svn commit: r360084 - head/sys/riscv/riscv

[Mitchell Horne]

Author: mhorne
Date: Sun Apr 19 00:33:05 2020
New Revision: 360084
URL: https://svnweb.freebsd.org/changeset/base/360084

Log:
  RISC-V: exclude reserved memory regions
  
  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

Modified:
  head/sys/riscv/riscv/machdep.c

Modified: head/sys/riscv/riscv/machdep.c
==============================================================================
--- head/sys/riscv/riscv/machdep.c	Sun Apr 19 00:18:16 2020	(r360083)
+++ head/sys/riscv/riscv/machdep.c	Sun Apr 19 00:33:05 2020	(r360084)
@@ -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 */