linux-kernel - [PATCH v2] arm64/fpsimd: Exit streaming mode when flushing tasks

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Message-Id: <20230607-arm64-flush-svcr-v2-1-827306001841@kernel.org>
Date:   Fri, 09 Jun 2023 23:43:41 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Anders Roxell <anders.roxell@...aro.org>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        Mark Brown <broonie@...nel.org>
Subject: [PATCH v2] arm64/fpsimd: Exit streaming mode when flushing tasks

Ensure there is no path where we might attempt to save SME state after we
flush a task by updating the SVCR register state as well as updating our
in memory state. I haven't seen a specific case where this is happening or
seen a path where it might happen but for the cost of a single low overhead
instruction it seems sensible to close the potential gap.

Signed-off-by: Mark Brown <broonie@...nel.org>
---
Changes in v2:
- Do a full SMSTOP to cover ZA as well.
- Link to v1: https://lore.kernel.org/r/20230607-arm64-flush-svcr-v1-1-7821a6199e0a@kernel.org
---
 arch/arm64/kernel/fpsimd.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index 2fbafa5cc7ac..7a1aeb95d7c3 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -1649,6 +1649,7 @@ void fpsimd_flush_thread(void)
 
 		fpsimd_flush_thread_vl(ARM64_VEC_SME);
 		current->thread.svcr = 0;
+		sme_smstop();
 	}
 
 	current->thread.fp_type = FP_STATE_FPSIMD;

---
base-commit: 44c026a73be8038f03dbdeef028b642880cf1511
change-id: 20230607-arm64-flush-svcr-47cc76a8cbbc

Best regards,
-- 
Mark Brown <broonie@...nel.org>