[PATCH v2 1/6] arm64/sme: Flush foreign register state in do_sme_acc()

[Mark Brown]

When do_sme_acc() runs with foreign FP state it does not do any updates of
the task structure, relying on the next return to userspace to reload the
register state appropriately, but leaves the task's last loaded CPU
untouched. This means that if the task returns to userspace on the last
CPU it ran on then the checks in fpsimd_bind_task_to_cpu() will incorrectly
determine that the register state on the CPU is current and suppress reload
of the floating point register state before returning to userspace. This
will result in spurious warnings due to SME access traps occuring for the
task after TIF_SME is set.

Call fpsimd_flush_task_state() to invalidate the last loaded CPU
recorded in the task, forcing detection of the task as foreign.

Fixes: 8bd7f91c03d8 ("arm64/sme: Implement traps and syscall handling for SME")
Reported-by: Mark Rutlamd <mark.rutland at arm.com>
Signed-off-by: Mark Brown <broonie at kernel.org>
Cc: stable at vger.kernel.org
---
 arch/arm64/kernel/fpsimd.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index 8c4c1a2186cc510a7826d15ec36225857c07ed71..eca0b6a2fc6fa25d8c850a5b9e109b4d58809f54 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -1460,6 +1460,8 @@ void do_sme_acc(unsigned long esr, struct pt_regs *regs)
 		sme_set_vq(vq_minus_one);
 
 		fpsimd_bind_task_to_cpu();
+	} else {
+		fpsimd_flush_task_state(current);
 	}
 
 	put_cpu_fpsimd_context();

-- 
2.39.5