linux-kernel - [PATCH v4 09/21] KVM: arm64: Tolerate re-creating hyp mappings to set software bits

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Message-Id: <20210809152448.1810400-10-qperret@google.com>
Date:   Mon,  9 Aug 2021 16:24:36 +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,
        qperret@...gle.com
Subject: [PATCH v4 09/21] KVM: arm64: Tolerate re-creating hyp mappings to set
 software 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 software bits, as that will soon be needed to annotate shared
pages.

Reviewed-by: Fuad Tabba <tabba@...gle.com>
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 1ee1168ac32d..2689fcb7901d 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -362,6 +362,21 @@ 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)
+{
+	/*
+	 * Tolerate KVM recreating the exact same mapping, or changing software
+	 * bits if the existing mapping was valid.
+	 */
+	if (old == new)
+		return false;
+
+	if (!kvm_pte_valid(old))
+		return true;
+
+	return !WARN_ON((old ^ new) & ~KVM_PTE_LEAF_ATTR_HI_SW);
+}
+
 static bool hyp_map_walker_try_leaf(u64 addr, u64 end, u32 level,
 				    kvm_pte_t *ptep, struct hyp_map_data *data)
 {
@@ -371,9 +386,8 @@ 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 */
 	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;
-- 
2.32.0.605.g8dce9f2422-goog