[Xen-devel] [PATCH v2] makedumpfile: exclude pages that are logically offline

[David Hildenbrand <david@xxxxxxxxxx>]

Linux marks pages that are logically offline via a page flag (map count).
Such pages e.g. include pages infated as part of a balloon driver or
pages that were not actually onlined when onlining the whole section.

While the hypervisor usually allows to read such inflated memory, we
basically read and dump data that is completely irrelevant. Also, this
might result in quite some overhead in the hypervisor. In addition,
we saw some problems under Hyper-V, whereby we can crash the kernel by
dumping, when reading memory of a partially onlined memory segment
(for memory added by the Hyper-V balloon driver).

Therefore, don't read and dump pages that are marked as being logically
offline.

Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---

v1 -> v2:
- Fix PAGE_BUDDY_MAPCOUNT_VALUE vs. PAGE_OFFLINE_MAPCOUNT_VALUE

 makedumpfile.c | 34 ++++++++++++++++++++++++++++++----
 makedumpfile.h |  1 +
 2 files changed, 31 insertions(+), 4 deletions(-)

diff --git a/makedumpfile.c b/makedumpfile.c
index 8923538..a5f2ea9 100644
--- a/makedumpfile.c
+++ b/makedumpfile.c
@@ -88,6 +88,7 @@ mdf_pfn_t pfn_cache_private;
 mdf_pfn_t pfn_user;
 mdf_pfn_t pfn_free;
 mdf_pfn_t pfn_hwpoison;
+mdf_pfn_t pfn_offline;
 
 mdf_pfn_t num_dumped;
 
@@ -249,6 +250,21 @@ isHugetlb(unsigned long dtor)
                     && (SYMBOL(free_huge_page) == dtor));
 }
 
+static int
+isOffline(unsigned long flags, unsigned int _mapcount)
+{
+       if (NUMBER(PAGE_OFFLINE_MAPCOUNT_VALUE) == NOT_FOUND_NUMBER)
+               return FALSE;
+
+       if (flags & (1UL << NUMBER(PG_slab)))
+               return FALSE;
+
+       if (_mapcount == (int)NUMBER(PAGE_OFFLINE_MAPCOUNT_VALUE))
+               return TRUE;
+
+       return FALSE;
+}
+
 static int
 is_cache_page(unsigned long flags)
 {
@@ -2287,6 +2303,8 @@ write_vmcoreinfo_data(void)
        WRITE_NUMBER("PG_hwpoison", PG_hwpoison);
 
        WRITE_NUMBER("PAGE_BUDDY_MAPCOUNT_VALUE", PAGE_BUDDY_MAPCOUNT_VALUE);
+       WRITE_NUMBER("PAGE_OFFLINE_MAPCOUNT_VALUE",
+                    PAGE_OFFLINE_MAPCOUNT_VALUE);
        WRITE_NUMBER("phys_base", phys_base);
 
        WRITE_NUMBER("HUGETLB_PAGE_DTOR", HUGETLB_PAGE_DTOR);
@@ -2687,6 +2705,7 @@ read_vmcoreinfo(void)
        READ_SRCFILE("pud_t", pud_t);
 
        READ_NUMBER("PAGE_BUDDY_MAPCOUNT_VALUE", PAGE_BUDDY_MAPCOUNT_VALUE);
+       READ_NUMBER("PAGE_OFFLINE_MAPCOUNT_VALUE", PAGE_OFFLINE_MAPCOUNT_VALUE);
        READ_NUMBER("phys_base", phys_base);
 #ifdef __aarch64__
        READ_NUMBER("VA_BITS", VA_BITS);
@@ -6041,6 +6060,12 @@ __exclude_unnecessary_pages(unsigned long mem_map,
                else if (isHWPOISON(flags)) {
                        pfn_counter = &pfn_hwpoison;
                }
+               /*
+                * Exclude pages that are logically offline.
+                */
+               else if (isOffline(flags, _mapcount)) {
+                       pfn_counter = &pfn_offline;
+               }
                /*
                 * Unexcludable page
                 */
@@ -7522,7 +7547,7 @@ write_elf_pages_cyclic(struct cache_data *cd_header, 
struct cache_data *cd_page)
         */
        if (info->flag_cyclic) {
                pfn_zero = pfn_cache = pfn_cache_private = 0;
-               pfn_user = pfn_free = pfn_hwpoison = 0;
+               pfn_user = pfn_free = pfn_hwpoison = pfn_offline = 0;
                pfn_memhole = info->max_mapnr;
        }
 
@@ -8804,7 +8829,7 @@ write_kdump_pages_and_bitmap_cyclic(struct cache_data 
*cd_header, struct cache_d
                 * Reset counter for debug message.
                 */
                pfn_zero = pfn_cache = pfn_cache_private = 0;
-               pfn_user = pfn_free = pfn_hwpoison = 0;
+               pfn_user = pfn_free = pfn_hwpoison = pfn_offline = 0;
                pfn_memhole = info->max_mapnr;
 
                /*
@@ -9749,7 +9774,7 @@ print_report(void)
        pfn_original = info->max_mapnr - pfn_memhole;
 
        pfn_excluded = pfn_zero + pfn_cache + pfn_cache_private
-           + pfn_user + pfn_free + pfn_hwpoison;
+           + pfn_user + pfn_free + pfn_hwpoison + pfn_offline;
        shrinking = (pfn_original - pfn_excluded) * 100;
        shrinking = shrinking / pfn_original;
 
@@ -9763,6 +9788,7 @@ print_report(void)
        REPORT_MSG("    User process data pages : 0x%016llx\n", pfn_user);
        REPORT_MSG("    Free pages              : 0x%016llx\n", pfn_free);
        REPORT_MSG("    Hwpoison pages          : 0x%016llx\n", pfn_hwpoison);
+       REPORT_MSG("    Offline pages           : 0x%016llx\n", pfn_offline);
        REPORT_MSG("  Remaining pages  : 0x%016llx\n",
            pfn_original - pfn_excluded);
        REPORT_MSG("  (The number of pages is reduced to %lld%%.)\n",
@@ -9790,7 +9816,7 @@ print_mem_usage(void)
        pfn_original = info->max_mapnr - pfn_memhole;
 
        pfn_excluded = pfn_zero + pfn_cache + pfn_cache_private
-           + pfn_user + pfn_free + pfn_hwpoison;
+           + pfn_user + pfn_free + pfn_hwpoison + pfn_offline;
        shrinking = (pfn_original - pfn_excluded) * 100;
        shrinking = shrinking / pfn_original;
        total_size = info->page_size * pfn_original;
diff --git a/makedumpfile.h b/makedumpfile.h
index f02f86d..e3a2b29 100644
--- a/makedumpfile.h
+++ b/makedumpfile.h
@@ -1927,6 +1927,7 @@ struct number_table {
        long    PG_hwpoison;
 
        long    PAGE_BUDDY_MAPCOUNT_VALUE;
+       long    PAGE_OFFLINE_MAPCOUNT_VALUE;
        long    SECTION_SIZE_BITS;
        long    MAX_PHYSMEM_BITS;
        long    HUGETLB_PAGE_DTOR;
-- 
2.17.2


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