Anthony Liguori wrote:
> Now that we have userspace memory allocation, I wanted to play with
> ballooning.
> The idea is that when a guest "balloons" down, we simply unpin the underlying
> physical memory and the host kernel may or may not swap it. To reclaim
> ballooned memory, the guest can just start using it and we'll pin it on
> demand.
>
> The following patch is a stab at providing the right infrastructure for
> pinning
> and automatic repinning. I don't have a lot of comfort in the MMU code so I
> thought I'd get some feedback before going much further.
>
> gpa_to_hpa is a little awkward to hook, but it seems like the right place in
> the
> code. I'm most uncertain about the SMP safety of the unpinning. Presumably,
> I have to hold the kvm lock around the mmu_unshadow and page_cache release to
> ensure that another VCPU doesn't fault the page back in after mmu_unshadow?
>
> Feedback would be greatly appreciated!
>
> diff --git a/drivers/kvm/kvm.h b/drivers/kvm/kvm.h
> index 4a52d6e..8abe770 100644
> --- a/drivers/kvm/kvm.h
> +++ b/drivers/kvm/kvm.h
> @@ -409,6 +409,7 @@ struct kvm_memory_slot {
> unsigned long *rmap;
> unsigned long *dirty_bitmap;
> int user_alloc; /* user allocated memory */
> + unsigned long userspace_addr;
> };
>
> struct kvm {
> @@ -652,6 +653,7 @@ int kvm_mmu_unprotect_page_virt(struct kvm_vcpu *vcpu,
> gva_t gva);
> void __kvm_mmu_free_some_pages(struct kvm_vcpu *vcpu);
> int kvm_mmu_load(struct kvm_vcpu *vcpu);
> void kvm_mmu_unload(struct kvm_vcpu *vcpu);
> +int kvm_mmu_unpin(struct kvm *kvm, gfn_t gfn);
>
> int kvm_emulate_hypercall(struct kvm_vcpu *vcpu);
>
> diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
> index a0f8366..74105d1 100644
> --- a/drivers/kvm/kvm_main.c
> +++ b/drivers/kvm/kvm_main.c
> @@ -774,6 +774,7 @@ static int kvm_vm_ioctl_set_memory_region(struct kvm *kvm,
> unsigned long pages_num;
>
> new.user_alloc = 1;
> + new.userspace_addr = mem->userspace_addr;
> down_read(¤t->mm->mmap_sem);
>
> pages_num = get_user_pages(current, current->mm,
> @@ -1049,12 +1050,36 @@ struct kvm_memory_slot *gfn_to_memslot(struct kvm
> *kvm, gfn_t gfn)
> struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn)
> {
> struct kvm_memory_slot *slot;
> + struct page *page;
> + uint64_t slot_index;
>
> gfn = unalias_gfn(kvm, gfn);
> slot = __gfn_to_memslot(kvm, gfn);
> if (!slot)
> return NULL;
> - return slot->phys_mem[gfn - slot->base_gfn];
> +
> + slot_index = gfn - slot->base_gfn;
> + page = slot->phys_mem[slot_index];
> + if (unlikely(page == NULL)) {
> + unsigned long pages_num;
> +
> + down_read(¤t->mm->mmap_sem);
> +
> + pages_num = get_user_pages(current, current->mm,
> + slot->userspace_addr +
> + (slot_index << PAGE_SHIFT),
> + 1, 1, 0, &slot->phys_mem[slot_index],
> + NULL);
> +
> + up_read(¤t->mm->mmap_sem);
> +
> + if (pages_num != 1)
> + page = NULL;
> + else
> + page = slot->phys_mem[slot_index];
> + }
> +
> + return page;
> }
> EXPORT_SYMBOL_GPL(gfn_to_page);
>
> diff --git a/drivers/kvm/mmu.c b/drivers/kvm/mmu.c
> index f52604a..1820816 100644
> --- a/drivers/kvm/mmu.c
> +++ b/drivers/kvm/mmu.c
> @@ -25,6 +25,7 @@
> #include <linux/mm.h>
> #include <linux/highmem.h>
> #include <linux/module.h>
> +#include <linux/pagemap.h>
>
> #include <asm/page.h>
> #include <asm/cmpxchg.h>
> @@ -820,6 +821,33 @@ static void mmu_unshadow(struct kvm *kvm, gfn_t gfn)
> }
> }
>
> +int kvm_mmu_unpin(struct kvm *kvm, gfn_t gfn)
> +{
> + struct kvm_memory_slot *slot;
> + struct page *page;
> +
> + /* FIXME for each active vcpu */
> +
> + gfn = unalias_gfn(kvm, gfn);
> + slot = gfn_to_memslot(kvm, gfn);
> + if (!gfn)
> + return -EINVAL;
> +
> + /* FIXME: do we need to hold a lock here? */
> +
> + /* Remove page from shadow MMU and unpin page */
> + mmu_unshadow(kvm, gfn);
> + page = slot->phys_mem[gfn - slot->base_gfn];
> + if (page) {
> + if (!PageReserved(page))
> + SetPageDirty(page);
> + page_cache_release(page);
> + slot->phys_mem[gfn - slot->base_gfn] = NULL;
> + }
> +
> + return 0;
> +}
> +
> static void page_header_update_slot(struct kvm *kvm, void *pte, gpa_t gpa)
> {
> int slot = memslot_id(kvm, gfn_to_memslot(kvm, gpa >> PAGE_SHIFT));
>
> -------------------------------------------------------------------------
>
kvm_memory_slot
heh, i am working on similir patch, and our gfn_to_page and the change
to kvm_memory_slot even by varible names :)
few things you have to do to make this work:
make gfn_to_page safe always function (return bad_page in case of
failure, i have patch for this if you want)
hacking the kvm_read_guest_page / kvm_write_guest_page
kvm_clear_guest_page to do put_page after the usage of the page
secoend, is hacking the rmap to do reverse mapping to every present pte
and put_page() the pages at rmap_remove()
and this about all, to make this work.
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