Re: [PATCH v4] arm64/x86_64: show zero pfn information when using vtop

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Hi Kazu, lijiang
As lijiang mentioned in previous email, I add below comments into commit part: 

1. only supports displaying zero page for THP(except for 1G THP)
2. do not support for the hugetlb cases

And no changes in code.

-wrw

On 2023/5/29 19:55, Rongwei Wang wrote:

Now vtop can not show us the page is zero pfn
when PTE or PMD has attached ZERO PAGE. This
patch supports show this information directly
when using vtop, likes:

crash> vtop -c 13674 ffff8917e000
VIRTUAL     PHYSICAL
ffff8917e000  836e71000

PAGE DIRECTORY: ffff000802f8d000
    PGD: ffff000802f8dff8 => 884e29003
    PUD: ffff000844e29ff0 => 884e93003
    PMD: ffff000844e93240 => 840413003
    PTE: ffff000800413bf0 => 160000836e71fc3
   PAGE: 836e71000  (ZERO PAGE)
...

If huge page found:

crash> vtop -c 14538 ffff95800000
VIRTUAL     PHYSICAL
ffff95800000  910c00000

PAGE DIRECTORY: ffff000801fa0000
    PGD: ffff000801fa0ff8 => 884f53003
    PUD: ffff000844f53ff0 => 8426cb003
    PMD: ffff0008026cb560 => 60000910c00fc1
   PAGE: 910c00000  (2MB, ZERO PAGE)
...

That seems be sensible with this patch. And there
are two points have to be noted for 'ZERO PAGE'
label:
1. only supports displaying zero page for THP(except for 1G THP)
2. do not support for the hugetlb cases

Signed-off-by: Rongwei Wang <rongwei.wang@xxxxxxxxxxxxxxxxx>
---
  arm64.c  | 24 ++++++++++++++++--------
  defs.h   |  5 +++++
  memory.c | 23 +++++++++++++++++++++++
  x86_64.c |  9 +++++----
  4 files changed, 49 insertions(+), 12 deletions(-)

