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Large user copy_to/from (more than 16 bytes) uses vmx instructions to speed things up. Once the copy is done, it makes sense to try schedule as soon as possible for preemptible kernels. So do this for preempt=full/lazy and rt kernel. Not checking for lazy bit here, since it could lead to unnecessary context switches. Suggested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com> Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com> Link: https://patch.msgid.link/20241116192306.88217-3-sshegde@linux.ibm.com
76 lines
1.7 KiB
C
76 lines
1.7 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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*
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* Copyright (C) IBM Corporation, 2011
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*
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* Authors: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
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* Anton Blanchard <anton@au.ibm.com>
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*/
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#include <linux/uaccess.h>
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#include <linux/hardirq.h>
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#include <asm/switch_to.h>
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int enter_vmx_usercopy(void)
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{
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if (in_interrupt())
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return 0;
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preempt_disable();
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/*
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* We need to disable page faults as they can call schedule and
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* thus make us lose the VMX context. So on page faults, we just
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* fail which will cause a fallback to the normal non-vmx copy.
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*/
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pagefault_disable();
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enable_kernel_altivec();
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return 1;
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}
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/*
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* This function must return 0 because we tail call optimise when calling
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* from __copy_tofrom_user_power7 which returns 0 on success.
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*/
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int exit_vmx_usercopy(void)
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{
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disable_kernel_altivec();
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pagefault_enable();
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preempt_enable_no_resched();
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/*
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* Must never explicitly call schedule (including preempt_enable())
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* while in a kuap-unlocked user copy, because the AMR register will
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* not be saved and restored across context switch. However preempt
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* kernels need to be preempted as soon as possible if need_resched is
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* set and we are preemptible. The hack here is to schedule a
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* decrementer to fire here and reschedule for us if necessary.
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*/
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if (IS_ENABLED(CONFIG_PREEMPTION) && need_resched())
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set_dec(1);
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return 0;
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}
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int enter_vmx_ops(void)
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{
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if (in_interrupt())
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return 0;
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preempt_disable();
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enable_kernel_altivec();
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return 1;
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}
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/*
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* All calls to this function will be optimised into tail calls. We are
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* passed a pointer to the destination which we return as required by a
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* memcpy implementation.
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*/
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void *exit_vmx_ops(void *dest)
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{
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disable_kernel_altivec();
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preempt_enable();
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return dest;
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}
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