[PATCH resend 0/2] KVM: arm64: Unify stage2 mapping for THP backed memory

[PATCH resend 0/2] KVM: arm64: Unify stage2 mapping for THP backed memory

[Zenghui Yu]

This series was originally posted by Suzuki K Poulose a year ago [*],
with the aim of cleaning up the handling of the stage2 huge mapping for
THP. I think this still helps to make the current code cleaner, so
rebase it on top of kvmarm/master and repost it for acceptance.

Thanks!

[*] https://lore.kernel.org/kvm/1554909832-7169-1-git-send-email-suzuki.poulose@arm.com/

Suzuki K Poulose (2):
  KVM: arm64: Clean up the checking for huge mapping
  KVM: arm64: Unify handling THP backed host memory

 virt/kvm/arm/mmu.c | 121 ++++++++++++++++++++++++---------------------
 1 file changed, 65 insertions(+), 56 deletions(-)

-- 
2.19.1

[PATCH resend 1/2] KVM: arm64: Clean up the checking for huge mapping

[Zenghui Yu]

From: Suzuki K Poulose <suzuki.poulose@arm.com>

If we are checking whether the stage2 can map PAGE_SIZE,
we don't have to do the boundary checks as both the host
VMA and the guest memslots are page aligned. Bail the case
easily.

While we're at it, fixup a typo in the comment below.

Cc: Christoffer Dall <christoffer.dall@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
---
 virt/kvm/arm/mmu.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
index e3b9ee268823..557f36866d1c 100644
--- a/virt/kvm/arm/mmu.c
+++ b/virt/kvm/arm/mmu.c
@@ -1607,6 +1607,10 @@ static bool fault_supports_stage2_huge_mapping(struct kvm_memory_slot *memslot,
 	hva_t uaddr_start, uaddr_end;
 	size_t size;
 
+	/* The memslot and the VMA are guaranteed to be aligned to PAGE_SIZE */
+	if (map_size == PAGE_SIZE)
+		return true;
+
 	size = memslot->npages * PAGE_SIZE;
 
 	gpa_start = memslot->base_gfn << PAGE_SHIFT;
@@ -1626,7 +1630,7 @@ static bool fault_supports_stage2_huge_mapping(struct kvm_memory_slot *memslot,
 	 *    |abcde|fgh  Stage-1 block  |    Stage-1 block tv|xyz|
 	 *    +-----+--------------------+--------------------+---+
 	 *
-	 *    memslot->base_gfn << PAGE_SIZE:
+	 *    memslot->base_gfn << PAGE_SHIFT:
 	 *      +---+--------------------+--------------------+-----+
 	 *      |abc|def  Stage-2 block  |    Stage-2 block   |tvxyz|
 	 *      +---+--------------------+--------------------+-----+
-- 
2.19.1

[PATCH resend 2/2] KVM: arm64: Unify handling THP backed host memory

[Zenghui Yu]

From: Suzuki K Poulose <suzuki.poulose@arm.com>

We support mapping host memory backed by PMD transparent hugepages
at stage2 as huge pages. However the checks are now spread across
two different places. Let us unify the handling of the THPs to
keep the code cleaner (and future proof for PUD THP support).
This patch moves transparent_hugepage_adjust() closer to the caller
to avoid a forward declaration for fault_supports_stage2_huge_mappings().

Also, since we already handle the case where the host VA and the guest
PA may not be aligned, the explicit VM_BUG_ON() is not required.

Cc: Marc Zyngier <maz@kernel.org>
Cc: Christoffer Dall <christoffer.dall@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
---
 virt/kvm/arm/mmu.c | 115 +++++++++++++++++++++++----------------------
 1 file changed, 60 insertions(+), 55 deletions(-)

diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
index 557f36866d1c..93a770fd2b5e 100644
--- a/virt/kvm/arm/mmu.c
+++ b/virt/kvm/arm/mmu.c
@@ -1372,47 +1372,6 @@ int kvm_phys_addr_ioremap(struct kvm *kvm, phys_addr_t guest_ipa,
 	return ret;
 }
 
