+ mm-sparse-add-vmemmap__hvo-functions.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/sparse: add vmemmap_*_hvo functions
has been added to the -mm mm-unstable branch.  Its filename is
     mm-sparse-add-vmemmap__hvo-functions.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-sparse-add-vmemmap__hvo-functions.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Before you just go and hit "reply", please:
   a) Consider who else should be cc'ed
   b) Prefer to cc a suitable mailing list as well
   c) Ideally: find the original patch on the mailing list and do a
      reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: Frank van der Linden <fvdl@google.com>
Subject: mm/sparse: add vmemmap_*_hvo functions
Date: Wed, 29 Jan 2025 22:41:44 +0000

Add a few functions to enable early HVO:

vmemmap_populate_hvo
vmemmap_undo_hvo
vmemmap_wrprotect_hvo

The populate and undo functions are expected to be used in early init,
from the sparse_init_nid_early() function.  The wrprotect function is to
be used, potentially, later.

To implement these functions, mostly re-use the existing compound pages
vmemmap logic used by DAX.  vmemmap_populate_address has its argument
changed a bit in this commit: the page structure passed in to be reused in
the mapping is replaced by a PFN and a flag.  The flag indicates whether
an extra ref should be taken on the vmemmap page containing the head page
structure.  Taking the ref is appropriate to for DAX / ZONE_DEVICE, but
not for HugeTLB HVO.

The HugeTLB vmemmap optimization maps tail page structure pages read-only.
The vmemmap_wrprotect_hvo function that does this is implemented
separately, because it cannot be guaranteed that reserved page structures
will not be write accessed during memory initialization.  Even with
CONFIG_DEFERRED_STRUCT_PAGE_INIT, they might still be written to (if they
are at the bottom of a zone).  So, vmemmap_populate_hvo leaves the tail
page structure pages RW initially, and then later during initialization,
after memmap init is fully done, vmemmap_wrprotect_hvo must be called to
finish the job.

Subsequent commits will use these functions for early HugeTLB HVO.

Link: https://lkml.kernel.org/r/20250129224157.2046079-16-fvdl@google.com
Signed-off-by: Frank van der Linden <fvdl@google.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Joao Martins <joao.m.martins@oracle.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Roman Gushchin (Cruise) <roman.gushchin@linux.dev>
Cc: Usama Arif <usamaarif642@gmail.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Zhenguo Yao <yaozhenguo1@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/mm.h  |    9 ++
 mm/sparse-vmemmap.c |  141 +++++++++++++++++++++++++++++++++++++-----
 2 files changed, 135 insertions(+), 15 deletions(-)

--- a/include/linux/mm.h~mm-sparse-add-vmemmap__hvo-functions
+++ a/include/linux/mm.h
@@ -3837,7 +3837,8 @@ p4d_t *vmemmap_p4d_populate(pgd_t *pgd,
 pud_t *vmemmap_pud_populate(p4d_t *p4d, unsigned long addr, int node);
 pmd_t *vmemmap_pmd_populate(pud_t *pud, unsigned long addr, int node);
 pte_t *vmemmap_pte_populate(pmd_t *pmd, unsigned long addr, int node,
-			    struct vmem_altmap *altmap, struct page *reuse);
+			    struct vmem_altmap *altmap, unsigned long ptpfn,
+			    unsigned long flags);
 void *vmemmap_alloc_block(unsigned long size, int node);
 struct vmem_altmap;
 void *vmemmap_alloc_block_buf(unsigned long size, int node,
@@ -3853,6 +3854,12 @@ int vmemmap_populate_hugepages(unsigned
 			       int node, struct vmem_altmap *altmap);
 int vmemmap_populate(unsigned long start, unsigned long end, int node,
 		struct vmem_altmap *altmap);
+int vmemmap_populate_hvo(unsigned long start, unsigned long end, int node,
+			 unsigned long headsize);
+int vmemmap_undo_hvo(unsigned long start, unsigned long end, int node,
+		     unsigned long headsize);
+void vmemmap_wrprotect_hvo(unsigned long start, unsigned long end, int node,
+			  unsigned long headsize);
 void vmemmap_populate_print_last(void);
 #ifdef CONFIG_MEMORY_HOTPLUG
 void vmemmap_free(unsigned long start, unsigned long end,
--- a/mm/sparse-vmemmap.c~mm-sparse-add-vmemmap__hvo-functions
+++ a/mm/sparse-vmemmap.c
@@ -30,6 +30,13 @@
 
