On Tue, Aug 10, 2021 at 3:32 PM Jing Zhang <jingzhangos@xxxxxxxxxx> wrote:
>
> Add a generic VM stats dirty_pages to record the number of dirty pages
> reflected in dirty_bitmap at the moment.
>
> Original-by: Peter Feiner <pfeiner@xxxxxxxxxx>
> Signed-off-by: Jing Zhang <jingzhangos@xxxxxxxxxx>
> ---
> arch/powerpc/kvm/book3s_64_mmu_hv.c | 8 ++++++--
> arch/powerpc/kvm/book3s_64_mmu_radix.c | 1 +
> arch/powerpc/kvm/book3s_hv_rm_mmu.c | 1 +
> include/linux/kvm_host.h | 3 ++-
> include/linux/kvm_types.h | 1 +
> virt/kvm/kvm_main.c | 26 +++++++++++++++++++++++---
> 6 files changed, 34 insertions(+), 6 deletions(-)
>
> diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> index c63e263312a4..e4aafa10efa1 100644
> --- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
> +++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
> @@ -1122,8 +1122,10 @@ long kvmppc_hv_get_dirty_log_hpt(struct kvm *kvm,
> * since we always put huge-page HPTEs in the rmap chain
> * corresponding to their page base address.
> */
> - if (npages)
> + if (npages) {
> set_dirty_bits(map, i, npages);
> + kvm->stat.generic.dirty_pages += npages;
> + }
> ++rmapp;
> }
> preempt_enable();
> @@ -1178,8 +1180,10 @@ void kvmppc_unpin_guest_page(struct kvm *kvm, void *va, unsigned long gpa,
> gfn = gpa >> PAGE_SHIFT;
> srcu_idx = srcu_read_lock(&kvm->srcu);
> memslot = gfn_to_memslot(kvm, gfn);
> - if (memslot && memslot->dirty_bitmap)
> + if (memslot && memslot->dirty_bitmap) {
> set_bit_le(gfn - memslot->base_gfn, memslot->dirty_bitmap);
> + ++kvm->stat.generic.dirty_pages;
> + }
> srcu_read_unlock(&kvm->srcu, srcu_idx);
> }
>
> diff --git a/arch/powerpc/kvm/book3s_64_mmu_radix.c b/arch/powerpc/kvm/book3s_64_mmu_radix.c
> index b5905ae4377c..3a6cb3854a44 100644
> --- a/arch/powerpc/kvm/book3s_64_mmu_radix.c
> +++ b/arch/powerpc/kvm/book3s_64_mmu_radix.c
> @@ -1150,6 +1150,7 @@ long kvmppc_hv_get_dirty_log_radix(struct kvm *kvm,
> j = i + 1;
> if (npages) {
> set_dirty_bits(map, i, npages);
> + kvm->stat.generic.dirty_pages += npages;
> j = i + npages;
> }
> }
> diff --git a/arch/powerpc/kvm/book3s_hv_rm_mmu.c b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
> index 632b2545072b..16806bc473fa 100644
> --- a/arch/powerpc/kvm/book3s_hv_rm_mmu.c
> +++ b/arch/powerpc/kvm/book3s_hv_rm_mmu.c
> @@ -109,6 +109,7 @@ void kvmppc_update_dirty_map(const struct kvm_memory_slot *memslot,
> npages = (psize + PAGE_SIZE - 1) / PAGE_SIZE;
> gfn -= memslot->base_gfn;
> set_dirty_bits_atomic(memslot->dirty_bitmap, gfn, npages);
> + kvm->stat.generic.dirty_pages += npages;
> }
> EXPORT_SYMBOL_GPL(kvmppc_update_dirty_map);
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index f50bfcf225f0..1e8e66fb915b 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -1421,7 +1421,8 @@ struct _kvm_stats_desc {
> KVM_STATS_BASE_POW10, -9)
>
> #define KVM_GENERIC_VM_STATS() \
> - STATS_DESC_COUNTER(VM_GENERIC, remote_tlb_flush)
> + STATS_DESC_COUNTER(VM_GENERIC, remote_tlb_flush), \
> + STATS_DESC_COUNTER(VM_GENERIC, dirty_pages)
>
> #define KVM_GENERIC_VCPU_STATS() \
> STATS_DESC_COUNTER(VCPU_GENERIC, halt_successful_poll), \
