commit 82e0191a1aa11abfddb22c8944989b7735560efc
author Suzuki K Poulose <suzuki.poulose@arm.com> Tue Nov 08 13:56:21 2016 +0000
committer Catalin Marinas <catalin.marinas@arm.com> Wed Nov 16 18:05:10 2016 +0000
tree 192b21e7191e2385dc4a58f0562fff4a2f5f68b4
parent a4023f682739439b434165b54af7cb3676a4766e

arm64: Support systems without FP/ASIMD

The arm64 kernel assumes that FP/ASIMD units are always present
and accesses the FP/ASIMD specific registers unconditionally. This
could cause problems when they are absent. This patch adds the
support for kernel handling systems without FP/ASIMD by skipping the
register access within the kernel. For kvm, we trap the accesses
to FP/ASIMD and inject an undefined instruction exception to the VM.

The callers of the exported kernel_neon_begin_partial() should
make sure that the FP/ASIMD is supported.

Cc: Will Deacon <will.deacon@arm.com>
Cc: Christoffer Dall <christoffer.dall@linaro.org>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
[catalin.marinas@arm.com: add comment on the ARM64_HAS_NO_FPSIMD conflict and the new location]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/kernel/fpsimd.c

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index 394c61d..b883f1f 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -127,6 +127,8 @@ void do_fpsimd_exc(unsigned int esr, struct pt_regs *regs)
 
 void fpsimd_thread_switch(struct task_struct *next)
 {
+	if (!system_supports_fpsimd())
+		return;
 	/*
 	 * Save the current FPSIMD state to memory, but only if whatever is in
 	 * the registers is in fact the most recent userland FPSIMD state of
@@ -157,6 +159,8 @@ void fpsimd_thread_switch(struct task_struct *next)
 
 void fpsimd_flush_thread(void)
 {
+	if (!system_supports_fpsimd())
+		return;
 	memset(&current->thread.fpsimd_state, 0, sizeof(struct fpsimd_state));
 	fpsimd_flush_task_state(current);
 	set_thread_flag(TIF_FOREIGN_FPSTATE);
@@ -168,6 +172,8 @@ void fpsimd_flush_thread(void)
  */
 void fpsimd_preserve_current_state(void)
 {
+	if (!system_supports_fpsimd())
+		return;
 	preempt_disable();
 	if (!test_thread_flag(TIF_FOREIGN_FPSTATE))
 		fpsimd_save_state(&current->thread.fpsimd_state);
@@ -181,6 +187,8 @@ void fpsimd_preserve_current_state(void)
  */
 void fpsimd_restore_current_state(void)
 {
+	if (!system_supports_fpsimd())
+		return;
 	preempt_disable();
 	if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) {
 		struct fpsimd_state *st = &current->thread.fpsimd_state;
@@ -199,6 +207,8 @@ void fpsimd_restore_current_state(void)
  */
 void fpsimd_update_current_state(struct fpsimd_state *state)
 {
+	if (!system_supports_fpsimd())
+		return;
 	preempt_disable();
 	fpsimd_load_state(state);
 	if (test_and_clear_thread_flag(TIF_FOREIGN_FPSTATE)) {
@@ -228,6 +238,8 @@ static DEFINE_PER_CPU(struct fpsimd_partial_state, softirq_fpsimdstate);
  */
 void kernel_neon_begin_partial(u32 num_regs)
 {
+	if (WARN_ON(!system_supports_fpsimd()))
+		return;
 	if (in_interrupt()) {
 		struct fpsimd_partial_state *s = this_cpu_ptr(
 			in_irq() ? &hardirq_fpsimdstate : &softirq_fpsimdstate);
@@ -252,6 +264,8 @@ EXPORT_SYMBOL(kernel_neon_begin_partial);
 
 void kernel_neon_end(void)
 {
+	if (!system_supports_fpsimd())
+		return;
 	if (in_interrupt()) {
 		struct fpsimd_partial_state *s = this_cpu_ptr(
 			in_irq() ? &hardirq_fpsimdstate : &softirq_fpsimdstate);