* Re: [PATCH] x86/mm: fix freeing of PMD-sized vmemmap pages
2026-04-28 10:29 [PATCH] x86/mm: fix freeing of PMD-sized vmemmap pages David Hildenbrand (Arm)
@ 2026-04-28 10:34 ` David Hildenbrand (Arm)
2026-04-28 13:20 ` Lance Yang
` (2 subsequent siblings)
3 siblings, 0 replies; 8+ messages in thread
From: David Hildenbrand (Arm) @ 2026-04-28 10:34 UTC (permalink / raw)
To: Dave Hansen, Andy Lutomirski, Peter Zijlstra, Thomas Gleixner,
Ingo Molnar, Borislav Petkov, x86, H. Peter Anvin,
Mike Rapoport (Microsoft), Jason Gunthorpe, Lu Baolu,
Andrew Morton
Cc: linux-kernel, linux-mm, stable
>
> -static void __meminit free_hugepage_table(struct page *page,
> +static void __meminit free_vmemmap_pages(struct page *page, unsigned int order,
> struct vmem_altmap *altmap)
> {
> - if (altmap)
> - vmem_altmap_free(altmap, PMD_SIZE / PAGE_SIZE);
> - else
> - free_pagetable(page, get_order(PMD_SIZE));
> + if (altmap) {
> + vmem_altmap_free(altmap, 1u << order);
> + } else if (PageReserved(page)) {
> + unsigned long nr_pages = 1 << order;
Staring at this code again, I should move that up so I can reuse it in the
vmem_altmap_free() call.
--
Cheers,
David
^ permalink raw reply [flat|nested] 8+ messages in thread* Re: [PATCH] x86/mm: fix freeing of PMD-sized vmemmap pages
2026-04-28 10:29 [PATCH] x86/mm: fix freeing of PMD-sized vmemmap pages David Hildenbrand (Arm)
2026-04-28 10:34 ` David Hildenbrand (Arm)
@ 2026-04-28 13:20 ` Lance Yang
2026-04-28 19:36 ` David Hildenbrand (Arm)
2026-04-28 20:47 ` Mike Rapoport
2026-04-29 2:12 ` Lance Yang
3 siblings, 1 reply; 8+ messages in thread
From: Lance Yang @ 2026-04-28 13:20 UTC (permalink / raw)
To: david
Cc: dave.hansen, luto, peterz, tglx, mingo, bp, x86, hpa, rppt, jgg,
baolu.lu, akpm, linux-kernel, linux-mm, stable, Lance Yang
On Tue, Apr 28, 2026 at 12:29:36PM +0200, David Hildenbrand (Arm) wrote:
>In commit bf9e4e30f353 ("x86/mm: use pagetable_free()"), we switched
>from freeing non-boot page tables through __free_pages() to
>pagetable_free().
>
>However, the function is also called to free vmemmap pages.
>
>Given that vmemmap pages are not page tables, already the page_ptdesc(page)
>is wrong. But worse, pagetable_free() calls
>
> __free_pages(page, compound_order(page));
>
>As vmemmap pages are not compound pages (see vmemmap_alloc_block()) --
>except for HVO, which doesn't apply here -- we will only free the first
>page when freeing a PMD-sized vmemmap page, leaking the other ones.
>
>Fix it by properly decoupling pagetable and vmemmap freeing.
>free_pagetable() no longer has to mess with SECTION_INFO, as only the
>vmemmap is marked like that in register_page_bootmem_memmap().
>
>While at it, just wire up the altmap parameter for remove_pte_table().
>Also, the indentation in remove_pmd_table() is messed up, let's fix that
>while touching it.
>
>Note that we'll try to get rid of that bootmem info handling soon. For
>now, we'll handle it similar to free_pagetable(), just avoiding the
>ifdef.
>
>Fixes: bf9e4e30f353 ("x86/mm: use pagetable_free()")
>Cc: stable@vger.kernel.org
>Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
>---
>Reproduced and tested with a simple VM with a virtio-mem device,
>repeatedly adding and removing memory.
>
>Found by code inspection while working on bootmem_info removal.
>---
Cool! I just reproduced the leak with QEMU pc-dimm memory hotplug as
well.
