d86c1f0dc1
The change makes the user and kernel address spaces on i386 independent, giving each almost the full 4G of usable virtual addresses except for one PDE at top used for trampoline and per-CPU trampoline stacks, and system structures that must be always mapped, namely IDT, GDT, common TSS and LDT, and process-private TSS and LDT if allocated. By using 1:1 mapping for the kernel text and data, it appeared possible to eliminate assembler part of the locore.S which bootstraps initial page table and KPTmap. The code is rewritten in C and moved into the pmap_cold(). The comment in vmparam.h explains the KVA layout. There is no PCID mechanism available in protected mode, so each kernel/user switch forth and back completely flushes the TLB, except for the trampoline PTD region. The TLB invalidations for userspace becomes trivial, because IPI handlers switch page tables. On the other hand, context switches no longer need to reload %cr3. copyout(9) was rewritten to use vm_fault_quick_hold(). An issue for new copyout(9) is compatibility with wiring user buffers around sysctl handlers. This explains two kind of locks for copyout ptes and accounting of the vslock() calls. The vm_fault_quick_hold() AKA slow path, is only tried after the 'fast path' failed, which temporary changes mapping to the userspace and copies the data to/from small per-cpu buffer in the trampoline. If a page fault occurs during the copy, it is short-circuit by exception.s to not even reach C code. The change was motivated by the need to implement the Meltdown mitigation, but instead of KPTI the full split is done. The i386 architecture already shows the sizing problems, in particular, it is impossible to link clang and lld with debugging. I expect that the issues due to the virtual address space limits would only exaggerate and the split gives more liveness to the platform. Tested by: pho Discussed with: bde Sponsored by: The FreeBSD Foundation MFC after: 1 month Differential revision: https://reviews.freebsd.org/D14633
100 lines
3.6 KiB
C
100 lines
3.6 KiB
C
/*-
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* SPDX-License-Identifier: BSD-3-Clause
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*
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* Copyright (c) 1989, 1990 William F. Jolitz
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* Copyright (c) 1990 The Regents of the University of California.
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* All rights reserved.
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*
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* This code is derived from software contributed to Berkeley by
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* William Jolitz.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* from: @(#)segments.h 7.1 (Berkeley) 5/9/91
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* $FreeBSD$
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*/
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#ifndef _MACHINE_SEGMENTS_H_
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#define _MACHINE_SEGMENTS_H_
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/*
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* 386 Segmentation Data Structures and definitions
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* William F. Jolitz (william@ernie.berkeley.edu) 6/20/1989
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*/
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#include <x86/segments.h>
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/*
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* Software definitions are in this convenient format,
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* which are translated into inconvenient segment descriptors
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* when needed to be used by the 386 hardware
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*/
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struct soft_segment_descriptor {
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unsigned ssd_base ; /* segment base address */
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unsigned ssd_limit ; /* segment extent */
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unsigned ssd_type:5 ; /* segment type */
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unsigned ssd_dpl:2 ; /* segment descriptor priority level */
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unsigned ssd_p:1 ; /* segment descriptor present */
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unsigned ssd_xx:4 ; /* unused */
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unsigned ssd_xx1:2 ; /* unused */
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unsigned ssd_def32:1 ; /* default 32 vs 16 bit size */
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unsigned ssd_gran:1 ; /* limit granularity (byte/page units)*/
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};
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/*
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* region descriptors, used to load gdt/idt tables before segments yet exist.
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*/
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struct region_descriptor {
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unsigned rd_limit:16; /* segment extent */
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unsigned rd_base:32 __packed; /* base address */
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};
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/*
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* Segment Protection Exception code bits
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*/
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#define SEGEX_EXT 0x01 /* recursive or externally induced */
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#define SEGEX_IDT 0x02 /* interrupt descriptor table */
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#define SEGEX_TI 0x04 /* local descriptor table */
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/* other bits are affected descriptor index */
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#define SEGEX_IDX(s) (((s)>>3)&0x1fff)
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#ifdef _KERNEL
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extern int _default_ldt;
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extern union descriptor *gdt;
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extern union descriptor *ldt;
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extern struct soft_segment_descriptor gdt_segs[];
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extern struct gate_descriptor *idt;
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void lgdt(struct region_descriptor *rdp);
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void sdtossd(struct segment_descriptor *sdp,
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struct soft_segment_descriptor *ssdp);
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void ssdtosd(struct soft_segment_descriptor *ssdp,
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struct segment_descriptor *sdp);
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#endif /* _KERNEL */
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#endif /* !_MACHINE_SEGMENTS_H_ */
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