CVS commit: src/sys/arch

["Maxime Villard" <maxv%netbsd.org@localhost>]

Module Name:    src
Committed By:   maxv
Date:           Fri Jan  5 08:04:21 UTC 2018

Modified Files:
        src/sys/arch/amd64/amd64: gdt.c machdep.c
        src/sys/arch/amd64/include: types.h
        src/sys/arch/x86/include: cpu.h pmap.h
        src/sys/arch/x86/x86: cpu.c pmap.c

Log Message:
Add a __HAVE_PCPU_AREA option, enabled by default on native amd64 but not
Xen.

With this option, the CPU structures that must always be present in the
CPU's page tables are moved on L4 slot 384, which means address
0xffffc00000000000.

A new pcpu_area structure is defined. It contains shared structures (IDT,
LDT), and then an array of pcpu_entry structures, indexed by cpu_index(ci).
Theoretically the LDT should be in the array, but this will be done later.

During the boot procedure, cpu0 calls pmap_init_pcpu, which creates a
page tree that is able to map the pcpu_area structure entirely. cpu0 then
immediately maps the shared structures. Later, every CPU goes through
cpu_pcpuarea_init, which allocates physical pages and kenters the relevant
pcpu_entry to them. Finally, each pointer is replaced to point to pcpuarea.

The point of this change is to make sure that the structures that must
always be present in the page tables have their own L4 slot. Until now
their L4 slot was that of pmap_kernel, and making a distinction between
what must be mapped and what does not need to be was complicated.

Even in the non-speculative-bug case this change makes some sense: there
are several x86 instructions that leak the addresses of the CPU structures,
and putting these structures inside pmap_kernel actually offered a way to
compute the address of the kernel heap - which would have made ASLR on it
plainly useless, had we implemented that.

Note that, for now, pcpuarea does not contain rsp0.

Unfortunately this change adds many #ifdefs, and makes the code harder to
understand. There is also some duplication, but that will be solved later.


To generate a diff of this commit:
cvs rdiff -u -r1.44 -r1.45 src/sys/arch/amd64/amd64/gdt.c
cvs rdiff -u -r1.283 -r1.284 src/sys/arch/amd64/amd64/machdep.c
cvs rdiff -u -r1.52 -r1.53 src/sys/arch/amd64/include/types.h
cvs rdiff -u -r1.86 -r1.87 src/sys/arch/x86/include/cpu.h
cvs rdiff -u -r1.72 -r1.73 src/sys/arch/x86/include/pmap.h
cvs rdiff -u -r1.141 -r1.142 src/sys/arch/x86/x86/cpu.c
cvs rdiff -u -r1.275 -r1.276 src/sys/arch/x86/x86/pmap.c

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.