crash_core: fix and simplify the logic of crash_exclude_mem_range()

The purpose of crash_exclude_mem_range() is to remove all memory ranges
that overlap with [mstart-mend].  However, the current logic only removes
the first overlapping memory range.

Commit a2e9a95d2190 ("kexec: Improve & fix crash_exclude_mem_range() to
handle overlapping ranges") attempted to address this issue, but it did
not fix all error cases.

Let's fix and simplify the logic of crash_exclude_mem_range().

Link: https://lkml.kernel.org/r/20240102144905.110047-4-ytcoode@gmail.com
Signed-off-by: Yuntao Wang <ytcoode@gmail.com>
Acked-by: Baoquan He <bhe@redhat.com>
Cc: Borislav Petkov (AMD) <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Hari Bathini <hbathini@linux.ibm.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Sourabh Jain <sourabhjain@linux.ibm.com>
Cc: Takashi Iwai <tiwai@suse.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 6f074e112c1e5f68f81b5b4f84939b628bd15386..62e0227d390eced9948e85fa2d18dda7f248973f 100644 (file)
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -566,9 +566,8 @@ int crash_prepare_elf64_headers(struct crash_mem *mem, int need_kernel_map,
 int crash_exclude_mem_range(struct crash_mem *mem,
                            unsigned long long mstart, unsigned long long mend)
 {
-       int i, j;
+       int i;
        unsigned long long start, end, p_start, p_end;
-       struct range temp_range = {0, 0};
 
        for (i = 0; i < mem->nr_ranges; i++) {
                start = mem->ranges[i].start;
@@ -576,72 +575,51 @@ int crash_exclude_mem_range(struct crash_mem *mem,
                p_start = mstart;
                p_end = mend;
 
-               if (mstart > end || mend < start)
+               if (p_start > end)
                        continue;
 
+               /*
+                * Because the memory ranges in mem->ranges are stored in
+                * ascending order, when we detect `p_end < start`, we can
+                * immediately exit the for loop, as the subsequent memory
+                * ranges will definitely be outside the range we are looking
+                * for.
+                */
+               if (p_end < start)
+                       break;
+
                /* Truncate any area outside of range */
-               if (mstart < start)
+               if (p_start < start)
                        p_start = start;
-               if (mend > end)
+               if (p_end > end)
                        p_end = end;
 
                /* Found completely overlapping range */
                if (p_start == start && p_end == end) {
-                       mem->ranges[i].start = 0;
-                       mem->ranges[i].end = 0;
-                       if (i < mem->nr_ranges - 1) {
-                               /* Shift rest of the ranges to left */
-                               for (j = i; j < mem->nr_ranges - 1; j++) {
-                                       mem->ranges[j].start =
-                                               mem->ranges[j+1].start;
-                                       mem->ranges[j].end =
-                                                       mem->ranges[j+1].end;
-                               }
-
-                               /*
-                                * Continue to check if there are another overlapping ranges
-                                * from the current position because of shifting the above
-                                * mem ranges.
-                                */
-                               i--;
-                               mem->nr_ranges--;
-                               continue;
-                       }
+                       memmove(&mem->ranges[i], &mem->ranges[i + 1],
+                               (mem->nr_ranges - (i + 1)) * sizeof(mem->ranges[i]));
+                       i--;
                        mem->nr_ranges--;
-                       return 0;
-               }
-
-               if (p_start > start && p_end < end) {
+               } else if (p_start > start && p_end < end) {
                        /* Split original range */
+                       if (mem->nr_ranges >= mem->max_nr_ranges)
+                               return -ENOMEM;
+
+                       memmove(&mem->ranges[i + 2], &mem->ranges[i + 1],
+                               (mem->nr_ranges - (i + 1)) * sizeof(mem->ranges[i]));
+
                        mem->ranges[i].end = p_start - 1;
-                       temp_range.start = p_end + 1;
-                       temp_range.end = end;
+                       mem->ranges[i + 1].start = p_end + 1;
+                       mem->ranges[i + 1].end = end;
+
+                       i++;
+                       mem->nr_ranges++;
                } else if (p_start != start)
                        mem->ranges[i].end = p_start - 1;
                else
                        mem->ranges[i].start = p_end + 1;
-               break;
-       }
-
-       /* If a split happened, add the split to array */
-       if (!temp_range.end)
-               return 0;
-
-       /* Split happened */
-       if (i == mem->max_nr_ranges - 1)
-               return -ENOMEM;
-
-       /* Location where new range should go */
-       j = i + 1;
-       if (j < mem->nr_ranges) {
-               /* Move over all ranges one slot towards the end */
-               for (i = mem->nr_ranges - 1; i >= j; i--)
-                       mem->ranges[i + 1] = mem->ranges[i];
        }
 
-       mem->ranges[j].start = temp_range.start;
-       mem->ranges[j].end = temp_range.end;
-       mem->nr_ranges++;
        return 0;
 }