From: Mark Brown Date: Wed, 9 Apr 2025 16:40:03 +0000 (+0100) Subject: arm64/fpsimd: Don't corrupt FPMR when streaming mode changes X-Git-Tag: v6.16-rc1~133^2~1^2~29 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=e5fa85fce08b21ed41643cb7968bf66bbd0532e3;p=thirdparty%2Fkernel%2Flinux.git arm64/fpsimd: Don't corrupt FPMR when streaming mode changes When the effective value of PSTATE.SM is changed from 0 to 1 or from 1 to 0 by any method, an entry or exit to/from streaming SVE mode is performed, and hardware automatically resets a number of registers. As of ARM DDI 0487 L.a, this means: * All implemented bits of the SVE vector registers are set to zero. * All implemented bits of the SVE predicate registers are set to zero. * All implemented bits of FFR are set to zero, if FFR is implemented in the new mode. * FPSR is set to 0x0000_0000_0800_009f. * FPMR is set to 0, if FPMR is implemented. Currently task_fpsimd_load() restores FPMR before restoring SVCR (which is an accessor for PSTATE.{SM,ZA}), and so the restored value of FPMR may be clobbered if the restored value of PSTATE.SM happens to differ from the initial value of PSTATE.SM. Fix this by moving the restore of FPMR later. Note: this was originally posted as [1]. Fixes: 203f2b95a882 ("arm64/fpsimd: Support FEAT_FPMR") Signed-off-by: Mark Brown Link: https://lore.kernel.org/linux-arm-kernel/20241204-arm64-sme-reenable-v2-2-bae87728251d@kernel.org/ [ Rutland: rewrite commit message ] Signed-off-by: Mark Rutland Link: https://lore.kernel.org/r/20250409164010.3480271-7-mark.rutland@arm.com Signed-off-by: Catalin Marinas --- diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c index b4858d85292b4..b19736f354a71 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: @@ -411,6 +408,9 @@ 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(¤t->thread),