linux-kernel - [PATCH 2/6] arm64/fp: Don't corrupt FPMR when streaming mode changes

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Message-Id: <20241203-arm64-sme-reenable-v1-2-d853479d1b77@kernel.org>
Date: Tue, 03 Dec 2024 12:45:54 +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>
Subject: [PATCH 2/6] arm64/fp: Don't corrupt FPMR when streaming mode
 changes

When we enter or exit streaming more FPMR is reset to 0.  This means
that when restoring the floating point state from memory we need to
restore FPMR after we restore SVCR, otherwise if we are entering or
exiting streaming mode as part of loading the new state the value of
FPMR will be corrupted.

Fixes: 203f2b95a882 ("arm64/fpsimd: Support FEAT_FPMR")
Signed-off-by: Mark Brown <broonie@...nel.org>
---
 arch/arm64/kernel/fpsimd.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index eca0b6a2fc6fa25d8c850a5b9e109b4d58809f54..a3bb17c88942eba031d26e9f75ad46f37b6dc621 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -359,9 +359,6 @@ static void task_fpsimd_load(void)
 	WARN_ON(preemptible());
 	WARN_ON(test_thread_flag(TIF_KERNEL_FPSTATE));
 
-	if (system_supports_fpmr())
-		write_sysreg_s(current->thread.uw.fpmr, SYS_FPMR);
-
 	if (system_supports_sve() || system_supports_sme()) {
 		switch (current->thread.fp_type) {
 		case FP_STATE_FPSIMD:
@@ -413,6 +410,9 @@ static void task_fpsimd_load(void)
 			restore_ffr = system_supports_fa64();
 	}
 
+	if (system_supports_fpmr())
+		write_sysreg_s(current->thread.uw.fpmr, SYS_FPMR);
+
 	if (restore_sve_regs) {
 		WARN_ON_ONCE(current->thread.fp_type != FP_STATE_SVE);
 		sve_load_state(sve_pffr(&current->thread),

-- 
2.39.5