riscv: vector: Fix a typo of preempt_v

The term "preempt_v" represents the RISCV_PREEMPT_V field of riscv_v_flags
and is used in lots of comments.

Here corrects the miss-spelling "prempt_v". And s/acheived/achieved/.

Reviewed-by: Andy Chiu <andybnac@gmail.com>
Signed-off-by: Song Shuai <songshuaishuai@tinylab.org>
Link: https://lore.kernel.org/r/20240221100252.3990445-1-songshuaishuai@tinylab.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

riscv: vector: allow kernel-mode Vector with preemption

Add kernel_vstate to keep track of kernel-mode Vector registers when
trap introduced context switch happens. Also, provide riscv_v_flags to
let context save/restore routine track context status. Context tracking
happens whenever the core starts its in-kernel Vector executions. An
active (dirty) kernel task's V contexts will be saved to memory whenever
a trap-introduced context switch happens. Or, when a softirq, which
happens to nest on top of it, uses Vector. Context retoring happens when
the execution transfer back to the original Kernel context where it
first enable preempt_v.

Also, provide a config CONFIG_RISCV_ISA_V_PREEMPTIVE to give users an
option to disable preemptible kernel-mode Vector at build time. Users
with constraint memory may want to disable this config as preemptible
kernel-mode Vector needs extra space for tracking of per thread's
kernel-mode V context. Or, users might as well want to disable it if all
kernel-mode Vector code is time sensitive and cannot tolerate context
switch overhead.

Signed-off-by: Andy Chiu <andy.chiu@sifive.com>
Tested-by: Björn Töpel <bjorn@rivosinc.com>
Tested-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Link: https://lore.kernel.org/r/20240115055929.4736-11-andy.chiu@sifive.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

riscv: vector: make Vector always available for softirq context

The goal of this patch is to provide full support of Vector in kernel
softirq context. So that some of the crypto alogrithms won't need scalar
fallbacks.

By disabling bottom halves in active kernel-mode Vector, softirq will
not be able to nest on top of any kernel-mode Vector. So, softirq
context is able to use Vector whenever it runs.

After this patch, Vector context cannot start with irqs disabled.
Otherwise local_bh_enable() may run in a wrong context.

Disabling bh is not enough for RT-kernel to prevent preeemption. So
we must disable preemption, which also implies disabling bh on RT.

Related-to: commit 696207d4258b ("arm64/sve: Make kernel FPU protection RT friendly")
Related-to: commit 66c3ec5a7120 ("arm64: neon: Forbid when irqs are disabled")
Signed-off-by: Andy Chiu <andy.chiu@sifive.com>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Tested-by: Björn Töpel <bjorn@rivosinc.com>
Tested-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Link: https://lore.kernel.org/r/20240115055929.4736-3-andy.chiu@sifive.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

riscv: Add support for kernel mode vector

Add kernel_vector_begin() and kernel_vector_end() function declarations
and corresponding definitions in kernel_mode_vector.c

These are needed to wrap uses of vector in kernel mode.

Co-developed-by: Vincent Chen <vincent.chen@sifive.com>
Signed-off-by: Vincent Chen <vincent.chen@sifive.com>
Signed-off-by: Greentime Hu <greentime.hu@sifive.com>
Signed-off-by: Andy Chiu <andy.chiu@sifive.com>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Tested-by: Björn Töpel <bjorn@rivosinc.com>
Tested-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Link: https://lore.kernel.org/r/20240115055929.4736-2-andy.chiu@sifive.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>