[PATCH 11/14] KVM: arm64: Restrict host updates to GITS_CTLR

Sebastian Ene
2026-03-10T12:50:17Z

Prevent unpredictable hardware behavior when the
host tries to enable the ITS while it is not in
quiescent state.

Signed-off-by: Sebastian Ene <sebastianene@google.com>
---
arch/arm64/kvm/hyp/nvhe/its_emulate.c | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)

diff --git a/arch/arm64/kvm/hyp/nvhe/its_emulate.c b/arch/arm64/kvm/hyp/nvhe/its_emulate.c
index 4782a9a24caa..539d2ee3b58e 100644
--- a/arch/arm64/kvm/hyp/nvhe/its_emulate.c
+++ b/arch/arm64/kvm/hyp/nvhe/its_emulate.c
@@ -274,6 +274,23 @@ static void cwriter_read(struct its_priv_state *its, u64 offset, u64 *read)
*read = readq_relaxed(its->base + GITS_CWRITER);
}

+static void ctlr_read(struct its_priv_state *its, u64 offset, u64 *read)
+{
+ *read = readq_relaxed(its->base + GITS_CTLR);
+}
+
+static void ctlr_write(struct its_priv_state *its, u64 offset, u64 value)
+{
+ u64 ctlr = readq_relaxed(its->base + GITS_CTLR);
+ bool is_quiescent = !!(ctlr & GITS_CTLR_QUIESCENT);
+ bool is_enabled = !!(ctlr & GITS_CTLR_ENABLE);
+
+ if (!is_enabled && (value & GITS_CTLR_ENABLE) && !is_quiescent)
+ return;
+
+ writeq_relaxed(value, its->base + GITS_CTLR);
+}
+
#define ITS_HANDLER(off, sz, write_cb, read_cb) \
{ \
.offset = (off), \
@@ -284,6 +301,7 @@ static void cwriter_read(struct its_priv_state *its, u64 offset, u64 *read)

static struct its_handler its_handlers[] = {
ITS_HANDLER(GITS_CWRITER, sizeof(u64), cwriter_write, cwriter_read),
+ ITS_HANDLER(GITS_CTLR, sizeof(u64), ctlr_write, ctlr_read),
{},
};

--
2.53.0.473.g4a7958ca14-goog