[PATCH v11 06/12] KVM: arm64: Allow userspace to change ID_AA64ISAR{0-2}_EL1

[Oliver Upton <oliver.upton@linux.dev>]

Almost all of the features described by the ISA registers have no KVM
involvement. Allow userspace to change the value of these registers with
a couple exceptions:

 - MOPS is not writable as KVM does not currently virtualize FEAT_MOPS.

 - The PAuth fields are not writable as KVM requires both address and
   generic authentication be enabled.

Co-developed-by: Jing Zhang <jingzhangos@google.com>
Signed-off-by: Jing Zhang <jingzhangos@google.com>
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
---
 arch/arm64/kvm/sys_regs.c | 38 ++++++++++++++++++++++++++------------
 1 file changed, 26 insertions(+), 12 deletions(-)

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index b342c96e08f4..09be55338e0a 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1851,11 +1851,14 @@ static unsigned int elx2_visibility(const struct kvm_vcpu *vcpu,
  * from userspace.
  */
 
-/* sys_reg_desc initialiser for known cpufeature ID registers */
-#define ID_SANITISED(name) {			\
+#define ID_DESC(name)				\
 	SYS_DESC(SYS_##name),			\
 	.access	= access_id_reg,		\
-	.get_user = get_id_reg,			\
+	.get_user = get_id_reg			\
+
+/* sys_reg_desc initialiser for known cpufeature ID registers */
+#define ID_SANITISED(name) {			\
+	ID_DESC(name),				\
 	.set_user = set_id_reg,			\
 	.visibility = id_visibility,		\
 	.reset = kvm_read_sanitised_id_reg,	\
@@ -1864,15 +1867,22 @@ static unsigned int elx2_visibility(const struct kvm_vcpu *vcpu,
 
 /* sys_reg_desc initialiser for known cpufeature ID registers */
 #define AA32_ID_SANITISED(name) {		\
-	SYS_DESC(SYS_##name),			\
-	.access	= access_id_reg,		\
-	.get_user = get_id_reg,			\
+	ID_DESC(name),				\
 	.set_user = set_id_reg,			\
 	.visibility = aa32_id_visibility,	\
 	.reset = kvm_read_sanitised_id_reg,	\
 	.val = 0,				\
 }
 
+/* sys_reg_desc initialiser for writable ID registers */
+#define ID_WRITABLE(name, mask) {		\
+	ID_DESC(name),				\
+	.set_user = set_id_reg,			\
+	.visibility = id_visibility,		\
+	.reset = kvm_read_sanitised_id_reg,	\
+	.val = mask,				\
+}
+
 /*
  * sys_reg_desc initialiser for architecturally unallocated cpufeature ID
  * register with encoding Op0=3, Op1=0, CRn=0, CRm=crm, Op2=op2
@@ -1894,9 +1904,7 @@ static unsigned int elx2_visibility(const struct kvm_vcpu *vcpu,
  * RAZ for the guest.
  */
 #define ID_HIDDEN(name) {			\
-	SYS_DESC(SYS_##name),			\
-	.access = access_id_reg,		\
-	.get_user = get_id_reg,			\
+	ID_DESC(name),				\
 	.set_user = set_id_reg,			\
 	.visibility = raz_visibility,		\
 	.reset = kvm_read_sanitised_id_reg,	\
@@ -2075,9 +2083,15 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 	ID_UNALLOCATED(5,7),
 
 	/* CRm=6 */
-	ID_SANITISED(ID_AA64ISAR0_EL1),
-	ID_SANITISED(ID_AA64ISAR1_EL1),
-	ID_SANITISED(ID_AA64ISAR2_EL1),
+	ID_WRITABLE(ID_AA64ISAR0_EL1, ~ID_AA64ISAR0_EL1_RES0),
+	ID_WRITABLE(ID_AA64ISAR1_EL1, ~(ID_AA64ISAR1_EL1_GPI |
+					ID_AA64ISAR1_EL1_GPA |
+					ID_AA64ISAR1_EL1_API |
+					ID_AA64ISAR1_EL1_APA)),
+	ID_WRITABLE(ID_AA64ISAR2_EL1, ~(ID_AA64ISAR2_EL1_RES0 |
+					ID_AA64ISAR2_EL1_MOPS |
+					ID_AA64ISAR2_EL1_APA3 |
+					ID_AA64ISAR2_EL1_GPA3)),
 	ID_UNALLOCATED(6,3),
 	ID_UNALLOCATED(6,4),
 	ID_UNALLOCATED(6,5),
-- 
2.42.0.609.gbb76f46606-goog