1.) When I tested live system with "crash vmlinux /proc/kcore" in kernel v5.7,
I met the following crash issue:
........................................
crash: seek error: kernel virtual address: ffff75e9fffff000 type: "pud page"
........................................
2.) The root cause is the PTOV does not work correctly for some kernel,
and then arm64_vtop_4level_4k() does not work correctly too.
Why PTOV does not work?
Because the physvirt_offset does not get the correct value.
3.) This patch uses symbol_value_from_proc_kallsyms() to get the
virtual address of "physvirt_offset", and then uses
READMEM(,..,KCORE_USE_VADDR) to get the correct value of
"physvirt_offset".
And also updates the ms->phys_offset which is initialized with
a wrong value in kernel version [5.4, 5.10).
Also add more comments for arm64_calc_physvirt_offset().
Signed-off-by: Huang Shijie <shijie@xxxxxxxxxxxxxxxxxxxxxx>
---
v1 --> v2:
v1 tried to get the correct value for phys_offset,
and then get the physvirt_offset correctly.
v2 tried to get the physvirt_offset correctly,
and them update phys_offset correctly.
Tested this patch with kernel 5.7.
---
arm64.c | 28 ++++++++++++++++++++++++++++
1 file changed, 28 insertions(+)
diff --git a/arm64.c b/arm64.c
index b843032..60ae644 100644
--- a/arm64.c
+++ b/arm64.c
@@ -1399,15 +1399,43 @@ arm64_calc_kimage_voffset(void)
ms->kimage_voffset += (kt->relocate * -1);
}
+/*
+ * The physvirt_offset only exits in kernel [5.4, 5.10)
+ *
+ * 1) In kernel v5.4, the patch:
+ * "5383cc6efed137 arm64: mm: Introduce vabits_actual"
+ *
+ * introduced the physvirt_offset.
+ *
+ * 2) In kernel v5.10, the patch:
+ * "7bc1a0f9e17658 arm64: mm: use single quantity
+ * to represent the PA to VA translation"
+ * removed the physvirt_offset.
+ */
static void
arm64_calc_physvirt_offset(void)
{
struct machine_specific *ms = machdep->machspec;
ulong physvirt_offset;
struct syment *sp;
+ ulong value;
if ((sp = kernel_symbol_search("physvirt_offset")) &&
machdep->machspec->kimage_voffset) {
+ if (pc->flags & PROC_KCORE) {
+ value = symbol_value_from_proc_kallsyms("physvirt_offset");
+ if ((value != BADVAL) &&
+ (READMEM(pc->mfd, &physvirt_offset, sizeof(ulong),
+ value, KCORE_USE_VADDR) > 0)) {
+ machdep->flags |= HAS_PHYSVIRT_OFFSET;
+ ms->physvirt_offset = physvirt_offset;
+
+ /* Update the ms->phys_offset which is wrong */
+ ms->phys_offset = ms->physvirt_offset + ms->page_offset;
+ return;
+ }
+ }
+
if (READMEM(pc->mfd, &physvirt_offset, sizeof(physvirt_offset),
sp->value, sp->value -
machdep->machspec->kimage_voffset) > 0) {
--
2.30.2
--
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