diff --git a/arm64.c b/arm64.c
index 56fb841..efbdccb 100644
--- a/arm64.c
+++ b/arm64.c
@@ -1787,7 +1787,8 @@ arm64_vtop_2level_64k(ulong pgd, ulong vaddr, physaddr_t *paddr, int verbose)
  	if ((pgd_val & PMD_TYPE_MASK) == PMD_TYPE_SECT) {
  		ulong sectionbase = (pgd_val & SECTION_PAGE_MASK_512MB) & PHYS_MASK;
  		if (verbose) {
-			fprintf(fp, "  PAGE: %lx  (512MB)\n\n", sectionbase);
+			fprintf(fp, "  PAGE: %lx  (512MB%s)\n\n", sectionbase,
+				IS_ZEROPAGE(sectionbase) ? ", ZERO PAGE" : "");
  			arm64_translate_pte(pgd_val, 0, 0);
  		}
  		*paddr = sectionbase + (vaddr & ~SECTION_PAGE_MASK_512MB);
@@ -1806,7 +1807,8 @@ arm64_vtop_2level_64k(ulong pgd, ulong vaddr, physaddr_t *paddr, int verbose)
  	if (pte_val & PTE_VALID) {
  		*paddr = (PAGEBASE(pte_val) & PHYS_MASK) + PAGEOFFSET(vaddr);
  		if (verbose) {
-			fprintf(fp, "  PAGE: %lx\n\n", PAGEBASE(*paddr));
+			fprintf(fp, "  PAGE: %lx  %s\n\n", PAGEBASE(*paddr),
+				IS_ZEROPAGE(PAGEBASE(*paddr)) ? "(ZERO PAGE)" : "");
  			arm64_translate_pte(pte_val, 0, 0);
  		}
  	} else {
@@ -1859,7 +1861,8 @@ arm64_vtop_3level_64k(ulong pgd, ulong vaddr, physaddr_t *paddr, int verbose)
  	if ((pmd_val & PMD_TYPE_MASK) == PMD_TYPE_SECT) {
  		ulong sectionbase = PTE_TO_PHYS(pmd_val) & SECTION_PAGE_MASK_512MB;
  		if (verbose) {
-			fprintf(fp, "  PAGE: %lx  (512MB)\n\n", sectionbase);
+			fprintf(fp, "  PAGE: %lx  (512MB%s)\n\n", sectionbase,
+				IS_ZEROPAGE(sectionbase) ? ", ZERO PAGE" : "");
  			arm64_translate_pte(pmd_val, 0, 0);
  		}
  		*paddr = sectionbase + (vaddr & ~SECTION_PAGE_MASK_512MB);
@@ -1878,7 +1881,8 @@ arm64_vtop_3level_64k(ulong pgd, ulong vaddr, physaddr_t *paddr, int verbose)
  	if (pte_val & PTE_VALID) {
  		*paddr = PTE_TO_PHYS(pte_val) + PAGEOFFSET(vaddr);
  		if (verbose) {
-			fprintf(fp, "  PAGE: %lx\n\n", PAGEBASE(*paddr));
+			fprintf(fp, "  PAGE: %lx  %s\n\n", PAGEBASE(*paddr),
+				IS_ZEROPAGE(PAGEBASE(*paddr)) ? "(ZERO PAGE)" : "");
  			arm64_translate_pte(pte_val, 0, 0);
  		}
  	} else {
@@ -1940,7 +1944,8 @@ arm64_vtop_3level_4k(ulong pgd, ulong vaddr, physaddr_t *paddr, int verbose)
  	if ((pmd_val & PMD_TYPE_MASK) == PMD_TYPE_SECT) {
  		ulong sectionbase = (pmd_val & SECTION_PAGE_MASK_2MB) & PHYS_MASK;
  		if (verbose) {
-			fprintf(fp, "  PAGE: %lx  (2MB)\n\n", sectionbase);
+			fprintf(fp, "  PAGE: %lx  (2MB%s)\n\n", sectionbase,
+				IS_ZEROPAGE(sectionbase) ? ", ZERO PAGE" : "");
  			arm64_translate_pte(pmd_val, 0, 0);
  		}
  		*paddr = sectionbase + (vaddr & ~SECTION_PAGE_MASK_2MB);
@@ -1959,7 +1964,8 @@ arm64_vtop_3level_4k(ulong pgd, ulong vaddr, physaddr_t *paddr, int verbose)
  	if (pte_val & PTE_VALID) {
  		*paddr = (PAGEBASE(pte_val) & PHYS_MASK) + PAGEOFFSET(vaddr);
  		if (verbose) {
-			fprintf(fp, "  PAGE: %lx\n\n", PAGEBASE(*paddr));
+			fprintf(fp, "  PAGE: %lx  %s\n\n", PAGEBASE(*paddr),
+				IS_ZEROPAGE(PAGEBASE(*paddr)) ? "(ZERO PAGE)" : "");
  			arm64_translate_pte(pte_val, 0, 0);
  		}
  	} else {
@@ -2029,7 +2035,8 @@ arm64_vtop_4level_4k(ulong pgd, ulong vaddr, physaddr_t *paddr, int verbose)
  	if ((pmd_val & PMD_TYPE_MASK) == PMD_TYPE_SECT) {
  		ulong sectionbase = (pmd_val & SECTION_PAGE_MASK_2MB) & PHYS_MASK;
  		if (verbose) {
-			fprintf(fp, "  PAGE: %lx  (2MB)\n\n", sectionbase);
+			fprintf(fp, "  PAGE: %lx  (2MB%s)\n\n", sectionbase,
+				IS_ZEROPAGE(sectionbase) ? ", ZERO PAGE" : "");
  			arm64_translate_pte(pmd_val, 0, 0);
  		}
  		*paddr = sectionbase + (vaddr & ~SECTION_PAGE_MASK_2MB);
@@ -2048,7 +2055,8 @@ arm64_vtop_4level_4k(ulong pgd, ulong vaddr, physaddr_t *paddr, int verbose)
