criu/mem: dump: skip MADV_GUARD pages content dump

1. get info about MADV_GUARD_INSTALL-protected pages with
help of pagemap by looking for PME_GUARD_REGION flag if /proc/<pid>/pagemap
is used or by looking for PAGE_IS_GUARD flag if ioctl(PAGEMAP_SCAN) is used
2. skip those pages

Signed-off-by: Alexander Mikhalitsyn <[email protected]>

Author: mihalicyn

criu/include/mem.h

@@ -35,6 +35,7 @@ extern int parasite_dump_pages_seized(struct pstree_item *item, struct vm_area_l
 #define PME_PRESENT	  (1ULL << 63)
 #define PME_SWAP	  (1ULL << 62)
 #define PME_FILE	  (1ULL << 61)
+#define PME_GUARD_REGION  (1ULL << 58)
 #define PME_SOFT_DIRTY	  (1ULL << 55)
 #define PME_PSHIFT_BITS	  (6)
 #define PME_STATUS_BITS	  (3)

criu/mem.c

@@ -143,12 +143,18 @@ int should_dump_page(pmc_t *pmc, VmaEntry *vmae, u64 vaddr, struct page_info *pa
 			return 0;
 		}
 
+		if (pmc->regs[pmc->regs_idx].categories & PAGE_IS_GUARD)
+			goto skip_guard_page;
+
 		page_info->softdirty = pmc->regs[pmc->regs_idx].categories & PAGE_IS_SOFT_DIRTY;
 		page_info->next = vaddr;
 		return 0;
 	} else {
 		u64 pme = pmc->map[PAGE_PFN(vaddr - pmc->start)];
 
+		if (pme & PME_GUARD_REGION)
+			goto skip_guard_page;
+
 		/*
 		 * Optimisation for private mapping pages, that haven't
 		 * yet being COW-ed
@@ -173,6 +179,10 @@ int should_dump_page(pmc_t *pmc, VmaEntry *vmae, u64 vaddr, struct page_info *pa
 	       "%#016" PRIx64 "-%#016" PRIx64 " vaddr=%#016" PRIx64 "\n",
 	       vmae->start, vmae->end, vaddr);
 	return -1;
+
+skip_guard_page:
+	page_info->next = vaddr + PAGE_SIZE;
+	return 0;
 }
 
 bool page_is_zero(u64 pme)