On Thu, 30 Sep 2021 19:11:30 +0100
Mark Brown <broonie@xxxxxxxxxx> wrote:
> By default all SME operations in userspace will trap. When this happens
> we allocate storage space for the SME register state, set up the SVE
> registers and disable traps. We do not need to initialize ZA since the
> architecture guarantees that it will be zeroed when enabled and when we
> trap ZA is disabled.
>
> On syscall we exit streaming mode if we were previously in it and ensure
> that all but the lower 128 bits of the registers are zeroed while
> preserving the state of ZA. This follows the aarch64 PCS for SME, ZA
> state is preserved over a function call and streaming mode is exited.
> Since the traps for SME do not distinguish between streaming mode SVE
> and ZA usage if ZA is in use rather than reenabling traps we instead
> zero the parts of the SVE registers not shared with FPSIMD and leave SME
> enabled, this simplifies handling SME traps. If ZA is not in use then we
> reenable SME traps and fall through to normal handling of SVE.
>
> Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
... continuing the trivial theme of my review today...
>
> /*
> * task_fpsimd_load() won't be called to update CPACR_EL1 in
> - * ret_to_user unless TIF_FOREIGN_FPSTATE is still set, which only
> - * happens if a context switch or kernel_neon_begin() or context
> - * modification (sigreturn, ptrace) intervenes.
> - * So, ensure that CPACR_EL1 is already correct for the fast-path case.
> + * ret_to_user unless TIF_FOREIGN_FPSTATE is still set, which
> + * only happens if a context switch or kernel_neon_begin() or
Why the rewrap here?
> + * context modification (sigreturn, ptrace) intervenes. So,
> + * ensure that CPACR_EL1 is already correct for the fast-path
> + * case.
> */
> sve_user_disable();
> }
>
> void do_el0_svc(struct pt_regs *regs)
> {
> - sve_user_discard();
> + fp_user_discard();
> el0_svc_common(regs, regs->regs[8], __NR_syscalls, sys_call_table);
> }
>