> diff --git a/include/linux/kvm_types.h b/include/linux/kvm_types.h
> index ed6a985c5680..6c05df00aebf 100644
> --- a/include/linux/kvm_types.h
> +++ b/include/linux/kvm_types.h
> @@ -78,6 +78,7 @@ struct kvm_mmu_memory_cache {
>
> struct kvm_vm_stat_generic {
> u64 remote_tlb_flush;
> + u64 dirty_pages;
> };
>
> struct kvm_vcpu_stat_generic {
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index a438a7a3774a..93f0ca2ea326 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1228,6 +1228,19 @@ static int kvm_alloc_dirty_bitmap(struct kvm_memory_slot *memslot)
> return 0;
> }
>
> +static inline unsigned long hweight_dirty_bitmap(
> + struct kvm_memory_slot *memslot)
> +{
> + unsigned long i;
> + unsigned long count = 0;
> + unsigned long n = kvm_dirty_bitmap_bytes(memslot);
> +
> + for (i = 0; i < n / sizeof(long); ++i)
> + count += hweight_long(memslot->dirty_bitmap[i]);
> +
> + return count;
> +}
> +
> /*
> * Delete a memslot by decrementing the number of used slots and shifting all
> * other entries in the array forward one spot.
> @@ -1612,6 +1625,7 @@ static int kvm_delete_memslot(struct kvm *kvm,
> if (r)
> return r;
>
> + kvm->stat.generic.dirty_pages -= hweight_dirty_bitmap(old);
> kvm_free_memslot(kvm, old);
> return 0;
> }
> @@ -1733,8 +1747,10 @@ int __kvm_set_memory_region(struct kvm *kvm,
> if (r)
> goto out_bitmap;
>
> - if (old.dirty_bitmap && !new.dirty_bitmap)
> + if (old.dirty_bitmap && !new.dirty_bitmap) {
> + kvm->stat.generic.dirty_pages -= hweight_dirty_bitmap(&old);
> kvm_destroy_dirty_bitmap(&old);
> + }
> return 0;
>
> out_bitmap:
> @@ -1895,6 +1911,7 @@ static int kvm_get_dirty_log_protect(struct kvm *kvm, struct kvm_dirty_log *log)
> offset = i * BITS_PER_LONG;
> kvm_arch_mmu_enable_log_dirty_pt_masked(kvm, memslot,
> offset, mask);
> + kvm->stat.generic.dirty_pages -= hweight_long(mask);
> }
> KVM_MMU_UNLOCK(kvm);
> }
> @@ -2012,6 +2029,7 @@ static int kvm_clear_dirty_log_protect(struct kvm *kvm,
> flush = true;
> kvm_arch_mmu_enable_log_dirty_pt_masked(kvm, memslot,
> offset, mask);
> + kvm->stat.generic.dirty_pages -= hweight_long(mask);
> }
> }
> KVM_MMU_UNLOCK(kvm);
> @@ -3062,11 +3080,13 @@ void mark_page_dirty_in_slot(struct kvm *kvm,
> unsigned long rel_gfn = gfn - memslot->base_gfn;
> u32 slot = (memslot->as_id << 16) | memslot->id;
>
> - if (kvm->dirty_ring_size)
> + if (kvm->dirty_ring_size) {
> kvm_dirty_ring_push(kvm_dirty_ring_get(kvm),
> slot, rel_gfn);
> - else
> + } else {
> set_bit_le(rel_gfn, memslot->dirty_bitmap);
> + ++kvm->stat.generic.dirty_pages;
Couple of problems here:
- Calls to mark_page_dirty_in_slot aren't serialized by the mmu_lock,
so these updates will race.
- The page might already be dirty in the bitmap, so you're potentially
double counting here
You can fix both of these problems by changing set_bit_le to a
test_and_set_bit_le (might not be the function name -- but you get the
idea) and conditionally incrementing dirty_pages.
> + }
> }
> }
> EXPORT_SYMBOL_GPL(mark_page_dirty_in_slot);
>
> base-commit: d0732b0f8884d9cc0eca0082bbaef043f3fef7fb
> --
> 2.32.0.605.g8dce9f2422-goog
>
