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

On Fri, Jan 19, 2024 at 12:29:13PM +0000, Mark Brown wrote:

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@kernel.org Cc: stable@vger.kernel.org

---

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 1559c706d32d..80133c190136 100644 --- a/arch/arm64/kernel/fpsimd.c +++ b/arch/arm64/kernel/fpsimd.c @@ -1626,7 +1626,7 @@ 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);

}

I don't think this hunk applies on -rc2 ^^.

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());

I think this code is preemptible, so I'm struggling to understand what happens if the fp_type changes under our feet as a result of a context switch.

Will