On Thu, Mar 10, 2022 at 10:09:09PM +0800, Chao Peng wrote:
> KVM gets notified when memory pages changed in the memory backing store.
> When userspace allocates the memory with fallocate() or frees memory
> with fallocate(FALLOC_FL_PUNCH_HOLE), memory backing store calls into
> KVM fallocate/invalidate callbacks respectively. To ensure KVM never
> maps both the private and shared variants of a GPA into the guest, in
> the fallocate callback, we should zap the existing shared mapping and
> in the invalidate callback we should zap the existing private mapping.
>
> In the callbacks, KVM firstly converts the offset range into the
> gfn_range and then calls existing kvm_unmap_gfn_range() which will zap
> the shared or private mapping. Both callbacks pass in a memslot
> reference but we need 'kvm' so add a reference in memslot structure.
>
> Signed-off-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
> Signed-off-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
> ---
> include/linux/kvm_host.h | 3 ++-
> virt/kvm/kvm_main.c | 36 ++++++++++++++++++++++++++++++++++++
> 2 files changed, 38 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 9b175aeca63f..186b9b981a65 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -236,7 +236,7 @@ bool kvm_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
> int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu);
> #endif
>
> -#ifdef KVM_ARCH_WANT_MMU_NOTIFIER
> +#if defined(KVM_ARCH_WANT_MMU_NOTIFIER) || defined(CONFIG_MEMFILE_NOTIFIER)
> struct kvm_gfn_range {
> struct kvm_memory_slot *slot;
> gfn_t start;
> @@ -568,6 +568,7 @@ struct kvm_memory_slot {
> loff_t private_offset;
> struct memfile_pfn_ops *pfn_ops;
> struct memfile_notifier notifier;
> + struct kvm *kvm;
> };
>
> static inline bool kvm_slot_is_private(const struct kvm_memory_slot *slot)
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 67349421eae3..52319f49d58a 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -841,8 +841,43 @@ static int kvm_init_mmu_notifier(struct kvm *kvm)
> #endif /* CONFIG_MMU_NOTIFIER && KVM_ARCH_WANT_MMU_NOTIFIER */
>
> #ifdef CONFIG_MEMFILE_NOTIFIER
> +static void kvm_memfile_notifier_handler(struct memfile_notifier *notifier,
> + pgoff_t start, pgoff_t end)
> +{
> + int idx;
> + struct kvm_memory_slot *slot = container_of(notifier,
> + struct kvm_memory_slot,
> + notifier);
> + struct kvm_gfn_range gfn_range = {
> + .slot = slot,
> + .start = start - (slot->private_offset >> PAGE_SHIFT),
> + .end = end - (slot->private_offset >> PAGE_SHIFT),
> + .may_block = true,
> + };
> + struct kvm *kvm = slot->kvm;
> +
> + gfn_range.start = max(gfn_range.start, slot->base_gfn);
> + gfn_range.end = min(gfn_range.end, slot->base_gfn + slot->npages);
> +
> + if (gfn_range.start >= gfn_range.end)
> + return;
> +
> + idx = srcu_read_lock(&kvm->srcu);
> + KVM_MMU_LOCK(kvm);
> + kvm_unmap_gfn_range(kvm, &gfn_range);
> + kvm_flush_remote_tlbs(kvm);
> + KVM_MMU_UNLOCK(kvm);
> + srcu_read_unlock(&kvm->srcu, idx);
Should this also invalidate gfn_to_pfn_cache mappings? Otherwise it seems
possible the kernel might end up inadvertantly writing to now-private guest
memory via a now-stale gfn_to_pfn_cache entry.
