Re: [PATCH RFC] arm64: show zero pfn information when using vtop

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Hello,
Recently I handle some stuff about zero page with crash. I'm always use vtop to check
whether an virtual address has been set the zero page. But, it can not directly show whether a page 

is zero page or not. So I try to add this patch to support this.
And I'm not sure this idea is nice to be accepted, so just realize it on arm64 platform. I can finish others 

arch if it accepted.


Thanks for your time.

On 2023/5/1 00:02, 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)

       PTE        PHYSICAL   FLAGS
160000836e71fc3  836e71000  (VALID|USER|RDONLY|SHARED|AF|NG|PXN|UXN|SPECIAL)

       VMA           START       END     FLAGS FILE
ffff000844f51860 ffff8917c000 ffff8957d000 100073

       PAGE         PHYSICAL      MAPPING       INDEX CNT FLAGS
fffffe001fbb9c40  836e71000                0        0  1 2ffffc000001000 reserved

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)

      PTE        PHYSICAL   FLAGS
60000910c00fc1  910c00000  (VALID|USER|RDONLY|SHARED|AF|NG|PXN|UXN)

       VMA           START       END     FLAGS FILE
ffff0000caa711e0 ffff956a9000 ffff95aaa000 100073

       PAGE         PHYSICAL      MAPPING       INDEX CNT FLAGS
fffffe0023230000  910c00000                0        0  1 6ffffc000010000 head

That seems be sensible with this patch.

Signed-off-by: Rongwei Wang <rongwei.wang@xxxxxxxxxxxxxxxxx>
---
  arm64.c | 92 +++++++++++++++++++++++++++++++++++++++++++++++++++------
  defs.h  |  5 ++++
  2 files changed, 88 insertions(+), 9 deletions(-)

