[PATCH v4 13/28] arm64/sve: Signal handling support

[Catalin Marinas]

On Fri, Oct 27, 2017 at 11:50:55AM +0100, Dave P Martin wrote:
> This patch implements support for saving and restoring the SVE
> registers around signals.
> 
> A fixed-size header struct sve_context is always included in the
> signal frame encoding the thread's vector length at the time of
> signal delivery, optionally followed by a variable-layout structure
> encoding the SVE registers.
> 
> Because of the need to preserve backwards compatibility, the FPSIMD
> view of the SVE registers is always dumped as a struct
> fpsimd_context in the usual way, in addition to any sve_context.
> 
> The SVE vector registers are dumped in full, including bits 127:0
> of each register which alias the corresponding FPSIMD vector
> registers in the hardware.  To avoid any ambiguity about which
> alias to restore during sigreturn, the kernel always restores bits
> 127:0 of each SVE vector register from the fpsimd_context in the
> signal frame (which must be present): userspace needs to take this
> into account if it wants to modify the SVE vector register contents
> on return from a signal.
> 
> FPSR and FPCR, which are used by both FPSIMD and SVE, are not
> included in sve_context because they are always present in
> fpsimd_context anyway.
> 
> For signal delivery, a new helper
> fpsimd_signal_preserve_current_state() is added to update _both_
> the FPSIMD and SVE views in the task struct, to make it easier to
> populate this information into the signal frame.  Because of the
> redundancy between the two views of the state, only one is updated
> otherwise.
> 
> Signed-off-by: Dave Martin <Dave.Martin at arm.com>
> Cc: Alex Bennée <alex.bennee at linaro.org>
> Cc: Ard Biesheuvel <ard.biesheuvel at linaro.org>

Reviewed-by: Catalin Marinas <catalin.marinas at arm.com>