[PATCH v2] arm64/signal: Don't assume that TIF_SVE means we saved SVE state

[Mark Brown]

When we are in a syscall we will only save the FPSIMD subset even though
the task still has access to the full register set, and on context switch
we will only remove TIF_SVE when loading the register state. This means
that the signal handling code should not assume that TIF_SVE means that
the register state is stored in SVE format, it should instead check the
format that was recorded during save.

Fixes: 8c845e273104 ("arm64/sve: Leave SVE enabled on syscall if we don't context switch")
Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
Changes in v2:
- Rebase onto v6.8-rc2.
- Link to v1: https://lore.kernel.org/r/20240119-arm64-sve-signal-regs-v1-1-b9fd61b0289a@xxxxxxxxxx
---
 arch/arm64/kernel/fpsimd.c | 2 +-
 arch/arm64/kernel/signal.c | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index a5dc6f764195..25ceaee6b025 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -1635,7 +1635,7 @@ void fpsimd_preserve_current_state(void)
 void fpsimd_signal_preserve_current_state(void)
 {
 	fpsimd_preserve_current_state();
-	if (test_thread_flag(TIF_SVE))
+	if (current->thread.fp_type == FP_STATE_SVE)
 		sve_to_fpsimd(current);
 }
 
diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index 0e8beb3349ea..425b1bc17a3f 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -242,7 +242,7 @@ static int preserve_sve_context(struct sve_context __user *ctx)
 		vl = task_get_sme_vl(current);
 		vq = sve_vq_from_vl(vl);
 		flags |= SVE_SIG_FLAG_SM;
-	} else if (test_thread_flag(TIF_SVE)) {
+	} else if (current->thread.fp_type == FP_STATE_SVE) {
 		vq = sve_vq_from_vl(vl);
 	}
 
@@ -878,7 +878,7 @@ static int setup_sigframe_layout(struct rt_sigframe_user_layout *user,
 	if (system_supports_sve() || system_supports_sme()) {
 		unsigned int vq = 0;
 
-		if (add_all || test_thread_flag(TIF_SVE) ||
+		if (add_all || current->thread.fp_type == FP_STATE_SVE ||
 		    thread_sm_enabled(&current->thread)) {
 			int vl = max(sve_max_vl(), sme_max_vl());
 

---
base-commit: 41bccc98fb7931d63d03f326a746ac4d429c1dd3
change-id: 20240118-arm64-sve-signal-regs-5711e0d10425

Best regards,
-- 
Mark Brown <broonie@xxxxxxxxxx>