KVM: arm64: Allow guest to set the OSLK bit

Allow writes to OSLAR and forward the OSLK bit to OSLSR. Do nothing with
the value for now.
Reviewed-by: NReiji Watanabe <reijiw@google.com>
Signed-off-by: NOliver Upton <oupton@google.com>
Signed-off-by: NMarc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220203174159.2887882-4-oupton@google.com

arch/arm64/include/asm/sysreg.h

@@ -128,12 +128,15 @@
 #define SYS_DBGWVRn_EL1(n)		sys_reg(2, 0, 0, n, 6)
 #define SYS_DBGWCRn_EL1(n)		sys_reg(2, 0, 0, n, 7)
 #define SYS_MDRAR_EL1			sys_reg(2, 0, 1, 0, 0)
+
 #define SYS_OSLAR_EL1			sys_reg(2, 0, 1, 0, 4)
+#define SYS_OSLAR_OSLK			BIT(0)
 
 #define SYS_OSLSR_EL1			sys_reg(2, 0, 1, 1, 4)
 #define SYS_OSLSR_OSLM_MASK		(BIT(3) | BIT(0))
 #define SYS_OSLSR_OSLM_NI		0
 #define SYS_OSLSR_OSLM_IMPLEMENTED	BIT(3)
+#define SYS_OSLSR_OSLK			BIT(1)
 
 #define SYS_OSDLR_EL1			sys_reg(2, 0, 1, 3, 4)
 #define SYS_DBGPRCR_EL1			sys_reg(2, 0, 1, 4, 4)

arch/arm64/kvm/sys_regs.c

@@ -44,6 +44,10 @@
  * 64bit interface.
  */
 
+static int reg_from_user(u64 *val, const void __user *uaddr, u64 id);
+static int reg_to_user(void __user *uaddr, const u64 *val, u64 id);
+static u64 sys_reg_to_index(const struct sys_reg_desc *reg);
+
 static bool read_from_write_only(struct kvm_vcpu *vcpu,
 				 struct sys_reg_params *params,
 				 const struct sys_reg_desc *r)
@@ -287,6 +291,24 @@ static bool trap_loregion(struct kvm_vcpu *vcpu,
 	return trap_raz_wi(vcpu, p, r);
 }
 
+static bool trap_oslar_el1(struct kvm_vcpu *vcpu,
+			   struct sys_reg_params *p,
+			   const struct sys_reg_desc *r)
+{
+	u64 oslsr;
+
+	if (!p->is_write)
+		return read_from_write_only(vcpu, p, r);
+
+	/* Forward the OSLK bit to OSLSR */
+	oslsr = __vcpu_sys_reg(vcpu, OSLSR_EL1) & ~SYS_OSLSR_OSLK;
+	if (p->regval & SYS_OSLAR_OSLK)
+		oslsr |= SYS_OSLSR_OSLK;
+
+	__vcpu_sys_reg(vcpu, OSLSR_EL1) = oslsr;
+	return true;
+}
+
 static bool trap_oslsr_el1(struct kvm_vcpu *vcpu,
 			   struct sys_reg_params *p,
 			   const struct sys_reg_desc *r)
@@ -309,9 +331,14 @@ static int set_oslsr_el1(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd,
 	if (err)
 		return err;
 
-	if (val != rd->val)
+	/*
+	 * The only modifiable bit is the OSLK bit. Refuse the write if
+	 * userspace attempts to change any other bit in the register.
+	 */
+	if ((val ^ rd->val) & ~SYS_OSLSR_OSLK)
 		return -EINVAL;
 
+	__vcpu_sys_reg(vcpu, rd->reg) = val;
 	return 0;
 }
 
@@ -1180,10 +1207,6 @@ static bool access_raz_id_reg(struct kvm_vcpu *vcpu,
 	return __access_id_reg(vcpu, p, r, true);
 }
 
-static int reg_from_user(u64 *val, const void __user *uaddr, u64 id);
-static int reg_to_user(void __user *uaddr, const u64 *val, u64 id);
-static u64 sys_reg_to_index(const struct sys_reg_desc *reg);
-
 /* Visibility overrides for SVE-specific control registers */
 static unsigned int sve_visibility(const struct kvm_vcpu *vcpu,
 				   const struct sys_reg_desc *rd)
@@ -1463,7 +1486,7 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 	DBG_BCR_BVR_WCR_WVR_EL1(15),
 
 	{ SYS_DESC(SYS_MDRAR_EL1), trap_raz_wi },
-	{ SYS_DESC(SYS_OSLAR_EL1), trap_raz_wi },
+	{ SYS_DESC(SYS_OSLAR_EL1), trap_oslar_el1 },
 	{ SYS_DESC(SYS_OSLSR_EL1), trap_oslsr_el1, reset_val, OSLSR_EL1,
 		SYS_OSLSR_OSLM_IMPLEMENTED, .set_user = set_oslsr_el1, },
 	{ SYS_DESC(SYS_OSDLR_EL1), trap_raz_wi },
@@ -1937,7 +1960,7 @@ static const struct sys_reg_desc cp14_regs[] = {
 
 	DBGBXVR(0),
 	/* DBGOSLAR */
-	{ Op1( 0), CRn( 1), CRm( 0), Op2( 4), trap_raz_wi },
+	{ Op1( 0), CRn( 1), CRm( 0), Op2( 4), trap_oslar_el1 },
 	DBGBXVR(1),
 	/* DBGOSLSR */
 	{ Op1( 0), CRn( 1), CRm( 1), Op2( 4), trap_oslsr_el1, NULL, OSLSR_EL1 },