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Subject[PATCH 2/4] KVM: Avoid checking huge page mappings in get_dirty_log()
Dropped such mappings when we enabled dirty logging and we will never
create new ones until we stop the logging.

For this we introduce a new function which can be used to write protect
a range of PT level pages: although we do not need to care about a range
of pages at this point, the following patch will need this feature to
optimize the write protection of many pages.

Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
---
arch/x86/include/asm/kvm_host.h | 5 ++-
arch/x86/kvm/mmu.c | 40 +++++++++++++++++++++++++++++---------
arch/x86/kvm/x86.c | 8 ++----
3 files changed, 36 insertions(+), 17 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 74c9edf..935cbcc 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -712,8 +712,9 @@ void kvm_mmu_set_mask_ptes(u64 user_mask, u64 accessed_mask,

int kvm_mmu_reset_context(struct kvm_vcpu *vcpu);
void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot);
-int kvm_mmu_rmap_write_protect(struct kvm *kvm, u64 gfn,
- struct kvm_memory_slot *slot);
+void kvm_mmu_write_protect_pt_masked(struct kvm *kvm,
+ struct kvm_memory_slot *slot,
+ gfn_t gfn_offset, unsigned long mask);
void kvm_mmu_zap_all(struct kvm *kvm);
unsigned int kvm_mmu_calculate_mmu_pages(struct kvm *kvm);
void kvm_mmu_change_mmu_pages(struct kvm *kvm, unsigned int kvm_nr_mmu_pages);
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 67857bd..be8a529 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -1037,27 +1037,47 @@ static int __rmap_write_protect(struct kvm *kvm, unsigned long *rmapp, int level
return write_protected;
}

-int kvm_mmu_rmap_write_protect(struct kvm *kvm, u64 gfn,
- struct kvm_memory_slot *slot)
+/**
+ * kvm_mmu_write_protect_pt_masked - write protect selected PT level pages
+ * @kvm: kvm instance
+ * @slot: slot to protect
+ * @gfn_offset: start of the BITS_PER_LONG pages we care about
+ * @mask: indicates which pages we should protect
+ *
+ * Used when we do not need to care about huge page mappings: e.g. during dirty
+ * logging we do not have any such mappings.
+ */
+void kvm_mmu_write_protect_pt_masked(struct kvm *kvm,
+ struct kvm_memory_slot *slot,
+ gfn_t gfn_offset, unsigned long mask)
{
unsigned long *rmapp;
- int i, write_protected = 0;

- for (i = PT_PAGE_TABLE_LEVEL;
- i < PT_PAGE_TABLE_LEVEL + KVM_NR_PAGE_SIZES; ++i) {
- rmapp = __gfn_to_rmap(gfn, i, slot);
- write_protected |= __rmap_write_protect(kvm, rmapp, i);
- }
+ while (mask) {
+ rmapp = &slot->rmap[gfn_offset + __ffs(mask)];
+ __rmap_write_protect(kvm, rmapp, PT_PAGE_TABLE_LEVEL);

- return write_protected;
+ /* clear the first set bit */
+ mask &= mask - 1;
+ }
}

static int rmap_write_protect(struct kvm *kvm, u64 gfn)
{
struct kvm_memory_slot *slot;
+ unsigned long *rmapp;
+ int i;
+ int write_protected = 0;

slot = gfn_to_memslot(kvm, gfn);
- return kvm_mmu_rmap_write_protect(kvm, gfn, slot);
+
+ for (i = PT_PAGE_TABLE_LEVEL;
+ i < PT_PAGE_TABLE_LEVEL + KVM_NR_PAGE_SIZES; ++i) {
+ rmapp = __gfn_to_rmap(gfn, i, slot);
+ write_protected |= __rmap_write_protect(kvm, rmapp, i);
+ }
+
+ return write_protected;
}

static int kvm_unmap_rmapp(struct kvm *kvm, unsigned long *rmapp,
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c9d99e5..3bc1922 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3069,13 +3069,11 @@ static void write_protect_slot(struct kvm *kvm,

/* Not many dirty pages compared to # of shadow pages. */
if (nr_dirty_pages < kvm->arch.n_used_mmu_pages) {
- unsigned long gfn_offset;
+ gfn_t offset;

- for_each_set_bit(gfn_offset, dirty_bitmap, memslot->npages) {
- unsigned long gfn = memslot->base_gfn + gfn_offset;
+ for_each_set_bit(offset, dirty_bitmap, memslot->npages)
+ kvm_mmu_write_protect_pt_masked(kvm, memslot, offset, 1);

- kvm_mmu_rmap_write_protect(kvm, gfn, memslot);
- }
kvm_flush_remote_tlbs(kvm);
} else
kvm_mmu_slot_remove_write_access(kvm, memslot->id);
--
1.7.5.4


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