 #include <asm/dma.h>
 #include <asm/pgalloc.h>
+#include <asm/tlbflush.h>
+
+/*
+ * Flags for vmemmap_populate_range and friends.
+ */
+/* Get a ref on the head page struct page, for ZONE_DEVICE compound pages */
+#define VMEMMAP_POPULATE_PAGEREF	0x0001
 
 #include "internal.h"
 
@@ -144,17 +151,18 @@ void __meminit vmemmap_verify(pte_t *pte
 
 pte_t * __meminit vmemmap_pte_populate(pmd_t *pmd, unsigned long addr, int node,
 				       struct vmem_altmap *altmap,
-				       struct page *reuse)
+				       unsigned long ptpfn, unsigned long flags)
 {
 	pte_t *pte = pte_offset_kernel(pmd, addr);
 	if (pte_none(ptep_get(pte))) {
 		pte_t entry;
 		void *p;
 
-		if (!reuse) {
+		if (!ptpfn) {
 			p = vmemmap_alloc_block_buf(PAGE_SIZE, node, altmap);
 			if (!p)
 				return NULL;
+			ptpfn = PHYS_PFN(__pa(p));
 		} else {
 			/*
 			 * When a PTE/PMD entry is freed from the init_mm
@@ -165,10 +173,10 @@ pte_t * __meminit vmemmap_pte_populate(p
 			 * and through vmemmap_populate_compound_pages() when
 			 * slab is available.
 			 */
-			get_page(reuse);
-			p = page_to_virt(reuse);
+			if (flags & VMEMMAP_POPULATE_PAGEREF)
+				get_page(pfn_to_page(ptpfn));
 		}
-		entry = pfn_pte(__pa(p) >> PAGE_SHIFT, PAGE_KERNEL);
+		entry = pfn_pte(ptpfn, PAGE_KERNEL);
 		set_pte_at(&init_mm, addr, pte, entry);
 	}
 	return pte;
@@ -238,7 +246,8 @@ pgd_t * __meminit vmemmap_pgd_populate(u
 
 static pte_t * __meminit vmemmap_populate_address(unsigned long addr, int node,
 					      struct vmem_altmap *altmap,
-					      struct page *reuse)
+					      unsigned long ptpfn,
+					      unsigned long flags)
 {
 	pgd_t *pgd;
 	p4d_t *p4d;
@@ -258,7 +267,7 @@ static pte_t * __meminit vmemmap_populat
 	pmd = vmemmap_pmd_populate(pud, addr, node);
 	if (!pmd)
 		return NULL;
-	pte = vmemmap_pte_populate(pmd, addr, node, altmap, reuse);
+	pte = vmemmap_pte_populate(pmd, addr, node, altmap, ptpfn, flags);
 	if (!pte)
 		return NULL;
 	vmemmap_verify(pte, node, addr, addr + PAGE_SIZE);
@@ -269,13 +278,15 @@ static pte_t * __meminit vmemmap_populat
 static int __meminit vmemmap_populate_range(unsigned long start,
 					    unsigned long end, int node,
 					    struct vmem_altmap *altmap,
-					    struct page *reuse)
+					    unsigned long ptpfn,
+					    unsigned long flags)
 {
 	unsigned long addr = start;
 	pte_t *pte;
 
