Re: [PATCH] kvm: arm: Enforce PTE mappings at stage2 when needed

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Hi Suzuki,

On 2019/3/12 17:52, Suzuki K Poulose wrote:
commit 6794ad5443a2118 ("KVM: arm/arm64: Fix unintended stage 2 PMD mappings")
made the checks to skip huge mappings, stricter. However it introduced
a bug where we still use huge mappings, ignoring the flag to
use PTE mappings, by not reseting the vma_pagesize to PAGE_SIZE.

Also, the checks do not cover the PUD huge pages, that was
under review during the same period. This patch fixes both
the issues.

Fixes : 6794ad5443a2118 ("KVM: arm/arm64: Fix unintended stage 2 PMD mappings")
Reported-by: Zenghui Yu <yuzenghui@xxxxxxxxxx>
Cc: Zenghui Yu <yuzenghui@xxxxxxxxxx>
Cc: Christoffer Dall <christoffer.dall@xxxxxxx>
Cc: Marc Zyngier <marc.zyngier@xxxxxxx>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
---

Thanks for Cc-ing me. It works fine now!


zenghui

  virt/kvm/arm/mmu.c | 43 +++++++++++++++++++++----------------------
  1 file changed, 21 insertions(+), 22 deletions(-)

diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
index 30251e2..66e0fbb5 100644
--- a/virt/kvm/arm/mmu.c
+++ b/virt/kvm/arm/mmu.c
@@ -1595,8 +1595,9 @@ static void kvm_send_hwpoison_signal(unsigned long address,
  	send_sig_mceerr(BUS_MCEERR_AR, (void __user *)address, lsb, current);
  }
-static bool fault_supports_stage2_pmd_mappings(struct kvm_memory_slot *memslot,
-					       unsigned long hva)
+static bool fault_supports_stage2_huge_mapping(struct kvm_memory_slot *memslot,
+					       unsigned long hva,
+					       unsigned long map_size)
  {
  	gpa_t gpa_start, gpa_end;
  	hva_t uaddr_start, uaddr_end;
@@ -1612,34 +1613,34 @@ static bool fault_supports_stage2_pmd_mappings(struct kvm_memory_slot *memslot,
/*
  	 * Pages belonging to memslots that don't have the same alignment
-	 * within a PMD for userspace and IPA cannot be mapped with stage-2
-	 * PMD entries, because we'll end up mapping the wrong pages.
+	 * within a PMD/PUD for userspace and IPA cannot be mapped with stage-2
+	 * PMD/PUD entries, because we'll end up mapping the wrong pages.
  	 *
  	 * Consider a layout like the following:
  	 *
  	 *    memslot->userspace_addr:
  	 *    +-----+--------------------+--------------------+---+
-	 *    |abcde|fgh  Stage-1 PMD    |    Stage-1 PMD   tv|xyz|
+	 *    |abcde|fgh  Stage-1 block  |    Stage-1 block tv|xyz|
  	 *    +-----+--------------------+--------------------+---+
  	 *
  	 *    memslot->base_gfn << PAGE_SIZE:
  	 *      +---+--------------------+--------------------+-----+
-	 *      |abc|def  Stage-2 PMD    |    Stage-2 PMD     |tvxyz|
+	 *      |abc|def  Stage-2 block  |    Stage-2 block   |tvxyz|
  	 *      +---+--------------------+--------------------+-----+
  	 *
-	 * If we create those stage-2 PMDs, we'll end up with this incorrect
+	 * If we create those stage-2 blocks, we'll end up with this incorrect
  	 * mapping:
  	 *   d -> f
  	 *   e -> g
  	 *   f -> h
  	 */
-	if ((gpa_start & ~S2_PMD_MASK) != (uaddr_start & ~S2_PMD_MASK))
+	if ((gpa_start & (map_size - 1)) != (uaddr_start & (map_size - 1)))
  		return false;
/*
  	 * Next, let's make sure we're not trying to map anything not covered
-	 * by the memslot. This means we have to prohibit PMD size mappings
-	 * for the beginning and end of a non-PMD aligned and non-PMD sized
+	 * by the memslot. This means we have to prohibit block size mappings
+	 * for the beginning and end of a non-block aligned and non-block sized
  	 * memory slot (illustrated by the head and tail parts of the
  	 * userspace view above containing pages 'abcde' and 'xyz',
  	 * respectively).
@@ -1648,8 +1649,8 @@ static bool fault_supports_stage2_pmd_mappings(struct kvm_memory_slot *memslot,
  	 * userspace_addr or the base_gfn, as both are equally aligned (per
  	 * the check above) and equally sized.
  	 */
-	return (hva & S2_PMD_MASK) >= uaddr_start &&
-	       (hva & S2_PMD_MASK) + S2_PMD_SIZE <= uaddr_end;
+	return (hva & ~(map_size - 1)) >= uaddr_start &&
+	       (hva & ~(map_size - 1)) + map_size <= uaddr_end;
  }
static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
@@ -1678,12 +1679,6 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
  		return -EFAULT;
  	}
- if (!fault_supports_stage2_pmd_mappings(memslot, hva))
-		force_pte = true;
-
-	if (logging_active)
-		force_pte = true;
-
  	/* Let's check if we will get back a huge page backed by hugetlbfs */
  	down_read(&current->mm->mmap_sem);
  	vma = find_vma_intersection(current->mm, hva, hva + 1);
@@ -1694,6 +1689,12 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
  	}
vma_pagesize = vma_kernel_pagesize(vma);
+	if (logging_active ||
+	    !fault_supports_stage2_huge_mapping(memslot, hva, vma_pagesize)) {
+		force_pte = true;
+		vma_pagesize = PAGE_SIZE;
+	}
+
  	/*
  	 * The stage2 has a minimum of 2 level table (For arm64 see
  	 * kvm_arm_setup_stage2()). Hence, we are guaranteed that we can
@@ -1701,11 +1702,9 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
  	 * As for PUD huge maps, we must make sure that we have at least
  	 * 3 levels, i.e, PMD is not folded.
  	 */
-	if ((vma_pagesize == PMD_SIZE ||
-	     (vma_pagesize == PUD_SIZE && kvm_stage2_has_pmd(kvm))) &&
-	    !force_pte) {
+	if (vma_pagesize == PMD_SIZE ||
+	    (vma_pagesize == PUD_SIZE && kvm_stage2_has_pmd(kvm)))
  		gfn = (fault_ipa & huge_page_mask(hstate_vma(vma))) >> PAGE_SHIFT;
-	}
  	up_read(&current->mm->mmap_sem);
/* We need minimum second+third level pages */


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