diff --git a/arm64.c b/arm64.c
index 56fb841..264572d 100644
--- a/arm64.c
+++ b/arm64.c
@@ -419,7 +419,25 @@ arm64_init(int when)
  		/* use machdep parameters */
  		arm64_calc_phys_offset();
  		arm64_calc_physvirt_offset();
-	
+
+		if (kernel_symbol_exists("zero_pfn")) {
+				ulong zero_pfn = 0;
+
+				if (readmem(symbol_value("zero_pfn"), KVADDR,
+					      &zero_pfn, sizeof(zero_pfn),
+					      "read zero_pfn", QUIET|RETURN_ON_ERROR))
+					machdep->zero_pfn = zero_pfn;
+		}
+
+		if (kernel_symbol_exists("huge_zero_pfn")) {
+				ulong huge_zero_pfn = 0;
+
+				if (readmem(symbol_value("huge_zero_pfn"), KVADDR,
+					      &huge_zero_pfn, sizeof(huge_zero_pfn),
+					      "read huge_zero_pfn", QUIET|RETURN_ON_ERROR))
+					machdep->huge_zero_pfn = huge_zero_pfn;
+		}
+
  		if (CRASHDEBUG(1)) {
  			if (machdep->flags & NEW_VMEMMAP)
  				fprintf(fp, "kimage_voffset: %lx\n",
@@ -1787,7 +1805,14 @@ 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);
+			if (kernel_symbol_exists("huge_zero_pfn")) {
+				if (sectionbase == (HUGE_ZEROPFN() << PAGESHIFT()))
+					fprintf(fp, "  PAGE: %lx  (512MB, ZERO PAGE)\n\n",
+						HUGE_ZEROPFN() << PAGESHIFT());
+				else
+					fprintf(fp, "  PAGE: %lx  (512MB)\n\n", sectionbase);
+			} else
+				fprintf(fp, "  PAGE: %lx  (512MB)\n\n", sectionbase);
  			arm64_translate_pte(pgd_val, 0, 0);
  		}
  		*paddr = sectionbase + (vaddr & ~SECTION_PAGE_MASK_512MB);
@@ -1806,7 +1831,14 @@ 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));
+			if (kernel_symbol_exists("zero_pfn")) {
+				if (PAGEBASE(*paddr) == (ZEROPFN() << PAGESHIFT()))
+					fprintf(fp, "  PAGE: %lx  (ZERO PAGE)\n\n",
+						ZEROPFN() << PAGESHIFT());
+				else
+					fprintf(fp, "  PAGE: %lx\n\n", PAGEBASE(*paddr));
+			} else
+				fprintf(fp, "  PAGE: %lx\n\n", PAGEBASE(*paddr));
  			arm64_translate_pte(pte_val, 0, 0);
  		}
  	} else {
@@ -1859,7 +1891,14 @@ 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);
+			if (kernel_symbol_exists("huge_zero_pfn")) {
+				if (sectionbase == (HUGE_ZEROPFN() << PAGESHIFT()))
+					fprintf(fp, "  PAGE: %lx  (512MB, ZERO PAGE)\n\n",
+						HUGE_ZEROPFN() << PAGESHIFT());
+				else
+					fprintf(fp, "  PAGE: %lx  (512MB)\n\n", sectionbase);
+			} else
+				fprintf(fp, "  PAGE: %lx  (512MB)\n\n", sectionbase);
  			arm64_translate_pte(pmd_val, 0, 0);
  		}
  		*paddr = sectionbase + (vaddr & ~SECTION_PAGE_MASK_512MB);
@@ -1878,7 +1917,14 @@ 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));
+			if (kernel_symbol_exists("zero_pfn")) {
+				if (PAGEBASE(*paddr) == (ZEROPFN() << PAGESHIFT()))
+					fprintf(fp, "  PAGE: %lx  (ZERO PAGE)\n\n",
+						ZEROPFN() << PAGESHIFT());
+				else
+					fprintf(fp, "  PAGE: %lx\n\n", PAGEBASE(*paddr));
+			} else
+				fprintf(fp, "  PAGE: %lx\n\n", PAGEBASE(*paddr));
  			arm64_translate_pte(pte_val, 0, 0);
  		}
  	} else {
@@ -1940,7 +1986,14 @@ 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);
+			if (kernel_symbol_exists("huge_zero_pfn")) {
+				if (sectionbase == (HUGE_ZEROPFN() << PAGESHIFT()))
+					fprintf(fp, "  PAGE: %lx  (2MB, ZERO PAGE)\n\n",
+						HUGE_ZEROPFN() << PAGESHIFT());
+				else
+					fprintf(fp, "  PAGE: %lx  (2MB)\n\n", sectionbase);
+			} else
+				fprintf(fp, "  PAGE: %lx  (2MB)\n\n", sectionbase);
  			arm64_translate_pte(pmd_val, 0, 0);
  		}
  		*paddr = sectionbase + (vaddr & ~SECTION_PAGE_MASK_2MB);
@@ -1959,7 +2012,14 @@ 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));
+			if (kernel_symbol_exists("zero_pfn")) {
+				if (PAGEBASE(*paddr) == (ZEROPFN() << PAGESHIFT()))
+					fprintf(fp, "  PAGE: %lx  (ZERO PAGE)\n\n",
+						ZEROPFN() << PAGESHIFT());
+				else
+					fprintf(fp, "  PAGE: %lx\n\n", PAGEBASE(*paddr));
+			} else
+				fprintf(fp, "  PAGE: %lx\n\n", PAGEBASE(*paddr));
  			arm64_translate_pte(pte_val, 0, 0);
  		}
  	} else {
@@ -2029,7 +2089,14 @@ 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);
+			if (kernel_symbol_exists("huge_zero_pfn")) {
+				if (sectionbase == (HUGE_ZEROPFN() << PAGESHIFT()))
+					fprintf(fp, "  PAGE: %lx  (2MB, ZERO PAGE)\n\n",
+						HUGE_ZEROPFN() << PAGESHIFT());
+				else
+					fprintf(fp, "  PAGE: %lx  (2MB)\n\n", sectionbase);
+			} else
+				fprintf(fp, "  PAGE: %lx  (2MB)\n\n", sectionbase);
  			arm64_translate_pte(pmd_val, 0, 0);
  		}
  		*paddr = sectionbase + (vaddr & ~SECTION_PAGE_MASK_2MB);
@@ -2048,7 +2115,14 @@ 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));
+			if (kernel_symbol_exists("zero_pfn")) {
+				if (PAGEBASE(*paddr) == (ZEROPFN() << PAGESHIFT()))
+					fprintf(fp, "  PAGE: %lx  (ZERO PAGE)\n\n",
+						ZEROPFN() << PAGESHIFT());
+				else
+					fprintf(fp, "  PAGE: %lx\n\n", PAGEBASE(*paddr));
+			} else
+				fprintf(fp, "  PAGE: %lx\n\n", PAGEBASE(*paddr));
  			arm64_translate_pte(pte_val, 0, 0);
  		}
  	} else {
diff --git a/defs.h b/defs.h
index 12ad6aa..4ed2d0a 100644
--- a/defs.h
+++ b/defs.h
@@ -1071,6 +1071,8 @@ struct machdep_table {
          void (*show_interrupts)(int, ulong *);
  	int (*is_page_ptr)(ulong, physaddr_t *);
  	int (*get_cpu_reg)(int, int, const char *, int, void *);
+	ulong zero_pfn;
+	ulong huge_zero_pfn;
  };
/* 
@@ -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 ZEROPFN() (machdep->zero_pfn) 
+#define HUGE_ZEROPFN()   (machdep->huge_zero_pfn)
+
  /*
   * Sparse memory stuff
   *  These must follow the definitions in the kernel mmzone.h


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