The THP code in KVM/ARM is a bit restrictive in not allowing a THP
to be used if the VMA is not 2MB aligned. Actually, it is not so much
the VMA that matters, but the associated memslot:
A process can perfectly mmap a region with no particular alignment
restriction, and then pass a 2MB aligned address to KVM. In this
case, KVM will only use this 2MB aligned region, and will ignore
the range between vma->vm_start and memslot->userspace_addr.
The fix is then to check the alignment of memslot->userspace_addr.
Cc: Christoffer Dall <christoffer.dall@xxxxxxxxxx>
Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
---
arch/arm/kvm/mmu.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
index 5809069..cec641a 100644
--- a/arch/arm/kvm/mmu.c
+++ b/arch/arm/kvm/mmu.c
@@ -667,14 +667,14 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
gfn = (fault_ipa & PMD_MASK) >> PAGE_SHIFT;
} else {
/*
- * Pages belonging to VMAs not aligned to the PMD mapping
+ * Pages belonging to memslots not aligned to the PMD mapping
* granularity cannot be mapped using block descriptors even
* if the pages belong to a THP for the process, because the
* stage-2 block descriptor will cover more than a single THP
* and we loose atomicity for unmapping, updates, and splits
* of the THP or other pages in the stage-2 block range.
*/
- if (vma->vm_start & ~PMD_MASK)
+ if (memslot->userspace_addr & ~PMD_MASK)
force_pte = true;
}
up_read(¤t->mm->mmap_sem);
--
1.8.2.3
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