Without the fix, nr_free_pages kept dropping after the hotplugged memory
was removed again. With the fix applied, it stays stable over repeated
add/remove cycles :)
Tested-by: Lance Yang <lance.yang@linux.dev>
^ permalink raw reply [flat|nested] 8+ messages in thread* Re: [PATCH] x86/mm: fix freeing of PMD-sized vmemmap pages
2026-04-28 13:20 ` Lance Yang
@ 2026-04-28 19:36 ` David Hildenbrand (Arm)
0 siblings, 0 replies; 8+ messages in thread
From: David Hildenbrand (Arm) @ 2026-04-28 19:36 UTC (permalink / raw)
To: Lance Yang
Cc: dave.hansen, luto, peterz, tglx, mingo, bp, x86, hpa, rppt, jgg,
baolu.lu, akpm, linux-kernel, linux-mm, stable
On 4/28/26 15:20, Lance Yang wrote:
>
> On Tue, Apr 28, 2026 at 12:29:36PM +0200, David Hildenbrand (Arm) wrote:
>> In commit bf9e4e30f353 ("x86/mm: use pagetable_free()"), we switched
>>from freeing non-boot page tables through __free_pages() to
>> pagetable_free().
>>
>> However, the function is also called to free vmemmap pages.
>>
>> Given that vmemmap pages are not page tables, already the page_ptdesc(page)
>> is wrong. But worse, pagetable_free() calls
>>
>> __free_pages(page, compound_order(page));
>>
>> As vmemmap pages are not compound pages (see vmemmap_alloc_block()) --
>> except for HVO, which doesn't apply here -- we will only free the first
>> page when freeing a PMD-sized vmemmap page, leaking the other ones.
>>
>> Fix it by properly decoupling pagetable and vmemmap freeing.
>> free_pagetable() no longer has to mess with SECTION_INFO, as only the
>> vmemmap is marked like that in register_page_bootmem_memmap().
>>
>> While at it, just wire up the altmap parameter for remove_pte_table().
>> Also, the indentation in remove_pmd_table() is messed up, let's fix that
>> while touching it.
>>
>> Note that we'll try to get rid of that bootmem info handling soon. For
>> now, we'll handle it similar to free_pagetable(), just avoiding the
>> ifdef.
>>
>> Fixes: bf9e4e30f353 ("x86/mm: use pagetable_free()")
>> Cc: stable@vger.kernel.org
>> Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
>> ---
>> Reproduced and tested with a simple VM with a virtio-mem device,
>> repeatedly adding and removing memory.
>>
>> Found by code inspection while working on bootmem_info removal.
>> ---
>
> Cool! I just reproduced the leak with QEMU pc-dimm memory hotplug as
> well.
>
> Without the fix, nr_free_pages kept dropping after the hotplugged memory
> was removed again. With the fix applied, it stays stable over repeated
> add/remove cycles :)
>
> Tested-by: Lance Yang <lance.yang@linux.dev>
Thanks Lance! I'll wait a bit more for feedback, and then resend v2 with the
"nr_pages" simplification.
--
Cheers,
David
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH] x86/mm: fix freeing of PMD-sized vmemmap pages
2026-04-28 10:29 [PATCH] x86/mm: fix freeing of PMD-sized vmemmap pages David Hildenbrand (Arm)
2026-04-28 10:34 ` David Hildenbrand (Arm)
2026-04-28 13:20 ` Lance Yang
@ 2026-04-28 20:47 ` Mike Rapoport
2026-04-29 2:12 ` Lance Yang
3 siblings, 0 replies; 8+ messages in thread
From: Mike Rapoport @ 2026-04-28 20:47 UTC (permalink / raw)
To: David Hildenbrand (Arm)
Cc: Dave Hansen, Andy Lutomirski, Peter Zijlstra, Thomas Gleixner,
Ingo Molnar, Borislav Petkov, x86, H. Peter Anvin,
Jason Gunthorpe, Lu Baolu, Andrew Morton, linux-kernel, linux-mm,
stable
On Tue, Apr 28, 2026 at 12:29:36PM +0200, David Hildenbrand (Arm) wrote:
> In commit bf9e4e30f353 ("x86/mm: use pagetable_free()"), we switched
> from freeing non-boot page tables through __free_pages() to
> pagetable_free().
>
> However, the function is also called to free vmemmap pages.
