[PATCH v1 20/38] arm64/sme: Implement support for TPIDR2

[Mark Brown]

The Scalable Matrix Extension introduces support for a new thread specific
data register TPIDR2 intended for use by libc. The kernel must save the
value of TPIDR2 on context switch and should ensure that all new threads
start off with a default value of 0. Add a field to the thread_struct to
store TPIDR2 and context switch it with the other thread specific data.

In case there are future extensions which also use TPIDR2 we introduce
system_supports_tpidr2() and use that rather than system_supports_sme()
for TPIDR2 handling.

Signed-off-by: Mark Brown <broonie at kernel.org>
---
 arch/arm64/include/asm/cpufeature.h | 5 +++++
 arch/arm64/include/asm/processor.h  | 1 +
 arch/arm64/kernel/fpsimd.c          | 4 ++++
 arch/arm64/kernel/process.c         | 5 +++++
 4 files changed, 15 insertions(+)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 9a183267b341..8d0cff410b40 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -740,6 +740,11 @@ static __always_inline bool system_supports_sme(void)
 		cpus_have_const_cap(ARM64_SME);
 }
 
+static __always_inline bool system_supports_tpidr2(void)
+{
+	return system_supports_sme();
+}
+
 static __always_inline bool system_supports_cnp(void)
 {
 	return IS_ENABLED(CONFIG_ARM64_CNP) &&
diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index a62d2f8045bf..51eca2513cb5 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -168,6 +168,7 @@ struct thread_struct {
 	u64			mte_ctrl;
 #endif
 	u64			sctlr_user;
+	u64			tpidr2_el0;
 };
 
 static inline unsigned int thread_get_vl(struct thread_struct *thread,
diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index 9511428c2e81..e673a1d6a618 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -1099,6 +1099,10 @@ void sme_kernel_enable(const struct arm64_cpu_capabilities *__always_unused p)
 	/* Allow SME in kernel */
 	write_sysreg(read_sysreg(CPACR_EL1) | CPACR_EL1_SMEN_EL1EN, CPACR_EL1);
 	isb();
+
+	/* Allow EL0 to access TPIDR2 */
+	write_sysreg(read_sysreg(SCTLR_EL1) | SCTLR_ELx_ENTP2, SCTLR_EL1);
+	isb();
 }
 
 /*
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 40adb8cdbf5a..0640b51d4289 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -377,6 +377,7 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start,
 	 * as the final frame for the new task.
 	 */
 	p->thread.cpu_context.fp = (unsigned long)childregs->stackframe;
+	p->thread.tpidr2_el0 = 0;
 
 	ptrace_hw_copy_thread(p);
 
@@ -386,6 +387,8 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start,
 void tls_preserve_current_state(void)
 {
 	*task_user_tls(current) = read_sysreg(tpidr_el0);
+	if (system_supports_tpidr2())
+		current->thread.tpidr2_el0 = read_sysreg_s(SYS_TPIDR2_EL0);
 }
 
 static void tls_thread_switch(struct task_struct *next)
@@ -398,6 +401,8 @@ static void tls_thread_switch(struct task_struct *next)
 		write_sysreg(0, tpidrro_el0);
 
 	write_sysreg(*task_user_tls(next), tpidr_el0);
+	if (system_supports_tpidr2())
+		write_sysreg_s(next->thread.tpidr2_el0, SYS_TPIDR2_EL0);
 }
 
 /*
-- 
2.20.1