New functions kthread_fpu_enter/exit.
The MI definitions don't do anything but maintain a flag, but MD code can define kthread_fpu_enter/exit_md to actually enable/disable the FPU. (These are almost pcu_load/discard on systems that use pcu(9), except they apply to all PCUs.) Discussed on tech-kern: https://mail-index.netbsd.org/tech-kern/2020/06/20/msg026524.html The proposed kthread flag KTHREAD_FPU is not included because I couldn't find any particular need for it that would not be covered by just calling kthread_fpu_enter/exit in the kthread function.
This commit is contained in:
riastradh
parent
eef82c7583
commit
7c54d842f7
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@ -1,4 +1,4 @@
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.\" $NetBSD: kthread.9,v 1.28 2015/04/21 11:10:29 pooka Exp $
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.\" $NetBSD: kthread.9,v 1.29 2020/08/01 02:04:55 riastradh Exp $
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.\"
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.\" Copyright (c) 2000, 2007, 2008 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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@ -33,7 +33,9 @@
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.Sh NAME
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.Nm kthread_create ,
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.Nm kthread_exit ,
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.Nm kthread_join
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.Nm kthread_join ,
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.Nm kthread_fpu_enter ,
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.Nm kthread_fpu_exit
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.Nd kernel threads
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.Sh SYNOPSIS
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.In sys/kthread.h
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@ -44,6 +46,10 @@
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.Fn kthread_exit "int ecode"
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.Ft int
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.Fn kthread_join "lwp_t *l"
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.Ft int
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.Fn kthread_fpu_enter
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.Ft void
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.Fn kthread_fpu_exit "int s"
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.Sh DESCRIPTION
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Kernel threads are light-weight processes which execute entirely
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within the kernel.
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@ -51,6 +57,13 @@ within the kernel.
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Any process can request the creation of a new kernel thread.
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Kernel threads are not swapped out during memory congestion.
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The VM space and limits are shared with proc0 (usually swapper).
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.Pp
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If the machine has any per-CPU floating-point units or SIMD vector
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units that are normally available to user threads, they can be used by
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kthreads between
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.Fn kthread_fpu_enter
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and
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.fn kthread_fpu_exit .
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.Sh FUNCTIONS
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.Bl -tag -width compact
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.It Fn kthread_create "pri" "flags" "ci" "func" "arg" "newlp" "fmt" "..."
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@ -155,6 +168,31 @@ created using the
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.Dv KTHREAD_MUSTJOIN
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flag and would wait on
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.Fa kthread_exit .
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.It Fn kthread_fpu_enter
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Allow the current kthread to use any machine-dependent per-CPU
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floating-point units or SIMD vector units normally available to user
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threads.
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Returns a cookie that must be passed to
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.Fn kthread_fpu_exit
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when done.
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.Pp
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Matching pairs of
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.Fn kthread_fpu_enter
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and
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.Fn kthread_fpu_exit
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may be nested.
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.It Fn kthread_fpu_exit "s"
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Restore the current kthread's access to machine-dependent per-CPU
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floating-point units or SIMD vector units to what it was before the
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call to
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.Fn kthread_fpu_enter
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that returned
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.Fa s .
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.Pp
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On the last
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.Fn kthread_fpu_exit ,
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zero all the units' registers to avoid leaking secrets \(em such units
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are often used for cryptography.
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.El
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.Sh RETURN VALUES
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Upon successful completion,
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@ -1,4 +1,4 @@
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/* $NetBSD: kern_kthread.c,v 1.45 2020/01/08 17:38:42 ad Exp $ */
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/* $NetBSD: kern_kthread.c,v 1.46 2020/08/01 02:04:55 riastradh Exp $ */
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/*-
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* Copyright (c) 1998, 1999, 2007, 2009, 2019 The NetBSD Foundation, Inc.
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@ -31,9 +31,10 @@
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*/
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#include <sys/cdefs.h>
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__KERNEL_RCSID(0, "$NetBSD: kern_kthread.c,v 1.45 2020/01/08 17:38:42 ad Exp $");
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__KERNEL_RCSID(0, "$NetBSD: kern_kthread.c,v 1.46 2020/08/01 02:04:55 riastradh Exp $");
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#include <sys/param.h>
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#include <sys/cpu.h>
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#include <sys/systm.h>
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#include <sys/kernel.h>
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#include <sys/kthread.h>
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@ -216,3 +217,71 @@ kthread_join(lwp_t *l)
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return 0;
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}
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/*
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* kthread_fpu_enter()
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*
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* Allow the current lwp, which must be a kthread, to use the FPU.
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* Return a cookie that must be passed to kthread_fpu_exit when
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* done. Must be used only in thread context. Recursive -- you
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* can call kthread_fpu_enter several times in a row as long as
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* you pass the cookies in reverse order to kthread_fpu_exit.