>
> Given that vmemmap pages are not page tables, already the page_ptdesc(page)
> is wrong. But worse, pagetable_free() calls
>
> __free_pages(page, compound_order(page));
>
> As vmemmap pages are not compound pages (see vmemmap_alloc_block()) --
> except for HVO, which doesn't apply here -- we will only free the first
> page when freeing a PMD-sized vmemmap page, leaking the other ones.
>
> Fix it by properly decoupling pagetable and vmemmap freeing.
> free_pagetable() no longer has to mess with SECTION_INFO, as only the
> vmemmap is marked like that in register_page_bootmem_memmap().
>
> While at it, just wire up the altmap parameter for remove_pte_table().
> Also, the indentation in remove_pmd_table() is messed up, let's fix that
> while touching it.
>
> Note that we'll try to get rid of that bootmem info handling soon. For
> now, we'll handle it similar to free_pagetable(), just avoiding the
> ifdef.
>
> Fixes: bf9e4e30f353 ("x86/mm: use pagetable_free()")
> Cc: stable@vger.kernel.org
> Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> ---
> Reproduced and tested with a simple VM with a virtio-mem device,
> repeatedly adding and removing memory.
>
> Found by code inspection while working on bootmem_info removal.
> ---
> arch/x86/mm/init_64.c | 43 +++++++++++++++++++++++++++----------------
> 1 file changed, 27 insertions(+), 16 deletions(-)
>
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index df2261fa4f98..8d03e44a7fb9 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -1014,7 +1014,7 @@ static void __meminit free_pagetable(struct page *page, int order)
> #ifdef CONFIG_HAVE_BOOTMEM_INFO_NODE
> enum bootmem_type type = bootmem_type(page);
>
> - if (type == SECTION_INFO || type == MIX_SECTION_INFO) {
> + if (type == MIX_SECTION_INFO) {
> while (nr_pages--)
> put_page_bootmem(page++);
> } else {
> @@ -1028,13 +1028,24 @@ static void __meminit free_pagetable(struct page *page, int order)
> }
> }
>
> -static void __meminit free_hugepage_table(struct page *page,
> +static void __meminit free_vmemmap_pages(struct page *page, unsigned int order,
> struct vmem_altmap *altmap)
> {
> - if (altmap)
> - vmem_altmap_free(altmap, PMD_SIZE / PAGE_SIZE);
> - else
> - free_pagetable(page, get_order(PMD_SIZE));
> + if (altmap) {
> + vmem_altmap_free(altmap, 1u << order);
> + } else if (PageReserved(page)) {
> + unsigned long nr_pages = 1 << order;
> +
> + if (IS_ENABLED(CONFIG_HAVE_BOOTMEM_INFO_NODE) &&
> + bootmem_type(page) == SECTION_INFO) {
> + while (nr_pages--)
> + put_page_bootmem(page++);
> + } else {
> + free_reserved_pages(page, nr_pages);
> + }
> + } else {
> + __free_pages(page, order);
> + }
> }
>
> static void __meminit free_pte_table(pte_t *pte_start, pmd_t *pmd)
> @@ -1093,7 +1104,7 @@ static void __meminit free_pud_table(pud_t *pud_start, p4d_t *p4d)
>
> static void __meminit
> remove_pte_table(pte_t *pte_start, unsigned long addr, unsigned long end,
> - bool direct)
> + bool direct, struct vmem_altmap *altmap)
> {
> unsigned long next, pages = 0;
> pte_t *pte;
> @@ -1118,7 +1129,7 @@ remove_pte_table(pte_t *pte_start, unsigned long addr, unsigned long end,
> return;
>
> if (!direct)
> - free_pagetable(pte_page(*pte), 0);
> + free_vmemmap_pages(pte_page(*pte), 0, altmap);
>
> spin_lock(&init_mm.page_table_lock);
> pte_clear(&init_mm, addr, pte);
> @@ -1153,25 +1164,25 @@ remove_pmd_table(pmd_t *pmd_start, unsigned long addr, unsigned long end,
> if (IS_ALIGNED(addr, PMD_SIZE) &&
> IS_ALIGNED(next, PMD_SIZE)) {
> if (!direct)
> - free_hugepage_table(pmd_page(*pmd),
> - altmap);
> + free_vmemmap_pages(pmd_page(*pmd),
> + PMD_ORDER, altmap);
>
> spin_lock(&init_mm.page_table_lock);
> pmd_clear(pmd);
> spin_unlock(&init_mm.page_table_lock);
> pages++;
> } else if (vmemmap_pmd_is_unused(addr, next)) {
> - free_hugepage_table(pmd_page(*pmd),
> - altmap);
> - spin_lock(&init_mm.page_table_lock);
> - pmd_clear(pmd);
> - spin_unlock(&init_mm.page_table_lock);
> + free_vmemmap_pages(pmd_page(*pmd), PMD_ORDER,
> + altmap);
> + spin_lock(&init_mm.page_table_lock);
> + pmd_clear(pmd);
> + spin_unlock(&init_mm.page_table_lock);
> }
> continue;
> }
>
> pte_base = (pte_t *)pmd_page_vaddr(*pmd);
> - remove_pte_table(pte_base, addr, next, direct);
> + remove_pte_table(pte_base, addr, next, direct, altmap);
> free_pte_table(pte_base, pmd);
> }
>
>
> ---
>
> base-commit: a2ddbfd1af0f54ea84bf17f0400088815d012e8d
>
> change-id: 20260428-vmemmap-ab4b949aa727
>
> --
>
> Cheers,
>
> David
>
--
Sincerely yours,
Mike.
