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

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Message-Id: <20201025230626.18501-1-gshan@redhat.com>
Date:   Mon, 26 Oct 2020 10:06:26 +1100
From:   Gavin Shan <gshan@...hat.com>
To:     kvmarm@...ts.cs.columbia.edu
Cc:     linux-kernel@...r.kernel.org, will@...nel.org,
        alexandru.elisei@....com, shan.gavin@...il.com
Subject: [PATCH v2] KVM: arm64: Failback on unsupported huge page sizes

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@...nel.org>
Signed-off-by: Gavin Shan <gshan@...hat.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