 	for (; addr < end; addr += PAGE_SIZE) {
-		pte = vmemmap_populate_address(addr, node, altmap, reuse);
+		pte = vmemmap_populate_address(addr, node, altmap,
+					       ptpfn, flags);
 		if (!pte)
 			return -ENOMEM;
 	}
@@ -286,7 +297,107 @@ static int __meminit vmemmap_populate_ra
 int __meminit vmemmap_populate_basepages(unsigned long start, unsigned long end,
 					 int node, struct vmem_altmap *altmap)
 {
-	return vmemmap_populate_range(start, end, node, altmap, NULL);
+	return vmemmap_populate_range(start, end, node, altmap, 0, 0);
+}
+
+/*
+ * Undo populate_hvo, and replace it with a normal base page mapping.
+ * Used in memory init in case a HVO mapping needs to be undone.
+ *
+ * This can happen when it is discovered that a memblock allocated
+ * hugetlb page spans multiple zones, which can only be verified
+ * after zones have been initialized.
+ *
+ * We know that:
+ * 1) The first @headsize / PAGE_SIZE vmemmap pages were individually
+ *    allocated through memblock, and mapped.
+ *
+ * 2) The rest of the vmemmap pages are mirrors of the last head page.
+ */
+int __meminit vmemmap_undo_hvo(unsigned long addr, unsigned long end,
+				      int node, unsigned long headsize)
+{
+	unsigned long maddr, pfn;
+	pte_t *pte;
+	int headpages;
+
+	/*
+	 * Should only be called early in boot, so nothing will
+	 * be accessing these page structures.
+	 */
+	WARN_ON(!early_boot_irqs_disabled);
+
+	headpages = headsize >> PAGE_SHIFT;
+
+	/*
+	 * Clear mirrored mappings for tail page structs.
+	 */
+	for (maddr = addr + headsize; maddr < end; maddr += PAGE_SIZE) {
+		pte = virt_to_kpte(maddr);
+		pte_clear(&init_mm, maddr, pte);
+	}
+
+	/*
+	 * Clear and free mappings for head page and first tail page
+	 * structs.
+	 */
+	for (maddr = addr; headpages-- > 0; maddr += PAGE_SIZE) {
+		pte = virt_to_kpte(maddr);
+		pfn = pte_pfn(ptep_get(pte));
+		pte_clear(&init_mm, maddr, pte);
+		memblock_phys_free(PFN_PHYS(pfn), PAGE_SIZE);
+	}
+
+	flush_tlb_kernel_range(addr, end);
+
+	return vmemmap_populate(addr, end, node, NULL);
+}
+
+/*
+ * Write protect the mirrored tail page structs for HVO. This will be
+ * called from the hugetlb code when gathering and initializing the
+ * memblock allocated gigantic pages. The write protect can't be
+ * done earlier, since it can't be guaranteed that the reserved
+ * page structures will not be written to during initialization,
+ * even if CONFIG_DEFERRED_STRUCT_PAGE_INIT is enabled.
+ *
+ * The PTEs are known to exist, and nothing else should be touching
+ * these pages. The caller is responsible for any TLB flushing.
+ */
+void vmemmap_wrprotect_hvo(unsigned long addr, unsigned long end,
+				    int node, unsigned long headsize)
+{
+	unsigned long maddr;
+	pte_t *pte;
+
+	for (maddr = addr + headsize; maddr < end; maddr += PAGE_SIZE) {
+		pte = virt_to_kpte(maddr);
+		ptep_set_wrprotect(&init_mm, maddr, pte);
+	}
+}
+
+/*
+ * Populate vmemmap pages HVO-style. The first page contains the head
+ * page and needed tail pages, the other ones are mirrors of the first
+ * page.
+ */
+int __meminit vmemmap_populate_hvo(unsigned long addr, unsigned long end,
+				       int node, unsigned long headsize)
+{
+	pte_t *pte;
+	unsigned long maddr;
+
+	for (maddr = addr; maddr < addr + headsize; maddr += PAGE_SIZE) {
+		pte = vmemmap_populate_address(maddr, node, NULL, 0, 0);
+		if (!pte)
+			return -ENOMEM;
+	}
+
+	/*
+	 * Reuse the last page struct page mapped above for the rest.
+	 */
+	return vmemmap_populate_range(maddr, end, node, NULL,
+					pte_pfn(ptep_get(pte)), 0);
 }
 