^ permalink raw reply [flat|nested] 8+ messages in thread* Re: [PATCH] x86/mm: fix freeing of PMD-sized vmemmap pages
2026-04-28 10:29 [PATCH] x86/mm: fix freeing of PMD-sized vmemmap pages David Hildenbrand (Arm)
` (2 preceding siblings ...)
2026-04-28 20:47 ` Mike Rapoport
@ 2026-04-29 2:12 ` Lance Yang
2026-04-29 2:30 ` Lance Yang
2026-04-29 5:50 ` David Hildenbrand (Arm)
3 siblings, 2 replies; 8+ messages in thread
From: Lance Yang @ 2026-04-29 2:12 UTC (permalink / raw)
To: david
Cc: dave.hansen, luto, peterz, tglx, mingo, bp, x86, hpa, rppt, jgg,
baolu.lu, akpm, linux-kernel, linux-mm, stable, Lance Yang
On Tue, Apr 28, 2026 at 12:29:36PM +0200, David Hildenbrand (Arm) wrote:
>In commit bf9e4e30f353 ("x86/mm: use pagetable_free()"), we switched
>from freeing non-boot page tables through __free_pages() to
>pagetable_free().
>
>However, the function is also called to free vmemmap pages.
>
>Given that vmemmap pages are not page tables, already the page_ptdesc(page)
>is wrong. But worse, pagetable_free() calls
>
> __free_pages(page, compound_order(page));
>
>As vmemmap pages are not compound pages (see vmemmap_alloc_block()) --
>except for HVO, which doesn't apply here -- we will only free the first
>page when freeing a PMD-sized vmemmap page, leaking the other ones.
>
>Fix it by properly decoupling pagetable and vmemmap freeing.
>free_pagetable() no longer has to mess with SECTION_INFO, as only the
>vmemmap is marked like that in register_page_bootmem_memmap().
>
>While at it, just wire up the altmap parameter for remove_pte_table().
>Also, the indentation in remove_pmd_table() is messed up, let's fix that
>while touching it.
One thing I'm not sure about is passing altmap down into
remove_pte_table().
Do we actually know that a non-NULL altmap means that the vmemmap
backing page came from that altmap?
On x86 we still have in vmemmap_populate():
if (end - start < PAGES_PER_SECTION * sizeof(struct page))
err = vmemmap_populate_basepages(start, end, node, NULL);
So for smaller-than-section vmemmap ranges, even if the caller has an
altmap, the backing pages are allocated from normal memory. But with
this fix the PTE removal path would now call vmem_altmap_free() just
because altmap is non-NULL, and would not free the actual backing page,
IIUC :)
Maybe free_vmemmap_pages() should first check that the backing page is
really inside the altmap range before using vmem_altmap_free()?
Hopefully I didn't miss anything :)
Thanks,
Lance
>Note that we'll try to get rid of that bootmem info handling soon. For
>now, we'll handle it similar to free_pagetable(), just avoiding the
>ifdef.
>
>Fixes: bf9e4e30f353 ("x86/mm: use pagetable_free()")
>Cc: stable@vger.kernel.org
>Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
>---
>Reproduced and tested with a simple VM with a virtio-mem device,
>repeatedly adding and removing memory.
