[RFC PATCH 4/6] Drivers: hv: Mark shared memory as decrypted for CCA Realms

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

In hv_common_cpu_init(), the per-CPU hypercall input/output pages need
to be marked as decrypted (shared) for confidential VM isolation types.
This is already done for SNP and TDX isolation; extend the same handling
to Arm CCA Realm guests so that the host hypervisor can access the
shared hypercall buffers.

is_realm_world() is only declared in arch/arm64/include/asm/rsi.h, so
using it directly in the arch-neutral drivers/hv/hv_common.c would
break the x86 build. Introduce a Hyper-V-specific helper following the
established hv_isolation_type_snp() / hv_isolation_type_tdx() pattern.

On architectures other than arm64 the weak default keeps the existing
behaviour.

Signed-off-by: Kameron Carr <kameroncarr@linux.microsoft.com>
---
 arch/arm64/hyperv/mshyperv.c   | 5 +++++
 drivers/hv/hv_common.c         | 9 ++++++++-
 include/asm-generic/mshyperv.h | 1 +
 3 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c
index 08fec82691683..b595b2b9bdbbb 100644
--- a/arch/arm64/hyperv/mshyperv.c
+++ b/arch/arm64/hyperv/mshyperv.c
@@ -208,3 +208,8 @@ bool hv_is_hyperv_initialized(void)
 	return hyperv_initialized;
 }
 EXPORT_SYMBOL_GPL(hv_is_hyperv_initialized);
+
+bool hv_isolation_type_cca(void)
+{
+	return is_realm_world();
+}
diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c
index 6b67ac6167891..010c7d98b5de1 100644
--- a/drivers/hv/hv_common.c
+++ b/drivers/hv/hv_common.c
@@ -499,7 +499,8 @@ int hv_common_cpu_init(unsigned int cpu)
 		}
 
 		if (!ms_hyperv.paravisor_present &&
-		    (hv_isolation_type_snp() || hv_isolation_type_tdx())) {
+		    (hv_isolation_type_snp() || hv_isolation_type_tdx() ||
+		     hv_isolation_type_cca())) {
 			ret = set_memory_decrypted((unsigned long)mem, pgcount);
 			if (ret) {
 				/* It may be unsafe to free 'mem' */
@@ -666,6 +667,12 @@ bool __weak hv_isolation_type_tdx(void)
 }
 EXPORT_SYMBOL_GPL(hv_isolation_type_tdx);
 
+bool __weak hv_isolation_type_cca(void)
+{
+	return false;
+}
+EXPORT_SYMBOL_GPL(hv_isolation_type_cca);
+
 void __weak hv_setup_vmbus_handler(void (*handler)(void))
 {
 }
diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
index bf601d67cecb9..1fa79abce743c 100644
--- a/include/asm-generic/mshyperv.h
+++ b/include/asm-generic/mshyperv.h
@@ -79,6 +79,7 @@ u64 hv_do_fast_hypercall16(u16 control, u64 input1, u64 input2);
 
 bool hv_isolation_type_snp(void);
 bool hv_isolation_type_tdx(void);
+bool hv_isolation_type_cca(void);
 
 /*
  * On architectures where Hyper-V doesn't support AEOI (e.g., ARM64),
-- 
2.45.4