[PATCH 2/4] KVM: PPC: Book3S HV: Map single pages when doing dirty page logging

[Paul Mackerras <paulus@ozlabs.org>]

For radix guests, this makes KVM map guest memory as individual pages
when dirty page logging is enabled for the memslot corresponding to the
guest real address.  Having a separate partition-scoped PTE for each
system page mapped to the guest means that we have a separate dirty
bit for each page, thus making the reported dirty bitmap more accurate.
Without this, if part of guest memory is backed by transparent huge
pages, the dirty status is reported at a 2MB granularity rather than
a 64kB (or 4kB) granularity for that part, causing userspace to have
to transmit more data when migrating the guest.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
---
 arch/powerpc/kvm/book3s_64_mmu_radix.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_64_mmu_radix.c b/arch/powerpc/kvm/book3s_64_mmu_radix.c
index d68162e..87ad35e 100644
--- a/arch/powerpc/kvm/book3s_64_mmu_radix.c
+++ b/arch/powerpc/kvm/book3s_64_mmu_radix.c
@@ -683,6 +683,7 @@ int kvmppc_book3s_instantiate_page(struct kvm_vcpu *vcpu,
 	pte_t pte, *ptep;
 	unsigned int shift, level;
 	int ret;
+	bool large_enable;
 
 	/* used to check for invalidations in progress */
 	mmu_seq = kvm->mmu_notifier_seq;
@@ -732,12 +733,15 @@ int kvmppc_book3s_instantiate_page(struct kvm_vcpu *vcpu,
 	pte = *ptep;
 	local_irq_enable();
 
+	/* If we're logging dirty pages, always map single pages */
+	large_enable = !(memslot->flags & KVM_MEM_LOG_DIRTY_PAGES);
+
 	/* Get pte level from shift/size */
-	if (shift = PUD_SHIFT &&
+	if (large_enable && shift = PUD_SHIFT &&
 	    (gpa & (PUD_SIZE - PAGE_SIZE)) =
 	    (hva & (PUD_SIZE - PAGE_SIZE))) {
 		level = 2;
-	} else if (shift = PMD_SHIFT &&
+	} else if (large_enable && shift = PMD_SHIFT &&
 		   (gpa & (PMD_SIZE - PAGE_SIZE)) =
 		   (hva & (PMD_SIZE - PAGE_SIZE))) {
 		level = 1;
-- 
2.7.4