 void __weak __meminit vmemmap_set_pmd(pmd_t *pmd, void *p, int node,
@@ -409,7 +520,8 @@ static int __meminit vmemmap_populate_co
 		 * with just tail struct pages.
 		 */
 		return vmemmap_populate_range(start, end, node, NULL,
-					      pte_page(ptep_get(pte)));
+					      pte_pfn(ptep_get(pte)),
+					      VMEMMAP_POPULATE_PAGEREF);
 	}
 
 	size = min(end - start, pgmap_vmemmap_nr(pgmap) * sizeof(struct page));
@@ -417,13 +529,13 @@ static int __meminit vmemmap_populate_co
 		unsigned long next, last = addr + size;
 
 		/* Populate the head page vmemmap page */
-		pte = vmemmap_populate_address(addr, node, NULL, NULL);
+		pte = vmemmap_populate_address(addr, node, NULL, 0, 0);
 		if (!pte)
 			return -ENOMEM;
 
 		/* Populate the tail pages vmemmap page */
 		next = addr + PAGE_SIZE;
-		pte = vmemmap_populate_address(next, node, NULL, NULL);
+		pte = vmemmap_populate_address(next, node, NULL, 0, 0);
 		if (!pte)
 			return -ENOMEM;
 
@@ -433,7 +545,8 @@ static int __meminit vmemmap_populate_co
 		 */
 		next += PAGE_SIZE;
 		rc = vmemmap_populate_range(next, last, node, NULL,
-					    pte_page(ptep_get(pte)));
+					    pte_pfn(ptep_get(pte)),
+					    VMEMMAP_POPULATE_PAGEREF);
 		if (rc)
 			return -ENOMEM;
 	}
_

Patches currently in -mm which might be from fvdl@google.com are

mm-cma-export-total-and-free-number-of-pages-for-cma-areas.patch
mm-cma-support-multiple-contiguous-ranges-if-requested.patch
mm-cma-introduce-cma_intersects-function.patch
mm-hugetlb-use-cma_declare_contiguous_multi.patch
mm-hugetlb-fix-round-robin-bootmem-allocation.patch
mm-hugetlb-remove-redundant-__clearpagereserved.patch
mm-hugetlb-use-online-nodes-for-bootmem-allocation.patch
mm-hugetlb-convert-cmdline-parameters-from-setup-to-early.patch
x86-mm-make-register_page_bootmem_memmap-handle-pte-mappings.patch
mm-bootmem_info-export-register_page_bootmem_memmap.patch
mm-sparse-allow-for-alternate-vmemmap-section-init-at-boot.patch
mm-hugetlb-set-migratetype-for-bootmem-folios.patch
mm-define-__init_reserved_page_zone-function.patch
mm-hugetlb-check-bootmem-pages-for-zone-intersections.patch
mm-sparse-add-vmemmap__hvo-functions.patch
mm-hugetlb-deal-with-multiple-calls-to-hugetlb_bootmem_alloc.patch
mm-hugetlb-move-huge_boot_pages-list-init-to-hugetlb_bootmem_alloc.patch
mm-hugetlb-add-pre-hvo-framework.patch
mm-hugetlb_vmemmap-fix-hugetlb_vmemmap_restore_folios-definition.patch
mm-hugetlb-do-pre-hvo-for-bootmem-allocated-pages.patch
x86-setup-call-hugetlb_bootmem_alloc-early.patch
x86-mm-set-arch_want_sparsemem_vmemmap_preinit.patch
mm-cma-simplify-zone-intersection-check.patch
mm-cma-introduce-a-cma-validate-function.patch
mm-cma-introduce-interface-for-early-reservations.patch
mm-hugetlb-add-hugetlb_cma_only-cmdline-option.patch
mm-hugetlb-enable-bootmem-allocation-from-cma-areas.patch
mm-hugetlb-move-hugetlb-cma-code-in-to-its-own-file.patch