>
>Found by code inspection while working on bootmem_info removal.
>---
> arch/x86/mm/init_64.c | 43 +++++++++++++++++++++++++++----------------
> 1 file changed, 27 insertions(+), 16 deletions(-)
>
>diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
>index df2261fa4f98..8d03e44a7fb9 100644
>--- a/arch/x86/mm/init_64.c
>+++ b/arch/x86/mm/init_64.c
>@@ -1014,7 +1014,7 @@ static void __meminit free_pagetable(struct page *page, int order)
> #ifdef CONFIG_HAVE_BOOTMEM_INFO_NODE
> enum bootmem_type type = bootmem_type(page);
>
>- if (type == SECTION_INFO || type == MIX_SECTION_INFO) {
>+ if (type == MIX_SECTION_INFO) {
> while (nr_pages--)
> put_page_bootmem(page++);
> } else {
>@@ -1028,13 +1028,24 @@ static void __meminit free_pagetable(struct page *page, int order)
> }
> }
>
>-static void __meminit free_hugepage_table(struct page *page,
>+static void __meminit free_vmemmap_pages(struct page *page, unsigned int order,
> struct vmem_altmap *altmap)
> {
>- if (altmap)
>- vmem_altmap_free(altmap, PMD_SIZE / PAGE_SIZE);
>- else
>- free_pagetable(page, get_order(PMD_SIZE));
>+ if (altmap) {
>+ vmem_altmap_free(altmap, 1u << order);
>+ } else if (PageReserved(page)) {
>+ unsigned long nr_pages = 1 << order;
>+
>+ if (IS_ENABLED(CONFIG_HAVE_BOOTMEM_INFO_NODE) &&
>+ bootmem_type(page) == SECTION_INFO) {
>+ while (nr_pages--)
>+ put_page_bootmem(page++);
>+ } else {
>+ free_reserved_pages(page, nr_pages);
>+ }
>+ } else {
>+ __free_pages(page, order);
>+ }
> }
>
> static void __meminit free_pte_table(pte_t *pte_start, pmd_t *pmd)
>@@ -1093,7 +1104,7 @@ static void __meminit free_pud_table(pud_t *pud_start, p4d_t *p4d)
>
> static void __meminit
> remove_pte_table(pte_t *pte_start, unsigned long addr, unsigned long end,
>- bool direct)
>+ bool direct, struct vmem_altmap *altmap)
> {
> unsigned long next, pages = 0;
> pte_t *pte;
>@@ -1118,7 +1129,7 @@ remove_pte_table(pte_t *pte_start, unsigned long addr, unsigned long end,
> return;
>
> if (!direct)
>- free_pagetable(pte_page(*pte), 0);
>+ free_vmemmap_pages(pte_page(*pte), 0, altmap);
>
> spin_lock(&init_mm.page_table_lock);
> pte_clear(&init_mm, addr, pte);
>@@ -1153,25 +1164,25 @@ remove_pmd_table(pmd_t *pmd_start, unsigned long addr, unsigned long end,
> if (IS_ALIGNED(addr, PMD_SIZE) &&
> IS_ALIGNED(next, PMD_SIZE)) {
> if (!direct)
>- free_hugepage_table(pmd_page(*pmd),
>- altmap);
>+ free_vmemmap_pages(pmd_page(*pmd),
>+ PMD_ORDER, altmap);
>
> spin_lock(&init_mm.page_table_lock);
> pmd_clear(pmd);
> spin_unlock(&init_mm.page_table_lock);
> pages++;
> } else if (vmemmap_pmd_is_unused(addr, next)) {
>- free_hugepage_table(pmd_page(*pmd),
>- altmap);
>- spin_lock(&init_mm.page_table_lock);
>- pmd_clear(pmd);
>- spin_unlock(&init_mm.page_table_lock);
>+ free_vmemmap_pages(pmd_page(*pmd), PMD_ORDER,
>+ altmap);
>+ spin_lock(&init_mm.page_table_lock);
>+ pmd_clear(pmd);
>+ spin_unlock(&init_mm.page_table_lock);
> }
> continue;
> }
>
> pte_base = (pte_t *)pmd_page_vaddr(*pmd);
>- remove_pte_table(pte_base, addr, next, direct);
>+ remove_pte_table(pte_base, addr, next, direct, altmap);
> free_pte_table(pte_base, pmd);
> }
>
>
>---
>
>base-commit: a2ddbfd1af0f54ea84bf17f0400088815d012e8d
>
>change-id: 20260428-vmemmap-ab4b949aa727
>
>--
>
>Cheers,
>
>David
>
>
^ permalink raw reply [flat|nested] 8+ messages in thread* Re: [PATCH] x86/mm: fix freeing of PMD-sized vmemmap pages
2026-04-29 2:12 ` Lance Yang
@ 2026-04-29 2:30 ` Lance Yang
2026-04-29 5:50 ` David Hildenbrand (Arm)
1 sibling, 0 replies; 8+ messages in thread
From: Lance Yang @ 2026-04-29 2:30 UTC (permalink / raw)