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*/
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int
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kthread_fpu_enter(void)
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{
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struct lwp *l = curlwp;
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int s;
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KASSERTMSG(!cpu_intr_p(),
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"%s is not allowed in interrupt context", __func__);
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KASSERTMSG(!cpu_softintr_p(),
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"%s is not allowed in interrupt context", __func__);
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/*
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* Remember whether this thread already had FPU access, and
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* mark this thread as having FPU access.
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*/
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lwp_lock(l);
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KASSERTMSG(l->l_flag & LW_SYSTEM,
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"%s is allowed only in kthreads", __func__);
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s = l->l_flag & LW_SYSTEM_FPU;
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l->l_flag |= LW_SYSTEM_FPU;
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lwp_unlock(l);
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/* Take MD steps to enable the FPU if necessary. */
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if (s == 0)
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kthread_fpu_enter_md();
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return s;
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}
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/*
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* kthread_fpu_exit(s)
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*
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* Restore the current lwp's FPU access to what it was before the
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* matching call to kthread_fpu_enter() that returned s. Must be
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* used only in thread context.
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*/
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void
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kthread_fpu_exit(int s)
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{
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struct lwp *l = curlwp;
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KASSERT(s == (s & LW_SYSTEM_FPU));
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KASSERTMSG(!cpu_intr_p(),
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"%s is not allowed in interrupt context", __func__);
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KASSERTMSG(!cpu_softintr_p(),
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"%s is not allowed in interrupt context", __func__);
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lwp_lock(l);
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KASSERTMSG(l->l_flag & LW_SYSTEM,
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"%s is allowed only in kthreads", __func__);
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KASSERT(l->l_flag & LW_SYSTEM_FPU);
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l->l_flag ^= s ^ LW_SYSTEM_FPU;
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lwp_unlock(l);
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/* Take MD steps to zero and disable the FPU if necessary. */
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if (s == 0)
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kthread_fpu_exit_md();
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}
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@ -1,4 +1,4 @@
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/* $NetBSD: kern_stub.c,v 1.49 2020/05/23 23:42:43 ad Exp $ */
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/* $NetBSD: kern_stub.c,v 1.50 2020/08/01 02:04:55 riastradh Exp $ */
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/*-
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* Copyright (c) 2007, 2008 The NetBSD Foundation, Inc.
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@ -62,7 +62,7 @@
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*/
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#include <sys/cdefs.h>
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__KERNEL_RCSID(0, "$NetBSD: kern_stub.c,v 1.49 2020/05/23 23:42:43 ad Exp $");
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__KERNEL_RCSID(0, "$NetBSD: kern_stub.c,v 1.50 2020/08/01 02:04:55 riastradh Exp $");
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#ifdef _KERNEL_OPT
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#include "opt_ktrace.h"
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@ -328,3 +328,7 @@ default_bus_space_is_equal(bus_space_tag_t t1, bus_space_tag_t t2)
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return memcmp(&t1, &t2, sizeof(t1)) == 0;
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}
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/* Stubs for architectures with no kernel FPU access. */
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__weak_alias(kthread_fpu_enter_md, voidop);
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__weak_alias(kthread_fpu_exit_md, voidop);
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@ -1,4 +1,4 @@
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/* $NetBSD: kthread.h,v 1.13 2015/04/21 11:10:29 pooka Exp $ */
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/* $NetBSD: kthread.h,v 1.14 2020/08/01 02:04:55 riastradh Exp $ */
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/*-
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* Copyright (c) 1998, 2007, 2009 The NetBSD Foundation, Inc.
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@ -56,4 +56,11 @@ int kthread_create(pri_t, int, struct cpu_info *,
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void kthread_exit(int) __dead;
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int kthread_join(lwp_t *);
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int kthread_fpu_enter(void);
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void kthread_fpu_exit(int);
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/* Internal MD routines -- for use only by kthread_fpu_enter/exit. */
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void kthread_fpu_enter_md(void);
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void kthread_fpu_exit_md(void);
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#endif /* _SYS_KTHREAD_H_ */
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@ -1,4 +1,4 @@
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/* $NetBSD: lwp.h,v 1.210 2020/05/23 20:45:11 ad Exp $ */
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/* $NetBSD: lwp.h,v 1.211 2020/08/01 02:04:55 riastradh Exp $ */
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/*
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* Copyright (c) 2001, 2006, 2007, 2008, 2009, 2010, 2019, 2020
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@ -256,6 +256,7 @@ extern int maxlwp __read_mostly; /* max number of lwps */
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#define LW_STIMO 0x00000040 /* Sleep timed out */
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#define LW_SINTR 0x00000080 /* Sleep is interruptible. */
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#define LW_SYSTEM 0x00000200 /* Kernel thread */
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#define LW_SYSTEM_FPU 0x00000400 /* Kernel thread with vector/FP enabled */
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#define LW_DBGSUSPEND 0x00010000 /* Suspend by debugger */
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#define LW_WSUSPEND 0x00020000 /* Suspend before return to user */
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#define LW_BATCH 0x00040000 /* LWP tends to hog CPU */
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