[PATCH v2 3/6] arm64: hyperv: Add per-CPU RSI host call infrastructure for CCA Realms

[Kameron Carr <kameroncarr@linux.microsoft.com>]

Arm CCA Realms cannot issue Hyper-V hypercalls via HVC; the guest must
route them through the RSI_HOST_CALL interface, which takes the IPA of a
per-CPU rsi_host_call structure as its argument.

Add hv_hostcall_array as a per-CPU struct array and allocate it during
hyperv_init(). The allocation is gated on is_realm_world() so non-Realm
arm64 Hyper-V guests pay no memory cost.

Signed-off-by: Kameron Carr <kameroncarr@linux.microsoft.com>
---
 arch/arm64/hyperv/mshyperv.c      | 32 ++++++++++++++++++++++++++++++-
 arch/arm64/include/asm/mshyperv.h |  4 ++++
 2 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c
index 4fdc26ade1d74..7d536d7fb557e 100644
--- a/arch/arm64/hyperv/mshyperv.c
+++ b/arch/arm64/hyperv/mshyperv.c
@@ -15,10 +15,15 @@
 #include <linux/errno.h>
 #include <linux/version.h>
 #include <linux/cpuhotplug.h>
+#include <linux/slab.h>
 #include <asm/mshyperv.h>
+#include <asm/rsi.h>
 
 static bool hyperv_initialized;
 
+struct rsi_host_call *hv_hostcall_array;
+EXPORT_SYMBOL_GPL(hv_hostcall_array);
+
 int hv_get_hypervisor_version(union hv_hypervisor_version_info *info)
 {
 	hv_get_vpreg_128(HV_REGISTER_HYPERVISOR_VERSION,
@@ -60,6 +65,12 @@ static bool __init hyperv_detect_via_acpi(void)
 
 #endif
 
+static void hv_hostcall_free(void)
+{
+	kfree(hv_hostcall_array);
+	hv_hostcall_array = NULL;
+}
+
 static bool __init hyperv_detect_via_smccc(void)
 {
 	uuid_t hyperv_uuid = UUID_INIT(
@@ -85,6 +96,20 @@ static int __init hyperv_init(void)
 	if (!hyperv_detect_via_acpi() && !hyperv_detect_via_smccc())
 		return 0;
 
+	/*
+	 * The RSI host-call buffers are only ever used when
+	 * is_realm_world() is true. Skip the allocation on non-Realm
+	 * guests. A single contiguous array of nr_cpu_ids entries is
+	 * allocated; each CPU indexes into it by its processor ID.
+	 */
+	if (is_realm_world()) {
+		hv_hostcall_array = kcalloc(nr_cpu_ids,
+					    sizeof(struct rsi_host_call),
+					    GFP_KERNEL);
+		if (!hv_hostcall_array)
+			return -ENOMEM;
+	}
+
 	/* Setup the guest ID */
 	guest_id = hv_generate_guest_id(LINUX_VERSION_CODE);
 	hv_set_vpreg(HV_REGISTER_GUEST_OS_ID, guest_id);
@@ -106,12 +131,13 @@ static int __init hyperv_init(void)
 
 	ret = hv_common_init();
 	if (ret)
-		return ret;
+		goto free_hostcall_mem;
 
 	ret = cpuhp_setup_state(CPUHP_AP_HYPERV_ONLINE, "arm64/hyperv_init:online",
 				hv_common_cpu_init, hv_common_cpu_die);
 	if (ret < 0) {
 		hv_common_free();
+		hv_hostcall_free();
 		return ret;
 	}
 
@@ -125,6 +151,10 @@ static int __init hyperv_init(void)
 
 	hyperv_initialized = true;
 	return 0;
+
+free_hostcall_mem:
+	hv_hostcall_free();
+	return ret;
 }
 
 early_initcall(hyperv_init);
diff --git a/arch/arm64/include/asm/mshyperv.h b/arch/arm64/include/asm/mshyperv.h
index b721d3134ab66..c207a3f79b99b 100644
--- a/arch/arm64/include/asm/mshyperv.h
+++ b/arch/arm64/include/asm/mshyperv.h
@@ -63,4 +63,8 @@ static inline u64 hv_get_non_nested_msr(unsigned int reg)
 
 #include <asm-generic/mshyperv.h>
 
+/* Per-CPU-indexed RSI host call structures for CCA Realms */
+struct rsi_host_call;
+extern struct rsi_host_call *hv_hostcall_array;
+
 #endif
-- 
2.45.4