To: david
Cc: dave.hansen, luto, peterz, tglx, mingo, bp, x86, hpa, rppt, jgg,
baolu.lu, akpm, linux-kernel, linux-mm, stable, Lance Yang
On Wed, Apr 29, 2026 at 10:12:24AM +0800, Lance Yang wrote:
>
>On Tue, Apr 28, 2026 at 12:29:36PM +0200, David Hildenbrand (Arm) wrote:
>>In commit bf9e4e30f353 ("x86/mm: use pagetable_free()"), we switched
>>from freeing non-boot page tables through __free_pages() to
>>pagetable_free().
>>
>>However, the function is also called to free vmemmap pages.
>>
>>Given that vmemmap pages are not page tables, already the page_ptdesc(page)
>>is wrong. But worse, pagetable_free() calls
>>
>> __free_pages(page, compound_order(page));
>>
>>As vmemmap pages are not compound pages (see vmemmap_alloc_block()) --
>>except for HVO, which doesn't apply here -- we will only free the first
>>page when freeing a PMD-sized vmemmap page, leaking the other ones.
>>
>>Fix it by properly decoupling pagetable and vmemmap freeing.
>>free_pagetable() no longer has to mess with SECTION_INFO, as only the
>>vmemmap is marked like that in register_page_bootmem_memmap().
>>
>>While at it, just wire up the altmap parameter for remove_pte_table().
>>Also, the indentation in remove_pmd_table() is messed up, let's fix that
>>while touching it.
>
>One thing I'm not sure about is passing altmap down into
>remove_pte_table().
>
>Do we actually know that a non-NULL altmap means that the vmemmap
>backing page came from that altmap?
>
>On x86 we still have in vmemmap_populate():
>
> if (end - start < PAGES_PER_SECTION * sizeof(struct page))
> err = vmemmap_populate_basepages(start, end, node, NULL);
>
>So for smaller-than-section vmemmap ranges, even if the caller has an
>altmap, the backing pages are allocated from normal memory. But with
>this fix the PTE removal path would now call vmem_altmap_free() just
>because altmap is non-NULL, and would not free the actual backing page,
>IIUC :)
>
>Maybe free_vmemmap_pages() should first check that the backing page is
>really inside the altmap range before using vmem_altmap_free()?
>
>Hopefully I didn't miss anything :)
I played a bit with the following on top of this fix (untested):
---8<---
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 8d03e44a7fb9..9a52f9424a07 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -1028,14 +1028,33 @@ static void __meminit free_pagetable(struct page *page, int order)
}
}
+static bool __meminit vmemmap_page_is_altmap(struct page *page,
+ unsigned long nr_pages, struct vmem_altmap *altmap)
+{
+ unsigned long pfn = page_to_pfn(page);
+ unsigned long start_pfn;
+ unsigned long end_pfn;
+
+ if (!altmap)
+ return false;
+
+ start_pfn = altmap->base_pfn + altmap->reserve;
+ end_pfn = altmap->base_pfn + vmem_altmap_offset(altmap);
+
+ if (pfn < start_pfn || pfn >= end_pfn)
+ return false;
+
+ return nr_pages <= end_pfn - pfn;
+}
+
static void __meminit free_vmemmap_pages(struct page *page, unsigned int order,
struct vmem_altmap *altmap)
{
- if (altmap) {
- vmem_altmap_free(altmap, 1u << order);
- } else if (PageReserved(page)) {
- unsigned long nr_pages = 1 << order;
+ unsigned long nr_pages = 1 << order;
+ if (vmemmap_page_is_altmap(page, nr_pages, altmap)) {
+ vmem_altmap_free(altmap, nr_pages);
+ } else if (PageReserved(page)) {
if (IS_ENABLED(CONFIG_HAVE_BOOTMEM_INFO_NODE) &&
bootmem_type(page) == SECTION_INFO) {
while (nr_pages--)
--
Thanks,
Lance
>Thanks,
>Lance
>
>>Note that we'll try to get rid of that bootmem info handling soon. For
>>now, we'll handle it similar to free_pagetable(), just avoiding the
>>ifdef.
