[[PATCH] v4 1/4] riscv: vector: refactor vector context operations
Anup Patel
anup at brainfault.org
Tue Jul 7 09:05:18 PDT 2026
On Fri, May 29, 2026 at 12:41 AM Andy Chiu <tchiu at tenstorrent.com> wrote:
>
> Lift riscv_v_{enable,disable} out of __*vstate_{save,restore,discard} so
> that we can reuse some functions without repeatedly turning on/off
> vector.
>
> Also, refactor and document about the user context save in preempt_v to
> make code more readable.
>
> Signed-off-by: Andy Chiu <tchiu at tenstorrent.com>
For KVM RISC-V:
Acked-by: Anup Patel <anup at brainfault.org>
Regards,
Anup
> ---
> Changelog v4:
> - fix an unused variable warning (Olof)
> Changelog v3:
> - new patch since v3
> ---
> arch/riscv/include/asm/kvm_vcpu_vector.h | 8 +++++--
> arch/riscv/include/asm/vector.h | 15 ++++++------
> arch/riscv/kernel/kernel_mode_vector.c | 29 +++++++++++++++++++-----
> arch/riscv/kvm/vcpu_vector.c | 8 +++----
> 4 files changed, 41 insertions(+), 19 deletions(-)
>
> diff --git a/arch/riscv/include/asm/kvm_vcpu_vector.h b/arch/riscv/include/asm/kvm_vcpu_vector.h
> index 57a798a4cb0d..e679869e2ba3 100644
> --- a/arch/riscv/include/asm/kvm_vcpu_vector.h
> +++ b/arch/riscv/include/asm/kvm_vcpu_vector.h
> @@ -16,14 +16,18 @@
> #include <asm/vector.h>
> #include <asm/kvm_host.h>
>
> -static __always_inline void __kvm_riscv_vector_save(struct kvm_cpu_context *context)
> +static __always_inline void kvm_riscv_vector_save(struct kvm_cpu_context *context)
> {
> + riscv_v_enable();
> __riscv_v_vstate_save(&context->vector, context->vector.datap);
> + riscv_v_disable();
> }
>
> -static __always_inline void __kvm_riscv_vector_restore(struct kvm_cpu_context *context)
> +static __always_inline void kvm_riscv_vector_restore(struct kvm_cpu_context *context)
> {
> + riscv_v_enable();
> __riscv_v_vstate_restore(&context->vector, context->vector.datap);
> + riscv_v_disable();
> }
>
> void kvm_riscv_vcpu_vector_reset(struct kvm_vcpu *vcpu);
> diff --git a/arch/riscv/include/asm/vector.h b/arch/riscv/include/asm/vector.h
> index 00cb9c0982b1..45820cd900d6 100644
> --- a/arch/riscv/include/asm/vector.h
> +++ b/arch/riscv/include/asm/vector.h
> @@ -198,7 +198,6 @@ static inline void __riscv_v_vstate_save(struct __riscv_v_ext_state *save_to,
> {
> unsigned long vl;
>
> - riscv_v_enable();
> __vstate_csr_save(save_to);
> if (has_xtheadvector()) {
> asm volatile (
> @@ -227,7 +226,6 @@ static inline void __riscv_v_vstate_save(struct __riscv_v_ext_state *save_to,
> ".option pop\n\t"
> : "=&r" (vl) : "r" (datap) : "memory");
> }
> - riscv_v_disable();
> }
>
> static inline void __riscv_v_vstate_restore(struct __riscv_v_ext_state *restore_from,
> @@ -235,7 +233,6 @@ static inline void __riscv_v_vstate_restore(struct __riscv_v_ext_state *restore_
> {
> unsigned long vl;
>
> - riscv_v_enable();
> if (has_xtheadvector()) {
> asm volatile (
> "mv t0, %0\n\t"
> @@ -264,14 +261,12 @@ static inline void __riscv_v_vstate_restore(struct __riscv_v_ext_state *restore_
> : "=&r" (vl) : "r" (datap) : "memory");
> }
> __vstate_csr_restore(restore_from);
> - riscv_v_disable();
> }
>
> static inline void __riscv_v_vstate_discard(void)
> {
> unsigned long vl, vtype_inval = 1UL << (BITS_PER_LONG - 1);
>
> - riscv_v_enable();
> if (has_xtheadvector())
> asm volatile (THEAD_VSETVLI_T4X0E8M8D1 : : : "t4");
> else
> @@ -291,14 +286,14 @@ static inline void __riscv_v_vstate_discard(void)
> "vsetvl %0, x0, %1\n\t"
> ".option pop\n\t"
> : "=&r" (vl) : "r" (vtype_inval));
> -
> - riscv_v_disable();
> }
>
> static inline void riscv_v_vstate_discard(struct pt_regs *regs)
> {
> if (riscv_v_vstate_query(regs)) {
> + riscv_v_enable();
> __riscv_v_vstate_discard();
> + riscv_v_disable();
> __riscv_v_vstate_dirty(regs);
> }
> }
> @@ -307,7 +302,9 @@ static inline void riscv_v_vstate_save(struct __riscv_v_ext_state *vstate,
> struct pt_regs *regs)
> {
> if (__riscv_v_vstate_check(regs->status, DIRTY)) {
> + riscv_v_enable();
> __riscv_v_vstate_save(vstate, vstate->datap);
> + riscv_v_disable();
> __riscv_v_vstate_clean(regs);
> }
> }
> @@ -316,7 +313,9 @@ static inline void riscv_v_vstate_restore(struct __riscv_v_ext_state *vstate,
> struct pt_regs *regs)
> {
> if (riscv_v_vstate_query(regs)) {
> + riscv_v_enable();
> __riscv_v_vstate_restore(vstate, vstate->datap);