  	if (pte_val & PTE_VALID) {
  		*paddr = (PAGEBASE(pte_val) & PHYS_MASK) + PAGEOFFSET(vaddr);
  		if (verbose) {
-			fprintf(fp, "  PAGE: %lx\n\n", PAGEBASE(*paddr));
+			fprintf(fp, "  PAGE: %lx  %s\n\n", PAGEBASE(*paddr),
+				IS_ZEROPAGE(PAGEBASE(*paddr)) ? "(ZERO PAGE)" : "");
  			arm64_translate_pte(pte_val, 0, 0);
  		}
  	} else {
diff --git a/defs.h b/defs.h
index 12ad6aa..a6e4ef3 100644
--- a/defs.h
+++ b/defs.h
@@ -2618,6 +2618,8 @@ struct vm_table {                /* kernel VM-related data */
  		char *name;
  	} *pageflags_data;
  	ulong max_mem_section_nr;
+	ulong zero_paddr;
+	ulong huge_zero_paddr;
  };
#define NODES (0x1) 
@@ -2999,6 +3001,9 @@ struct load_module {
  #define VIRTPAGEBASE(X)  (((ulong)(X)) & (ulong)machdep->pagemask)
  #define PHYSPAGEBASE(X)  (((physaddr_t)(X)) & (physaddr_t)machdep->pagemask)
+#define IS_ZEROPAGE(paddr) ((paddr) == vt->zero_paddr || \ 
+			      (paddr) == vt->huge_zero_paddr)
+
  /*
   * Sparse memory stuff
   *  These must follow the definitions in the kernel mmzone.h
diff --git a/memory.c b/memory.c
index 0568f18..d791283 100644
--- a/memory.c
+++ b/memory.c
@@ -1208,6 +1208,27 @@ vm_init(void)
  		machdep->memory_size()));
  	vt->paddr_prlen = strlen(buf);
+ vt->zero_paddr = ~0UL; 
+	if (kernel_symbol_exists("zero_pfn")) {
+		ulong zero_pfn;
+
+		if (readmem(symbol_value("zero_pfn"), KVADDR,
+			    &zero_pfn, sizeof(zero_pfn),
+			    "read zero_pfn", QUIET|RETURN_ON_ERROR))
+			vt->zero_paddr = zero_pfn << PAGESHIFT();
+	}
+
+	vt->huge_zero_paddr = ~0UL;
+	if (kernel_symbol_exists("huge_zero_pfn")) {
+		ulong huge_zero_pfn;
+
+		if (readmem(symbol_value("huge_zero_pfn"), KVADDR,
+			    &huge_zero_pfn, sizeof(huge_zero_pfn),
+			    "read huge_zero_pfn", QUIET|RETURN_ON_ERROR) &&
+		    huge_zero_pfn != ~0UL)
+			vt->huge_zero_paddr = huge_zero_pfn << PAGESHIFT();
+	}
+
  	if (vt->flags & PERCPU_KMALLOC_V1)
                  vt->dump_kmem_cache = dump_kmem_cache_percpu_v1;
  	else if (vt->flags & PERCPU_KMALLOC_V2)
@@ -14063,6 +14084,8 @@ dump_vm_table(int verbose)
  	} else {
  		fprintf(fp, "    node_online_map: (unused)\n");
  	}
+	fprintf(fp, "         zero_paddr: %lx\n", vt->zero_paddr);
+	fprintf(fp, "    huge_zero_paddr: %lx\n", vt->huge_zero_paddr);
  	fprintf(fp, "   nr_vm_stat_items: %d\n", vt->nr_vm_stat_items);
  	fprintf(fp, "      vm_stat_items: %s", (vt->flags & VM_STAT) ?
  		"\n" : "(not used)\n");
diff --git a/x86_64.c b/x86_64.c
index 5019c69..693a08b 100644
--- a/x86_64.c
+++ b/x86_64.c
@@ -2114,8 +2114,9 @@ x86_64_uvtop_level4(struct task_context *tc, ulong uvaddr, physaddr_t *paddr, in
  		goto no_upage;
          if (pmd_pte & _PAGE_PSE) {
  		if (verbose) {
-                        fprintf(fp, "  PAGE: %lx  (2MB)\n\n",
-				PAGEBASE(pmd_pte) & PHYSICAL_PAGE_MASK);
+			fprintf(fp, "  PAGE: %lx  (2MB%s)\n\n",
+				PAGEBASE(pmd_pte) & PHYSICAL_PAGE_MASK,
+				IS_ZEROPAGE(PAGEBASE(pmd_pte) & PHYSICAL_PAGE_MASK) ? ", ZERO PAGE" : "");
                          x86_64_translate_pte(pmd_pte, 0, 0);
                  }
@@ -2143,8 +2144,8 @@ x86_64_uvtop_level4(struct task_context *tc, ulong uvaddr, physaddr_t *paddr, in 
  	*paddr = (PAGEBASE(pte) & PHYSICAL_PAGE_MASK) + PAGEOFFSET(uvaddr);
if (verbose) { 
-		fprintf(fp, "  PAGE: %lx\n\n",
-			PAGEBASE(*paddr) & PHYSICAL_PAGE_MASK);
+		fprintf(fp, "  PAGE: %lx  %s\n\n", PAGEBASE(*paddr) & PHYSICAL_PAGE_MASK,
+			IS_ZEROPAGE(PAGEBASE(*paddr) & PHYSICAL_PAGE_MASK) ? "(ZERO PAGE)" : "");
  		x86_64_translate_pte(pte, 0, 0);
  	}


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