>>
>>Fixes: bf9e4e30f353 ("x86/mm: use pagetable_free()")
>>Cc: stable@vger.kernel.org
>>Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
>>---
>>Reproduced and tested with a simple VM with a virtio-mem device,
>>repeatedly adding and removing memory.
>>
>>Found by code inspection while working on bootmem_info removal.
>>---
>> arch/x86/mm/init_64.c | 43 +++++++++++++++++++++++++++----------------
>> 1 file changed, 27 insertions(+), 16 deletions(-)
>>
>>diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
>>index df2261fa4f98..8d03e44a7fb9 100644
>>--- a/arch/x86/mm/init_64.c
>>+++ b/arch/x86/mm/init_64.c
>>@@ -1014,7 +1014,7 @@ static void __meminit free_pagetable(struct page *page, int order)
>> #ifdef CONFIG_HAVE_BOOTMEM_INFO_NODE
>> enum bootmem_type type = bootmem_type(page);
>>
>>- if (type == SECTION_INFO || type == MIX_SECTION_INFO) {
>>+ if (type == MIX_SECTION_INFO) {
>> while (nr_pages--)
>> put_page_bootmem(page++);
>> } else {
>>@@ -1028,13 +1028,24 @@ static void __meminit free_pagetable(struct page *page, int order)
>> }
>> }
>>
>>-static void __meminit free_hugepage_table(struct page *page,
>>+static void __meminit free_vmemmap_pages(struct page *page, unsigned int order,
>> struct vmem_altmap *altmap)
>> {
>>- if (altmap)
>>- vmem_altmap_free(altmap, PMD_SIZE / PAGE_SIZE);
>>- else
>>- free_pagetable(page, get_order(PMD_SIZE));
>>+ if (altmap) {
>>+ vmem_altmap_free(altmap, 1u << order);
>>+ } else if (PageReserved(page)) {
>>+ unsigned long nr_pages = 1 << order;
>>+
>>+ if (IS_ENABLED(CONFIG_HAVE_BOOTMEM_INFO_NODE) &&
>>+ bootmem_type(page) == SECTION_INFO) {
>>+ while (nr_pages--)
>>+ put_page_bootmem(page++);
>>+ } else {
>>+ free_reserved_pages(page, nr_pages);
>>+ }
>>+ } else {
>>+ __free_pages(page, order);
>>+ }
>> }
>>
>> static void __meminit free_pte_table(pte_t *pte_start, pmd_t *pmd)
>>@@ -1093,7 +1104,7 @@ static void __meminit free_pud_table(pud_t *pud_start, p4d_t *p4d)
>>
>> static void __meminit
>> remove_pte_table(pte_t *pte_start, unsigned long addr, unsigned long end,
>>- bool direct)
>>+ bool direct, struct vmem_altmap *altmap)
>> {
>> unsigned long next, pages = 0;
>> pte_t *pte;
>>@@ -1118,7 +1129,7 @@ remove_pte_table(pte_t *pte_start, unsigned long addr, unsigned long end,
>> return;
>>
>> if (!direct)
>>- free_pagetable(pte_page(*pte), 0);
>>+ free_vmemmap_pages(pte_page(*pte), 0, altmap);
>>
>> spin_lock(&init_mm.page_table_lock);
>> pte_clear(&init_mm, addr, pte);
>>@@ -1153,25 +1164,25 @@ remove_pmd_table(pmd_t *pmd_start, unsigned long addr, unsigned long end,
>> if (IS_ALIGNED(addr, PMD_SIZE) &&
>> IS_ALIGNED(next, PMD_SIZE)) {
>> if (!direct)
>>- free_hugepage_table(pmd_page(*pmd),
>>- altmap);
>>+ free_vmemmap_pages(pmd_page(*pmd),
>>+ PMD_ORDER, altmap);
>>
>> spin_lock(&init_mm.page_table_lock);
>> pmd_clear(pmd);
>> spin_unlock(&init_mm.page_table_lock);
>> pages++;
>> } else if (vmemmap_pmd_is_unused(addr, next)) {
>>- free_hugepage_table(pmd_page(*pmd),
>>- altmap);
>>- spin_lock(&init_mm.page_table_lock);
>>- pmd_clear(pmd);
>>- spin_unlock(&init_mm.page_table_lock);
>>+ free_vmemmap_pages(pmd_page(*pmd), PMD_ORDER,
>>+ altmap);
>>+ spin_lock(&init_mm.page_table_lock);
