[PATCH v2] KVM: arm64: Failback on unsupported huge page sizes

[PATCH v2] KVM: arm64: Failback on unsupported huge page sizes

[Gavin Shan]

The huge page could be mapped through multiple contiguous PMDs or PTEs.
The corresponding huge page sizes aren't supported by the page table
walker currently.

This fails the unsupported huge page sizes to the near one. Otherwise,
the guest can't boot successfully: CONT_PMD_SHIFT and CONT_PTE_SHIFT
fail back to PMD_SHIFT and PAGE_SHIFT separately.

Suggested-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Gavin Shan <gshan@redhat.com>
---
v2: Reorganize the code as Marc suggested
---
 arch/arm64/kvm/mmu.c | 26 +++++++++++++++++++-------
 1 file changed, 19 insertions(+), 7 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index a816cb8e619b..e431d2d8e368 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -787,14 +787,26 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 		vma_shift = PAGE_SHIFT;
 	}
 
-	if (vma_shift == PUD_SHIFT &&
-	    !fault_supports_stage2_huge_mapping(memslot, hva, PUD_SIZE))
-	       vma_shift = PMD_SHIFT;
-
-	if (vma_shift == PMD_SHIFT &&
-	    !fault_supports_stage2_huge_mapping(memslot, hva, PMD_SIZE)) {
-		force_pte = true;
+	switch (vma_shift) {
+	case PUD_SHIFT:
+		if (fault_supports_stage2_huge_mapping(memslot, hva, PUD_SIZE))
+			break;
+		fallthrough;
+	case CONT_PMD_SHIFT:
+		vma_shift = PMD_SHIFT;
+		fallthrough;
+	case PMD_SHIFT:
+		if (fault_supports_stage2_huge_mapping(memslot, hva, PMD_SIZE))
+			break;
+		fallthrough;
+	case CONT_PTE_SHIFT:
 		vma_shift = PAGE_SHIFT;
+		force_pte = true;
+		fallthrough;
+	case PAGE_SHIFT:
+		break;
+	default:
+		WARN_ONCE(1, "Unknown vma_shift %d", vma_shift);
 	}
 
 	vma_pagesize = 1UL << vma_shift;
-- 
2.23.0

Re: [PATCH v2] KVM: arm64: Failback on unsupported huge page sizes

[Marc Zyngier]

On Mon, 26 Oct 2020 10:06:26 +1100, Gavin Shan wrote:
> The huge page could be mapped through multiple contiguous PMDs or PTEs.
> The corresponding huge page sizes aren't supported by the page table
> walker currently.
> 
> This fails the unsupported huge page sizes to the near one. Otherwise,
> the guest can't boot successfully: CONT_PMD_SHIFT and CONT_PTE_SHIFT
> fail back to PMD_SHIFT and PAGE_SHIFT separately.

Applied to next, thanks!

[1/1] KVM: arm64: Use fallback mapping sizes for contiguous huge page sizes
      commit: 2f40c46021bbb3ecd5c5f05764ecccbc276bc690

Cheers,

	M.
-- 
Without deviation from the norm, progress is not possible.