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RISC-V: exclude reserved memory regions

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The device tree may contain a "reserved-memory" node, whose purpose is
to communicate sections of physical memory that should not be used for
general allocations. Add the logic to parse and exclude these regions.

The particular motivation for this is protection of the SBI runtime
firmware. Currently, there is no mechanism through which the SBI
can communicate the details of its reserved memory region(s) to
a supervisor payload. There has been some discussion recently on how
this can be achieved [1], and it seems that the path going forward
will be to add an entry to the reserved-memory node.

This hasn't caused any issues for us yet, since we exclude all physical
memory below the kernel's load address from being allocated, and on all
currently supported platforms this covers the SBI firmware region. This
will change in another commit, so as a safety measure, ensure that the
lowest 2MB of memory is excluded if this region has not been reported.

[1] https://github.com/riscv/riscv-sbi-doc/pull/37

Reviewed by:	markj, nick (older version)
Differential Revision:	https://reviews.freebsd.org/D24155
This commit is contained in:
Mitchell Horne 2020-04-19 00:33:05 +00:00
parent 820a3f438d
commit f2566be5ce
1 changed files with 25 additions and 0 deletions
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25
sys/riscv/riscv/machdep.c
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@ -84,6 +84,7 @@ __FBSDID("$FreeBSD$");
#include <machine/machdep.h>
#include <machine/metadata.h>
#include <machine/pcb.h>
#include <machine/pte.h>
#include <machine/reg.h>
#include <machine/riscvreg.h>
#include <machine/sbi.h>
@ -827,6 +828,15 @@ initriscv(struct riscv_bootparams *rvbp)
#ifdef FDT
try_load_dtb(kmdp);
/*
* Exclude reserved memory specified by the device tree. Typically,
* this contains an entry for memory used by the runtime SBI firmware.
*/
if (fdt_get_reserved_mem(mem_regions, &mem_regions_sz) == 0) {
physmem_exclude_regions(mem_regions, mem_regions_sz,
EXFLAG_NODUMP | EXFLAG_NOALLOC);
}
/* Grab physical memory regions information from device tree. */
if (fdt_get_mem_regions(mem_regions, &mem_regions_sz, NULL) != 0) {
panic("Cannot get physical memory regions");
@ -843,6 +853,21 @@ initriscv(struct riscv_bootparams *rvbp)
kernlen = (lastaddr - KERNBASE);
pmap_bootstrap(rvbp->kern_l1pt, mem_regions[0].mr_start, kernlen);
#ifdef FDT
/*
* XXX: Exclude the lowest 2MB of physical memory, if it hasn't been
* already, as this area is assumed to contain the SBI firmware. This
* is a little fragile, but it is consistent with the platforms we
* support so far.
*
* TODO: remove this when the all regular booting methods properly
* report their reserved memory in the device tree.
*/
if (mem_regions[0].mr_start == physmap[0]) {
physmem_exclude_region(mem_regions[0].mr_start, L2_SIZE,
EXFLAG_NODUMP | EXFLAG_NOALLOC);
}
#endif
physmem_init_kernel_globals();
/* Establish static device mappings */