-static bool transparent_hugepage_adjust(kvm_pfn_t *pfnp, phys_addr_t *ipap)
-{
-	kvm_pfn_t pfn = *pfnp;
-	gfn_t gfn = *ipap >> PAGE_SHIFT;
-
-	if (kvm_is_transparent_hugepage(pfn)) {
-		unsigned long mask;
-		/*
-		 * The address we faulted on is backed by a transparent huge
-		 * page.  However, because we map the compound huge page and
-		 * not the individual tail page, we need to transfer the
-		 * refcount to the head page.  We have to be careful that the
-		 * THP doesn't start to split while we are adjusting the
-		 * refcounts.
-		 *
-		 * We are sure this doesn't happen, because mmu_notifier_retry
-		 * was successful and we are holding the mmu_lock, so if this
-		 * THP is trying to split, it will be blocked in the mmu
-		 * notifier before touching any of the pages, specifically
-		 * before being able to call __split_huge_page_refcount().
-		 *
-		 * We can therefore safely transfer the refcount from PG_tail
-		 * to PG_head and switch the pfn from a tail page to the head
-		 * page accordingly.
-		 */
-		mask = PTRS_PER_PMD - 1;
-		VM_BUG_ON((gfn & mask) != (pfn & mask));
-		if (pfn & mask) {
-			*ipap &= PMD_MASK;
-			kvm_release_pfn_clean(pfn);
-			pfn &= ~mask;
-			kvm_get_pfn(pfn);
-			*pfnp = pfn;
-		}
-
-		return true;
-	}
-
-	return false;
-}
-
 /**
  * stage2_wp_ptes - write protect PMD range
  * @pmd:	pointer to pmd entry
@@ -1660,6 +1619,59 @@ static bool fault_supports_stage2_huge_mapping(struct kvm_memory_slot *memslot,
 	       (hva & ~(map_size - 1)) + map_size <= uaddr_end;
 }
 
+/*
+ * Check if the given hva is backed by a transparent huge page (THP) and
+ * whether it can be mapped using block mapping in stage2. If so, adjust
+ * the stage2 PFN and IPA accordingly. Only PMD_SIZE THPs are currently
+ * supported. This will need to be updated to support other THP sizes.
+ *
+ * Returns the size of the mapping.
+ */
+static unsigned long
+transparent_hugepage_adjust(struct kvm_memory_slot *memslot,
+			    unsigned long hva, kvm_pfn_t *pfnp,
+			    phys_addr_t *ipap)
+{
+	kvm_pfn_t pfn = *pfnp;
+
+	/*
+	 * Make sure the adjustment is done only for THP pages. Also make
+	 * sure that the HVA and IPA are sufficiently aligned and that the
+	 * block map is contained within the memslot.
+	 */
+	if (kvm_is_transparent_hugepage(pfn) &&
+	    fault_supports_stage2_huge_mapping(memslot, hva, PMD_SIZE)) {
+		/*
+		 * The address we faulted on is backed by a transparent huge
+		 * page.  However, because we map the compound huge page and
+		 * not the individual tail page, we need to transfer the
+		 * refcount to the head page.  We have to be careful that the
+		 * THP doesn't start to split while we are adjusting the
+		 * refcounts.
+		 *
+		 * We are sure this doesn't happen, because mmu_notifier_retry
+		 * was successful and we are holding the mmu_lock, so if this
+		 * THP is trying to split, it will be blocked in the mmu
+		 * notifier before touching any of the pages, specifically
+		 * before being able to call __split_huge_page_refcount().
+		 *
+		 * We can therefore safely transfer the refcount from PG_tail
+		 * to PG_head and switch the pfn from a tail page to the head
+		 * page accordingly.
+		 */
+		*ipap &= PMD_MASK;
+		kvm_release_pfn_clean(pfn);
+		pfn &= ~(PTRS_PER_PMD - 1);
+		kvm_get_pfn(pfn);
+		*pfnp = pfn;
+
+		return PMD_SIZE;
+	}
+
+	/* Use page mapping if we cannot use block mapping. */
+	return PAGE_SIZE;
+}
+
 static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 			  struct kvm_memory_slot *memslot, unsigned long hva,
 			  unsigned long fault_status)
@@ -1773,20 +1785,13 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 	if (mmu_notifier_retry(kvm, mmu_seq))
 		goto out_unlock;
 
-	if (vma_pagesize == PAGE_SIZE && !force_pte) {
-		/*
-		 * Only PMD_SIZE transparent hugepages(THP) are
-		 * currently supported. This code will need to be
-		 * updated to support other THP sizes.
-		 *
-		 * Make sure the host VA and the guest IPA are sufficiently
-		 * aligned and that the block is contained within the memslot.
-		 */
-		if (fault_supports_stage2_huge_mapping(memslot, hva, PMD_SIZE) &&
-		    transparent_hugepage_adjust(&pfn, &fault_ipa))
-			vma_pagesize = PMD_SIZE;
-	}
-
+	/*
+	 * If we are not forced to use page mapping, check if we are
+	 * backed by a THP and thus use block mapping if possible.
+	 */
+	if (vma_pagesize == PAGE_SIZE && !force_pte)
+		vma_pagesize = transparent_hugepage_adjust(memslot, hva,
+							   &pfn, &fault_ipa);
 	if (writable)
 		kvm_set_pfn_dirty(pfn);
 
-- 
2.19.1