linux-kernel - [PATCH v4 08/21] KVM: arm64: Don't overwrite software bits with owner id

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Message-Id: <20210809152448.1810400-9-qperret@google.com>
Date:   Mon,  9 Aug 2021 16:24:35 +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 08/21] KVM: arm64: Don't overwrite software bits with owner id

We will soon start annotating page-tables with new flags to track shared
pages and such, and we will do so in valid mappings using software bits
in the PTEs, as provided by the architecture. However, it is possible
that we will need to use those flags to annotate invalid mappings as
well in the future, similar to what we do to track page ownership in the
host stage-2.

In order to facilitate the annotation of invalid mappings with such
flags, it would be preferable to re-use the same bits as for valid
mappings (bits [58-55]), but these are currently used for ownership
encoding. Since we have plenty of bits left to use in invalid
mappings, move the ownership bits further down the PTE to avoid the
conflict.

Reviewed-by: Fuad Tabba <tabba@...gle.com>
Signed-off-by: Quentin Perret <qperret@...gle.com>
---
 arch/arm64/kvm/hyp/pgtable.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 59a394d82de3..1ee1168ac32d 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -46,7 +46,7 @@
 					 KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W | \
 					 KVM_PTE_LEAF_ATTR_HI_S2_XN)

-#define KVM_INVALID_PTE_OWNER_MASK	GENMASK(63, 56)
+#define KVM_INVALID_PTE_OWNER_MASK	GENMASK(9, 2)
 #define KVM_MAX_OWNER_ID		1

 struct kvm_pgtable_walk_data {
-- 
2.32.0.605.g8dce9f2422-goog