On Mon, 2011-01-31 at 17:18 -0200, Marcelo Tosatti wrote:
> On Mon, Jan 24, 2011 at 10:37:56PM -0700, Alex Williamson wrote:
> > On Mon, 2011-01-24 at 08:44 -0700, Alex Williamson wrote:
> > > I'll look at how we might be
> > > able to allocate slots on demand. Thanks,
> >
> > Here's a first cut just to see if this looks agreeable. This allows the
> > slot array to grow on demand. This works with current userspace, as
> > well as userspace trivially modified to double KVMState.slots and
> > hotplugging enough pci-assign devices to exceed the previous limit (w/ &
> > w/o ept). Hopefully I got the rcu bits correct. Does this look like
> > the right path? If so, I'll work on removing the fixed limit from
> > userspace next. Thanks,
> >
> > Alex
> >
> >
> > kvm: Allow memory slot array to grow on demand
> >
> > Remove fixed KVM_MEMORY_SLOTS limit, allowing the slot array
> > to grow on demand. Private slots are now allocated at the
> > front instead of the end. Only x86 seems to use private slots,
> > so this is now zero for all other archs. The memslots pointer
> > is already updated using rcu, so changing the size off the
> > array when it's replaces is straight forward. x86 also keeps
> > a bitmap of slots used by a kvm_mmu_page, which requires a
> > shadow tlb flush whenever we increase the number of slots.
> > This forces the pages to be rebuilt with the new bitmap size.
> >
> > Signed-off-by: Alex Williamson <[email protected]>
> > ---
> >
> > arch/ia64/include/asm/kvm_host.h | 4 --
> > arch/ia64/kvm/kvm-ia64.c | 2 +
> > arch/powerpc/include/asm/kvm_host.h | 3 --
> > arch/s390/include/asm/kvm_host.h | 3 --
> > arch/x86/include/asm/kvm_host.h | 3 +-
> > arch/x86/include/asm/vmx.h | 6 ++-
> > arch/x86/kvm/mmu.c | 7 +++-
> > arch/x86/kvm/x86.c | 6 ++-
> > include/linux/kvm_host.h | 7 +++-
> > virt/kvm/kvm_main.c | 65
> > ++++++++++++++++++++++++-----------
> > 10 files changed, 63 insertions(+), 43 deletions(-)
[snip]
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index fd67bcd..32f023c 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
[snip]
> > @@ -752,12 +753,19 @@ skip_lpage:
> >
> > if (!npages) {
> > r = -ENOMEM;
> > - slots = kzalloc(sizeof(struct kvm_memslots), GFP_KERNEL);
> > +
> > + nmemslots = (mem->slot >= kvm->memslots->nmemslots) ?
> > + mem->slot + 1 : kvm->memslots->nmemslots;
> > +
> > + slots = kzalloc(sizeof(struct kvm_memslots) +
> > + nmemslots * sizeof(struct kvm_memory_slot),
> > + GFP_KERNEL);
> > if (!slots)
> > goto out_free;
> > - memcpy(slots, kvm->memslots, sizeof(struct kvm_memslots));
> > - if (mem->slot >= slots->nmemslots)
> > - slots->nmemslots = mem->slot + 1;
> > + memcpy(slots, kvm->memslots,
> > + sizeof(struct kvm_memslots) + kvm->memslots->nmemslots *
> > + sizeof(struct kvm_memory_slot));
> > + slots->nmemslots = nmemslots;
>
> Other than the upper limit, should disallow increasing the number of
> slots in case the new slot is being deleted (npages == 0). So none of
> this additions to !npages case should be necessary.
The existing code currently allows adding a slot with !npages. I'll
create a small separate patch to make this behavioral change.
> Also, must disallow shrinking the number of slots.
Right, we only grow, never shrink.
> > slots->generation++;
> > slots->memslots[mem->slot].flags |= KVM_MEMSLOT_INVALID;
> >
> > @@ -787,12 +795,21 @@ skip_lpage:
> > }
> >
> > r = -ENOMEM;
> > - slots = kzalloc(sizeof(struct kvm_memslots), GFP_KERNEL);
> > +
> > + if (mem->slot >= kvm->memslots->nmemslots) {
> > + nmemslots = mem->slot + 1;
> > + flush = true;
> > + } else
> > + nmemslots = kvm->memslots->nmemslots;
> > +
> > + slots = kzalloc(sizeof(struct kvm_memslots) +
> > + nmemslots * sizeof(struct kvm_memory_slot),
> > + GFP_KERNEL);
> > if (!slots)
> > goto out_free;
> > - memcpy(slots, kvm->memslots, sizeof(struct kvm_memslots));
> > - if (mem->slot >= slots->nmemslots)
> > - slots->nmemslots = mem->slot + 1;
> > + memcpy(slots, kvm->memslots, sizeof(struct kvm_memslots) +
> > + kvm->memslots->nmemslots * sizeof(struct kvm_memory_slot));
> > + slots->nmemslots = nmemslots;
> > slots->generation++;
> >
> > /* actual memory is freed via old in kvm_free_physmem_slot below */
> > @@ -808,6 +825,9 @@ skip_lpage:
> > rcu_assign_pointer(kvm->memslots, slots);
>
> It should be:
>
> spin_lock(kvm->mmu_lock)
> rcu_assign_pointer()
> kvm_arch_flush_shadow()
> spin_unlock(kvm->mmu_lock)
>
> But kvm_arch_flush_shadow() takes mmu_lock currently, so that needs
> fixing.
Hmm, I tried to follow the example in the !npages path just above this
that does:
rcu_assign_pointer()
synchronize_srcu_expedited()
kvm_arch_flush_shadow()
Do we have an existing issue there with mmu_lock? Thanks,
Alex
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