linux-kernel - [PATCH 06/14] KVM: arm64: Tolerate re-creating hyp mappings to set ignored bits

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Message-Id: <20210719104735.3681732-7-qperret@google.com>
Date:   Mon, 19 Jul 2021 11:47:27 +0100
From:   Quentin Perret <qperret@...gle.com>
To:     maz@...nel.org, james.morse@....com, alexandru.elisei@....com,
        suzuki.poulose@....com, catalin.marinas@....com, will@...nel.org
Cc:     linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org, ardb@...nel.org, qwandor@...gle.com,
        tabba@...gle.com, dbrazdil@...gle.com, kernel-team@...roid.com,
        Quentin Perret <qperret@...gle.com>
Subject: [PATCH 06/14] KVM: arm64: Tolerate re-creating hyp mappings to set
 ignored bits

The current hypervisor stage-1 mapping code doesn't allow changing an
existing valid mapping. Relax this condition by allowing changes that
only target ignored bits, as that will soon be needed to annotate shared
pages.

Signed-off-by: Quentin Perret <qperret@...gle.com>
---
 arch/arm64/kvm/hyp/pgtable.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index a0ac8c2bc174..34cf67997a82 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -362,6 +362,17 @@ static int hyp_set_prot_attr(enum kvm_pgtable_prot prot, kvm_pte_t *ptep)
 	return 0;
 }
 
+static bool hyp_pte_needs_update(kvm_pte_t old, kvm_pte_t new)
+{
+	if (old == new)
+		return false;
+
+	if (!kvm_pte_valid(old))
+		return true;
+
+	return !WARN_ON((old ^ new) & ~KVM_PTE_LEAF_ATTR_IGNORED);
+}
+
 static bool hyp_map_walker_try_leaf(u64 addr, u64 end, u32 level,
 				    kvm_pte_t *ptep, struct hyp_map_data *data)
 {
@@ -371,9 +382,12 @@ static bool hyp_map_walker_try_leaf(u64 addr, u64 end, u32 level,
 	if (!kvm_block_mapping_supported(addr, end, phys, level))
 		return false;
 
-	/* Tolerate KVM recreating the exact same mapping */
+	/*
+	 * Tolerate KVM recreating the exact same mapping, or changing ignored
+	 * bits.
+	 */
 	new = kvm_init_valid_leaf_pte(phys, data->attr, level);
-	if (old != new && !WARN_ON(kvm_pte_valid(old)))
+	if (hyp_pte_needs_update(old, new))
 		smp_store_release(ptep, new);
 
 	data->phys += granule;
-- 
2.32.0.402.g57bb445576-goog