
> by the virtual address all the time change (for example when swapping
> happn)
> so no one promise us that slot->phys_mem[gfn - slot->base_gfn] will
> really point to page holding the gfn page.
>
> so what we did, is throw away the phys_mem array (also nice beacuse it
> waste less ram), and at runtime we are getting the pages by using the
> virtual address
> beacuse the reference of the page get increased, it promised us that
> untill we release it point to the gfn (release it by doing put_page)
>
> hope i was more clear this time :)
Yes, that makes sense!
I wonder if there's a more elegant way dealing with older userspaces.
For instance, is there any reason why we can allocate a userspace memory
region on behalf of userspace. That way swap would even work with older
userspaces.
Regards,
Anthony Liguori
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