powerpc/xmon: Support dumping software pagetables

It would be nice to be able to dump page tables in a particular
context.

eg: dumping vmalloc space:

0:mon> dv 0xd00037fffff00000
pgd @ 0xc0000000017c0000
pgdp @ 0xc0000000017c00d8 = 0x00000000f10b1000
pudp @ 0xc0000000f10b13f8 = 0x00000000f10d0000
pmdp @ 0xc0000000f10d1ff8 = 0x00000000f1102000
ptep @ 0xc0000000f1102780 = 0xc0000000f1ba018e
Maps physical address = 0x00000000f1ba0000
Flags = Accessed Dirty Read Write

This patch does not replicate the complex code of dump_pagetable and
has no support for bolted linear mapping, thats why I've it's called
dump virtual page table support. The format of the PTE can be expanded
even further to add more useful information about the flags in the PTE
if required.

Signed-off-by: Balbir Singh <[e-mail]>
[mpe: Bike shed the output format, show the pgdir, fix build failures]
Signed-off-by: Michael Ellerman <[e-mail]>

arch/powerpc/xmon/xmon.c

···
 #include <linux/bug.h>
 #include <linux/nmi.h>
 #include <linux/ctype.h>
+#include <linux/highmem.h>
 
 #include <asm/debugfs.h>
 #include <asm/ptrace.h>
···
 static void memex(void);
 static int bsesc(void);
 static void dump(void);
+static void show_pte(unsigned long);
 static void prdump(unsigned long, long);
 static int ppc_inst_dump(unsigned long, long, int);
 static void dump_log_buf(void);
···
 #endif
   "\
   dr	dump stream of raw bytes\n\
+  dv	dump virtual address translation \n\
   dt	dump the tracing buffers (uses printk)\n\
   dtc	dump the tracing buffers for current CPU (uses printk)\n\
 "
···
 		dump_log_buf();
 	} else if (c == 'o') {
 		dump_opal_msglog();
+	} else if (c == 'v') {
+		/* dump virtual to physical translation */
+		show_pte(adrs);
 	} else if (c == 'r') {
 		scanhex(&ndump);
 		if (ndump == 0)
···
 		state, task_thread_info(tsk)->cpu,
 		tsk->comm);
 }
+
+#ifdef CONFIG_PPC_BOOK3S_64
+void format_pte(void *ptep, unsigned long pte)
+{
+	printf("ptep @ 0x%016lx = 0x%016lx\n", (unsigned long)ptep, pte);
+	printf("Maps physical address = 0x%016lx\n", pte & PTE_RPN_MASK);
+
+	printf("Flags = %s%s%s%s%s\n",
+	       (pte & _PAGE_ACCESSED) ? "Accessed " : "",
+	       (pte & _PAGE_DIRTY)    ? "Dirty " : "",
+	       (pte & _PAGE_READ)     ? "Read " : "",
+	       (pte & _PAGE_WRITE)    ? "Write " : "",
+	       (pte & _PAGE_EXEC)     ? "Exec " : "");
+}
+
+static void show_pte(unsigned long addr)
+{
+	unsigned long tskv = 0;
+	struct task_struct *tsk = NULL;
+	struct mm_struct *mm;
+	pgd_t *pgdp, *pgdir;
+	pud_t *pudp;
+	pmd_t *pmdp;
+	pte_t *ptep;
+
+	if (!scanhex(&tskv))
+		mm = &init_mm;
+	else
+		tsk = (struct task_struct *)tskv;
+
+	if (tsk == NULL)
+		mm = &init_mm;
+	else
+		mm = tsk->active_mm;
+
+	if (setjmp(bus_error_jmp) != 0) {
+		catch_memory_errors = 0;
+		printf("*** Error dumping pte for task %p\n", tsk);
+		return;
+	}
+
+	catch_memory_errors = 1;
+	sync();
+
+	if (mm == &init_mm) {
+		pgdp = pgd_offset_k(addr);
+		pgdir = pgd_offset_k(0);
+	} else {
+		pgdp = pgd_offset(mm, addr);
+		pgdir = pgd_offset(mm, 0);
+	}
+
+	if (pgd_none(*pgdp)) {
+		printf("no linux page table for address\n");
+		return;
+	}
+
+	printf("pgd  @ 0x%016lx\n", pgdir);
+
+	if (pgd_huge(*pgdp)) {
+		format_pte(pgdp, pgd_val(*pgdp));
+		return;
+	}
+	printf("pgdp @ 0x%016lx = 0x%016lx\n", pgdp, pgd_val(*pgdp));
+
+	pudp = pud_offset(pgdp, addr);
+
+	if (pud_none(*pudp)) {
+		printf("No valid PUD\n");
+		return;
+	}
+
+	if (pud_huge(*pudp)) {
+		format_pte(pudp, pud_val(*pudp));
+		return;
+	}
+
+	printf("pudp @ 0x%016lx = 0x%016lx\n", pudp, pud_val(*pudp));
+
+	pmdp = pmd_offset(pudp, addr);
+
+	if (pmd_none(*pmdp)) {
+		printf("No valid PMD\n");
+		return;
+	}
+
+	if (pmd_huge(*pmdp)) {
+		format_pte(pmdp, pmd_val(*pmdp));
+		return;
+	}
+	printf("pmdp @ 0x%016lx = 0x%016lx\n", pmdp, pmd_val(*pmdp));
+
+	ptep = pte_offset_map(pmdp, addr);
+	if (pte_none(*ptep)) {
+		printf("no valid PTE\n");
+		return;
+	}
+
+	format_pte(ptep, pte_val(*ptep));
+
+	sync();
+	__delay(200);
+	catch_memory_errors = 0;
+}
+#else
+static void show_pte(unsigned long addr)
+{
+	printf("show_pte not yet implemented\n");
+}
+#endif /* CONFIG_PPC_BOOK3S_64 */
 
 static void show_tasks(void)
 {