[PATCH] KVM: PPC: Book3S HV: Don't use compound_order to determine host mapping size

[Nicholas Piggin]

THP paths can defer splitting compound pages until after the actual
remap and TLB flushes to split a huge PMD/PUD. This causes radix
partition scope page table mappings to get out of synch with the host
qemu page table mappings.

This results in random memory corruption in the guest when running
with THP. The easiest way to reproduce is use KVM baloon to free up
a lot of memory in the guest and then shrink the balloon to give the
memory back, while some work is being done in the guest.

Cc: Paul Mackerras <paulus at ozlabs.org>
Cc: David Gibson <david at gibson.dropbear.id.au>
Cc: "Aneesh Kumar K.V" <aneesh.kumar at linux.ibm.com>
Cc: linuxppc-dev at lists.ozlabs.org
Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
---
 arch/powerpc/kvm/book3s_64_mmu_radix.c | 88 ++++++++++----------------
 1 file changed, 34 insertions(+), 54 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_64_mmu_radix.c b/arch/powerpc/kvm/book3s_64_mmu_radix.c
index 0af1c0aea1fe..d8792445d95a 100644
--- a/arch/powerpc/kvm/book3s_64_mmu_radix.c
+++ b/arch/powerpc/kvm/book3s_64_mmu_radix.c
@@ -525,8 +525,8 @@ int kvmppc_book3s_radix_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
 				   unsigned long ea, unsigned long dsisr)
 {
 	struct kvm *kvm = vcpu->kvm;
-	unsigned long mmu_seq, pte_size;
-	unsigned long gpa, gfn, hva, pfn;
+	unsigned long mmu_seq;
+	unsigned long gpa, gfn, hva;
 	struct kvm_memory_slot *memslot;
 	struct page *page = NULL;
 	long ret;
@@ -623,9 +623,10 @@ int kvmppc_book3s_radix_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
 	 */
 	hva = gfn_to_hva_memslot(memslot, gfn);
 	if (upgrade_p && __get_user_pages_fast(hva, 1, 1, &page) == 1) {
-		pfn = page_to_pfn(page);
 		upgrade_write = true;
 	} else {
+		unsigned long pfn;
+
 		/* Call KVM generic code to do the slow-path check */
 		pfn = __gfn_to_pfn_memslot(memslot, gfn, false, NULL,
 					   writing, upgrade_p);
@@ -639,63 +640,42 @@ int kvmppc_book3s_radix_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
 		}
 	}
 
-	/* See if we can insert a 1GB or 2MB large PTE here */
-	level = 0;
-	if (page && PageCompound(page)) {
-		pte_size = PAGE_SIZE << compound_order(compound_head(page));
-		if (pte_size >= PUD_SIZE &&
-		    (gpa & (PUD_SIZE - PAGE_SIZE)) ==
-		    (hva & (PUD_SIZE - PAGE_SIZE))) {
-			level = 2;
-			pfn &= ~((PUD_SIZE >> PAGE_SHIFT) - 1);
-		} else if (pte_size >= PMD_SIZE &&
-			   (gpa & (PMD_SIZE - PAGE_SIZE)) ==
-			   (hva & (PMD_SIZE - PAGE_SIZE))) {
-			level = 1;
-			pfn &= ~((PMD_SIZE >> PAGE_SHIFT) - 1);
-		}
-	}
-
 	/*
-	 * Compute the PTE value that we need to insert.
+	 * Read the PTE from the process' radix tree and use that
+	 * so we get the shift and attribute bits.
 	 */
-	if (page) {
-		pgflags = _PAGE_READ | _PAGE_EXEC | _PAGE_PRESENT | _PAGE_PTE |
-			_PAGE_ACCESSED;
-		if (writing || upgrade_write)
-			pgflags |= _PAGE_WRITE | _PAGE_DIRTY;
-		pte = pfn_pte(pfn, __pgprot(pgflags));
+	local_irq_disable();
+	ptep = __find_linux_pte(vcpu->arch.pgdir, hva, NULL, &shift);
+	pte = *ptep;
+	local_irq_enable();
+
+	/* Get pte level from shift/size */
+	if (shift == PUD_SHIFT &&
+	    (gpa & (PUD_SIZE - PAGE_SIZE)) ==
+	    (hva & (PUD_SIZE - PAGE_SIZE))) {
+		level = 2;
+	} else if (shift == PMD_SHIFT &&
+		   (gpa & (PMD_SIZE - PAGE_SIZE)) ==
+		   (hva & (PMD_SIZE - PAGE_SIZE))) {
+		level = 1;
 	} else {
-		/*
-		 * Read the PTE from the process' radix tree and use that
-		 * so we get the attribute bits.
-		 */
-		local_irq_disable();
-		ptep = __find_linux_pte(vcpu->arch.pgdir, hva, NULL, &shift);
-		pte = *ptep;
-		local_irq_enable();
-		if (shift == PUD_SHIFT &&
-		    (gpa & (PUD_SIZE - PAGE_SIZE)) ==
-		    (hva & (PUD_SIZE - PAGE_SIZE))) {
-			level = 2;
-		} else if (shift == PMD_SHIFT &&
-			   (gpa & (PMD_SIZE - PAGE_SIZE)) ==
-			   (hva & (PMD_SIZE - PAGE_SIZE))) {
-			level = 1;
-		} else if (shift && shift != PAGE_SHIFT) {
-			/* Adjust PFN */
-			unsigned long mask = (1ul << shift) - PAGE_SIZE;
-			pte = __pte(pte_val(pte) | (hva & mask));
-		}
-		pte = __pte(pte_val(pte) | _PAGE_EXEC | _PAGE_ACCESSED);
-		if (writing || upgrade_write) {
-			if (pte_val(pte) & _PAGE_WRITE)
-				pte = __pte(pte_val(pte) | _PAGE_DIRTY);
-		} else {
-			pte = __pte(pte_val(pte) & ~(_PAGE_WRITE | _PAGE_DIRTY));
+		level = 0;
+
+		/* Can not cope with unknown page shift */
+		if (shift && shift != PAGE_SHIFT) {
+			WARN_ON_ONCE(1);
+			return -EFAULT;
 		}
 	}
 
+	pte = __pte(pte_val(pte) | _PAGE_EXEC | _PAGE_ACCESSED);
+	if (writing || upgrade_write) {
+		if (pte_val(pte) & _PAGE_WRITE)
+			pte = __pte(pte_val(pte) | _PAGE_DIRTY);
+	} else {
+		pte = __pte(pte_val(pte) & ~(_PAGE_WRITE | _PAGE_DIRTY));
+	}
+
 	/* Allocate space in the tree and write the PTE */
 	ret = kvmppc_create_pte(kvm, pte, gpa, level, mmu_seq);
 
-- 
2.18.0