linux-kernel - [PATCH v4 12/21] KVM: arm64: Add helpers to tag shared pages in SW bits

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Message-Id: <20210809152448.1810400-13-qperret@google.com>
Date:   Mon,  9 Aug 2021 16:24:39 +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 12/21] KVM: arm64: Add helpers to tag shared pages in SW bits

We will soon start annotating shared pages in page-tables in nVHE
protected mode. Define all the states in which a page can be (owned,
shared and owned, shared and borrowed), and provide helpers allowing to
convert this into SW bits annotations using the matching prot
attributes.

Reviewed-by: Fuad Tabba <tabba@...gle.com>
Signed-off-by: Quentin Perret <qperret@...gle.com>
---
 arch/arm64/kvm/hyp/include/nvhe/mem_protect.h | 26 +++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
index 9c227d87c36d..87b1690c439f 100644
--- a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
@@ -12,6 +12,32 @@
 #include <asm/virt.h>
 #include <nvhe/spinlock.h>
 
+/*
+ * SW bits 0-1 are reserved to track the memory ownership state of each page:
+ *   00: The page is owned exclusively by the page-table owner.
+ *   01: The page is owned by the page-table owner, but is shared
+ *       with another entity.
+ *   10: The page is shared with, but not owned by the page-table owner.
+ *   11: Reserved for future use (lending).
+ */
+enum pkvm_page_state {
+	PKVM_PAGE_OWNED			= 0ULL,
+	PKVM_PAGE_SHARED_OWNED		= KVM_PGTABLE_PROT_SW0,
+	PKVM_PAGE_SHARED_BORROWED	= KVM_PGTABLE_PROT_SW1,
+};
+
+#define PKVM_PAGE_STATE_PROT_MASK	(KVM_PGTABLE_PROT_SW0 | KVM_PGTABLE_PROT_SW1)
+static inline enum kvm_pgtable_prot pkvm_mkstate(enum kvm_pgtable_prot prot,
+						 enum pkvm_page_state state)
+{
+	return (prot & ~PKVM_PAGE_STATE_PROT_MASK) | state;
+}
+
+static inline enum pkvm_page_state pkvm_getstate(enum kvm_pgtable_prot prot)
+{
+	return prot & PKVM_PAGE_STATE_PROT_MASK;
+}
+
 struct host_kvm {
 	struct kvm_arch arch;
 	struct kvm_pgtable pgt;
-- 
2.32.0.605.g8dce9f2422-goog