>>+ pmd_clear(pmd);
>>+ spin_unlock(&init_mm.page_table_lock);
>> }
>> continue;
>> }
>>
>> pte_base = (pte_t *)pmd_page_vaddr(*pmd);
>>- remove_pte_table(pte_base, addr, next, direct);
>>+ remove_pte_table(pte_base, addr, next, direct, altmap);
>> free_pte_table(pte_base, pmd);
>> }
>>
>>
>>---
>>
>>base-commit: a2ddbfd1af0f54ea84bf17f0400088815d012e8d
>>
>>change-id: 20260428-vmemmap-ab4b949aa727
>>
>>--
>>
>>Cheers,
>>
>>David
>>
>>
>
^ permalink raw reply related [flat|nested] 8+ messages in thread* Re: [PATCH] x86/mm: fix freeing of PMD-sized vmemmap pages
2026-04-29 2:12 ` Lance Yang
2026-04-29 2:30 ` Lance Yang
@ 2026-04-29 5:50 ` David Hildenbrand (Arm)
1 sibling, 0 replies; 8+ messages in thread
From: David Hildenbrand (Arm) @ 2026-04-29 5:50 UTC (permalink / raw)
To: Lance Yang
Cc: dave.hansen, luto, peterz, tglx, mingo, bp, x86, hpa, rppt, jgg,
baolu.lu, akpm, linux-kernel, linux-mm, stable
On 4/29/26 04:12, Lance Yang wrote:
>
> On Tue, Apr 28, 2026 at 12:29:36PM +0200, David Hildenbrand (Arm) wrote:
>> In commit bf9e4e30f353 ("x86/mm: use pagetable_free()"), we switched
>>from freeing non-boot page tables through __free_pages() to
>> pagetable_free().
>>
>> However, the function is also called to free vmemmap pages.
>>
>> Given that vmemmap pages are not page tables, already the page_ptdesc(page)
>> is wrong. But worse, pagetable_free() calls
>>
>> __free_pages(page, compound_order(page));
>>
>> As vmemmap pages are not compound pages (see vmemmap_alloc_block()) --
>> except for HVO, which doesn't apply here -- we will only free the first
>> page when freeing a PMD-sized vmemmap page, leaking the other ones.
>>
>> Fix it by properly decoupling pagetable and vmemmap freeing.
>> free_pagetable() no longer has to mess with SECTION_INFO, as only the
>> vmemmap is marked like that in register_page_bootmem_memmap().
>>
>> While at it, just wire up the altmap parameter for remove_pte_table().
>> Also, the indentation in remove_pmd_table() is messed up, let's fix that
>> while touching it.
>
> One thing I'm not sure about is passing altmap down into
> remove_pte_table().
>
> Do we actually know that a non-NULL altmap means that the vmemmap
> backing page came from that altmap?
I thought with an altmap we'd never get into the situation of allocating outside
the altmap.
But you're right that sub-section hotplug might actually trigger this.
>
> On x86 we still have in vmemmap_populate():
>
> if (end - start < PAGES_PER_SECTION * sizeof(struct page))
> err = vmemmap_populate_basepages(start, end, node, NULL);
>
> So for smaller-than-section vmemmap ranges, even if the caller has an
> altmap, the backing pages are allocated from normal memory. But with
> this fix the PTE removal path would now call vmem_altmap_free() just
> because altmap is non-NULL, and would not free the actual backing page,
> IIUC :)
>
> Maybe free_vmemmap_pages() should first check that the backing page is
> really inside the altmap range before using vmem_altmap_free()?
Probably I'll just leave it as is for now, and simply pass "NULL" for the PTE
case like we effectively did before.
Thanks!
--
Cheers,
David
^ permalink raw reply [flat|nested] 8+ messages in thread