> + riscv_v_disable();
> __riscv_v_vstate_clean(regs);
> }
> }
> @@ -378,8 +377,10 @@ static inline void __switch_to_vector(struct task_struct *prev,
> prev->thread.riscv_v_flags |= RISCV_PREEMPT_V_IN_SCHEDULE;
> }
> if (riscv_preempt_v_dirty(prev)) {
> + riscv_v_enable();
> __riscv_v_vstate_save(&prev->thread.kernel_vstate,
> prev->thread.kernel_vstate.datap);
> + riscv_v_disable();
> riscv_preempt_v_clear_dirty(prev);
> }
> } else {
> diff --git a/arch/riscv/kernel/kernel_mode_vector.c b/arch/riscv/kernel/kernel_mode_vector.c
> index 99972a48e86b..21127b33fea8 100644
> --- a/arch/riscv/kernel/kernel_mode_vector.c
> +++ b/arch/riscv/kernel/kernel_mode_vector.c
> @@ -123,7 +123,7 @@ static int riscv_v_stop_kernel_context(void)
>
> static int riscv_v_start_kernel_context(bool *is_nested)
> {
> - struct __riscv_v_ext_state *kvstate, *uvstate;
> + struct __riscv_v_ext_state *kvstate;
>
> kvstate = ¤t->thread.kernel_vstate;
> if (!kvstate->datap)
> @@ -134,20 +134,35 @@ static int riscv_v_start_kernel_context(bool *is_nested)
> *is_nested = true;
> get_cpu_vector_context();
> if (riscv_preempt_v_dirty(current)) {
> + riscv_v_enable();
> __riscv_v_vstate_save(kvstate, kvstate->datap);
> + riscv_v_disable();
> riscv_preempt_v_clear_dirty(current);
> }
> riscv_preempt_v_set_restore(current);
> return 0;
> }
>
> - /* Transfer the ownership of V from user to kernel, then save */
> - riscv_v_start(RISCV_PREEMPT_V | RISCV_PREEMPT_V_DIRTY);
> + /*
> + * Skip saving user's context if it is not DIRTY. We would have to start KMV in "dirty" if
> + * this check is performed after KMV starts, to protect user's ctx. Then, we could waste
> + * time saving already "clean" context once KMV is started in "dirty".
> + */
> if (__riscv_v_vstate_check(task_pt_regs(current)->status, DIRTY)) {
> - uvstate = ¤t->thread.vstate;
> - __riscv_v_vstate_save(uvstate, uvstate->datap);
> + /* Transfer the ownership of V from user to kernel, then save */
> + riscv_v_start(RISCV_PREEMPT_V | RISCV_PREEMPT_V_DIRTY);
> + /*
> + * Calling the guarded version of vstate_save to make the code cleaner. Also, the
> + * vstate check within the call is necessary as context switch may happen between
> + * __riscv_v_vstate_check and riscv_v_start. In such case we are not supposed to
> + * save the context again.
> + */
> + riscv_v_vstate_save(¤t->thread.vstate, task_pt_regs(current));
> + riscv_preempt_v_clear_dirty(current);
> + return 0;
> }
> - riscv_preempt_v_clear_dirty(current);
> +
> + riscv_v_start(RISCV_PREEMPT_V);
> return 0;
> }
>
> @@ -180,7 +195,9 @@ asmlinkage void riscv_v_context_nesting_end(struct pt_regs *regs)
> depth = riscv_v_ctx_get_depth();
> if (depth == 0) {
> if (riscv_preempt_v_restore(current)) {
> + riscv_v_enable();
> __riscv_v_vstate_restore(vstate, vstate->datap);
> + riscv_v_disable();
> __riscv_v_vstate_clean(regs);
> riscv_preempt_v_reset_flags();
> }
> diff --git a/arch/riscv/kvm/vcpu_vector.c b/arch/riscv/kvm/vcpu_vector.c
> index 62d2fb77bb9b..da6c6db846c1 100644
> --- a/arch/riscv/kvm/vcpu_vector.c
> +++ b/arch/riscv/kvm/vcpu_vector.c
> @@ -46,7 +46,7 @@ void kvm_riscv_vcpu_guest_vector_save(struct kvm_cpu_context *cntx,
> {
> if ((cntx->sstatus & SR_VS) == SR_VS_DIRTY) {
> if (riscv_isa_extension_available(isa, v))
> - __kvm_riscv_vector_save(cntx);
> + kvm_riscv_vector_save(cntx);
> kvm_riscv_vcpu_vector_clean(cntx);
> }
> }
> @@ -56,7 +56,7 @@ void kvm_riscv_vcpu_guest_vector_restore(struct kvm_cpu_context *cntx,
> {
> if ((cntx->sstatus & SR_VS) != SR_VS_OFF) {
> if (riscv_isa_extension_available(isa, v))
> - __kvm_riscv_vector_restore(cntx);
> + kvm_riscv_vector_restore(cntx);
> kvm_riscv_vcpu_vector_clean(cntx);
> }
> }
> @@ -65,13 +65,13 @@ void kvm_riscv_vcpu_host_vector_save(struct kvm_cpu_context *cntx)
> {
> /* No need to check host sstatus as it can be modified outside */
> if (!kvm_riscv_isa_check_host(V))
> - __kvm_riscv_vector_save(cntx);
> + kvm_riscv_vector_save(cntx);
> }
>
> void kvm_riscv_vcpu_host_vector_restore(struct kvm_cpu_context *cntx)
> {
> if (!kvm_riscv_isa_check_host(V))
> - __kvm_riscv_vector_restore(cntx);
> + kvm_riscv_vector_restore(cntx);
> }
>
> int kvm_riscv_vcpu_alloc_vector_context(struct kvm_vcpu *vcpu)
> --
> 2.43.0
>
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