linux-kernel - [PATCH 2/2] arm64/sme: Flush foreign register state in do_sme

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Message-Id: <20241030-arm64-fpsimd-foreign-flush-v1-2-bd7bd66905a2@kernel.org>
Date: Wed, 30 Oct 2024 20:23:51 +0000
From: Mark Brown <broonie@...nel.org>
To: Catalin Marinas <catalin.marinas@....com>, 
 Will Deacon <will@...nel.org>
Cc: Mark Rutland <mark.rutland@....com>, 
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
 Mark Brown <broonie@...nel.org>, stable@...r.kernel.org
Subject: [PATCH 2/2] arm64/sme: Flush foreign register state in
 do_sme_acc()

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@....com>
Signed-off-by: Mark Brown <broonie@...nel.org>
Cc: stable@...r.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 6d21971ae5594f32947480cfa168db400a69a283..1eaa670cbffa448c1aced8c8b37040492e18a21f 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();

-- 
2.39.2