Date: Wed, 12 Feb 2020 18:00:41 -0800 From: Mark Millard <marklmi@yahoo.com> To: freebsd-arm <freebsd-arm@freebsd.org>, Kyle Evans <kevans@FreeBSD.org>, gonzo@freebsd.org Cc: Andrew Turner <andrew@freebsd.org>, Emmanuel Vadot <manu@freebsd.org> Subject: A investigative hack that makes (for example) head -r356529 boot and operate normally an RPi4B (finally!): protect all armstub8-gic.bin's loaded content from replacement by the kernel Message-ID: <7E7605DC-021D-448A-8459-8EC26BA9836D@yahoo.com> References: <7E7605DC-021D-448A-8459-8EC26BA9836D.ref@yahoo.com>
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[head -r356529 was just handy in my context.
I expect this works for head -r356776 and
later and probably before the problem was
exposed as well.]
The technique here is a quick hack to give
evidence for what correct, general code
needs to do that is not being done ( given
the head -r356776 changes exposing an
assumption no longer true and the use
of the FreeBSD specific armstub8-gic.bin
in my test context but armstub8.bin in
some other contexts).
I put in code to add a reserved memory region
spanning the 2 pages at the beginning of the
address space. This is enough to span all the
armstub8-gic.bin content (that is loaded to
address 0x0 in my test context).
Note the first listed memory region in:
Excluded memory regions:
0x00000000 - 0x00001fff, 0 MB ( 2 pages) NoAlloc NoDump
0x00000000 - 0x00000fff, 0 MB ( 1 pages) NoAlloc
. . .
My hack added that 2 page range as if it was in
memreserve in the live DTB. I already had the
failover code for fdt_get_reserved_mem to call
fdt_get_reserved_regions (to try for memreserve
when /reserved-memory is not found).
So here is what enabled the "boots and operates
normally" status for the RPi4B with a -r356776
or later version of head (yes, all 4 cores
operating):
# svnlite diff /usr/src/sys/dev/fdt/fdt_common.c
Index: /usr/src/sys/dev/fdt/fdt_common.c
===================================================================
--- /usr/src/sys/dev/fdt/fdt_common.c (revision 357529)
+++ /usr/src/sys/dev/fdt/fdt_common.c (working copy)
@@ -485,7 +485,18 @@
tuples = res_len / tuple_size;
reservep = (pcell_t *)&reserve;
+#ifdef __aarch64__
+ //HACK!!!
+ // Reserve the first few pages, for example to
+ // preserve armstub8-gic.bin or armstub.bin
+ // content.
+ mr[0].mr_start= 0;
+ mr[0].mr_size= 2*4096;
+ tuples++;
+ for (i = 1; i < tuples; i++) {
+#else
for (i = 0; i < tuples; i++) {
+#endif
rv = fdt_data_to_res(reservep, addr_cells, size_cells,
(u_long *)&mr[i].mr_start, (u_long *)&mr[i].mr_size);
@@ -512,6 +523,11 @@
root = OF_finddevice("/reserved-memory");
if (root == -1) {
+ // Fail over to checking for and handling memreserve,
+ // such as for a RPi4B.
+ if (0 == fdt_get_reserved_regions(reserved,mreserved))
+ return (0);
+
return (ENXIO);
}
I had done other investigative work earlier to
find for sure where armstub8-gic.bin was being
loaded in my example context: address 0x0.
I'm not trying to imply that assuming that load
address is appropriate. I simply do not know how
general address 0x0 is.
I'm only trying to imply that the page range
that ends up containing the armstub8*.bin
content should be excluded from what the kernel
will use for allocations.
I'm not trying to imply that DTB memreserve
content should be the involved. The memreserve
related code just happened to be where I
choose to do the "exclude more" hack.
I expect that causing the pages holding
armstub*.bin content to be excluded from FreeBSD
writing to any of those pages would also enable
RPi3's and the like to boot and operate as aarch64
FreeBSD examples for head -r356776 (and later,
other than other bugs). It did for the RPi4B
4 GiByte test context I used.
===
Mark Millard
marklmi at yahoo.com
( dsl-only.net went
away in early 2018-Mar)
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