[RFC PATCH v2 4/4] arm64: realm: Move RSI detection earlier

[Suzuki K Poulose]

As discussed in [0], Realm world detection happens too late for making the
decision for the Linear map granularity for Arm64. If the boot CPU doesn't support
BBML2_NOABORT, it is difficult to break the mapping to PTE level. To solve this
try probing the Realm world earlier,  now that we probe the PSCI/SMCCC earlier.
Like the PSCI probe, if we fall back to the later point if the SMCCC probe
wasn't successful. We should probably add a WARNING/panic the system if the
BBML2_NOABORT is not supported on the boot CPU and linear map was created
with block mappings. This may case avoided by using rodata=full.

[0] https://lore.kernel.org/all/20260330161705.3349825-2-ryan.roberts@arm.com/

Signed-off-by: Suzuki K Poulose <suzuki.poulose at arm.com>
---
 arch/arm64/include/asm/rsi.h |  1 +
 arch/arm64/kernel/rsi.c      | 23 ++++++++++++++++++++++-
 arch/arm64/kernel/setup.c    |  3 ++-
 3 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/rsi.h b/arch/arm64/include/asm/rsi.h
index 88b50d660e85..4456bf0a1f23 100644
--- a/arch/arm64/include/asm/rsi.h
+++ b/arch/arm64/include/asm/rsi.h
@@ -14,6 +14,7 @@
 
 DECLARE_STATIC_KEY_FALSE(rsi_present);
 
+void __init arm64_early_rsi_init(void);
 void __init arm64_rsi_init(void);
 
 bool arm64_rsi_is_protected(phys_addr_t base, size_t size);
diff --git a/arch/arm64/kernel/rsi.c b/arch/arm64/kernel/rsi.c
index 92160f2e57ff..f0fd0922609d 100644
--- a/arch/arm64/kernel/rsi.c
+++ b/arch/arm64/kernel/rsi.c
@@ -139,10 +139,14 @@ static int realm_ioremap_hook(phys_addr_t phys, size_t size, pgprot_t *prot)
 	return 0;
 }
 
-void __init arm64_rsi_init(void)
+static bool rsi_probed = 0;
+
+static void __init rsi_probe(void)
 {
 	if (arm_smccc_1_1_get_conduit() != SMCCC_CONDUIT_SMC)
 		return;
+
+	rsi_probed = true;
 	if (!rsi_version_matches())
 		return;
 	if (WARN_ON(rsi_get_realm_config(lm_alias(&config))))
@@ -160,6 +164,23 @@ void __init arm64_rsi_init(void)
 	static_branch_enable(&rsi_present);
 }
 
+void __init arm64_early_rsi_init(void)
+{
+	rsi_probe();
+}
+
+void __init arm64_rsi_init(void)
+{
+	if (rsi_probed)
+		return;
+
+	rsi_probe();
+	/*
+	 * TODO: Warn if we don't have BBML2_NOABORT and page mapping is
+	 * not used.
+	 */
+}
+
 static struct platform_device rsi_dev = {
 	.name = RSI_PDEV_NAME,
 	.id = PLATFORM_DEVID_NONE
diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
index af35a0f3b7d0..0b530a090150 100644
--- a/arch/arm64/kernel/setup.c
+++ b/arch/arm64/kernel/setup.c
@@ -350,7 +350,8 @@ static void __init early_psci_init(void)
 		return;
 	}
 
-	psci_early_init_conduit(conduit);
+	if (!psci_early_init_conduit(conduit))
+		arm64_early_rsi_init();
 }
 
 void __init __no_sanitize_address setup_arch(char **cmdline_p)
-- 
2.43.0