KVM: PPC: Book3S HV: Fix physical address calculations

This fixes a bug in kvmppc_do_h_enter() where the physical address
for a page can be calculated incorrectly if transparent huge pages
(THP) are active.  Until THP came along, it was true that if we
encountered a large (16M) page in kvmppc_do_h_enter(), then the
associated memslot must be 16M aligned for both its guest physical
address and the userspace address, and the physical address
calculations in kvmppc_do_h_enter() assumed that.  With THP, that
is no longer true.

In the case where we are using MMU notifiers and the page size that
we get from the Linux page tables is larger than the page being mapped
by the guest, we need to fill in some low-order bits of the physical
address.  Without THP, these bits would be the same in the guest
physical address (gpa) and the host virtual address (hva).  With THP,
they can be different, and we need to use the bits from hva rather
than gpa.

In the case where we are not using MMU notifiers, the host physical
address we get from the memslot->arch.slot_phys[] array already
includes the low-order bits down to the PAGE_SIZE level, even if
we are using large pages.  Thus we can simplify the calculation in
this case to just add in the remaining bits in the case where
PAGE_SIZE is 64k and the guest is mapping a 4k page.

The same bug exists in kvmppc_book3s_hv_page_fault().  The basic fix
is to use psize (the page size from the HPTE) rather than pte_size
(the page size from the Linux PTE) when updating the HPTE low word
in r.  That means that pfn needs to be computed to PAGE_SIZE
granularity even if the Linux PTE is a huge page PTE.  That can be
arranged simply by doing the page_to_pfn() before setting page to
the head of the compound page.  If psize is less than PAGE_SIZE,
then we need to make sure we only update the bits from PAGE_SIZE
upwards, in order not to lose any sub-page offset bits in r.
On the other hand, if psize is greater than PAGE_SIZE, we need to
make sure we don't bring in non-zero low order bits in pfn, hence
we mask (pfn << PAGE_SHIFT) with ~(psize - 1).
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>

arch/powerpc/kvm/book3s_64_mmu_hv.c

@@ -665,6 +665,7 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
 			return -EFAULT;
 	} else {
 		page = pages[0];
+		pfn = page_to_pfn(page);
 		if (PageHuge(page)) {
 			page = compound_head(page);
 			pte_size <<= compound_order(page);
@@ -689,7 +690,6 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
 			}
 			rcu_read_unlock_sched();
 		}
-		pfn = page_to_pfn(page);
 	}
 
 	ret = -EFAULT;
@@ -707,8 +707,14 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
 		r = (r & ~(HPTE_R_W|HPTE_R_I|HPTE_R_G)) | HPTE_R_M;
 	}
 
-	/* Set the HPTE to point to pfn */
-	r = (r & ~(HPTE_R_PP0 - pte_size)) | (pfn << PAGE_SHIFT);
+	/*
+	 * Set the HPTE to point to pfn.
+	 * Since the pfn is at PAGE_SIZE granularity, make sure we
+	 * don't mask out lower-order bits if psize < PAGE_SIZE.
+	 */
+	if (psize < PAGE_SIZE)
+		psize = PAGE_SIZE;
+	r = (r & ~(HPTE_R_PP0 - psize)) | ((pfn << PAGE_SHIFT) & ~(psize - 1));
 	if (hpte_is_writable(r) && !write_ok)
 		r = hpte_make_readonly(r);
 	ret = RESUME_GUEST;

arch/powerpc/kvm/book3s_hv_rm_mmu.c

@@ -225,6 +225,7 @@ long kvmppc_do_h_enter(struct kvm *kvm, unsigned long flags,
 		is_io = pa & (HPTE_R_I | HPTE_R_W);
 		pte_size = PAGE_SIZE << (pa & KVMPPC_PAGE_ORDER_MASK);
 		pa &= PAGE_MASK;
+		pa |= gpa & ~PAGE_MASK;
 	} else {
 		/* Translate to host virtual address */
 		hva = __gfn_to_hva_memslot(memslot, gfn);
@@ -238,13 +239,12 @@ long kvmppc_do_h_enter(struct kvm *kvm, unsigned long flags,
 				ptel = hpte_make_readonly(ptel);
 			is_io = hpte_cache_bits(pte_val(pte));
 			pa = pte_pfn(pte) << PAGE_SHIFT;
+			pa |= hva & (pte_size - 1);
 		}
 	}
 
 	if (pte_size < psize)
 		return H_PARAMETER;
-	if (pa && pte_size > psize)
-		pa |= gpa & (pte_size - 1);
 
 	ptel &= ~(HPTE_R_PP0 - psize);
 	ptel |= pa;