linux-kernel - Re: [PATCH] fixup: mm/rmap: extend rmap and migration support device-private entries

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Message-Id: <20251114165146.5c51eeeee200bd37b378bd45@linux-foundation.org>
Date: Fri, 14 Nov 2025 16:51:46 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Balbir Singh <balbirs@...dia.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 dri-devel@...ts.freedesktop.org, David Hildenbrand <david@...hat.com>, Zi
 Yan <ziy@...dia.com>, Joshua Hahn <joshua.hahnjy@...il.com>, Rakie Kim
 <rakie.kim@...com>, Byungchul Park <byungchul@...com>, Gregory Price
 <gourry@...rry.net>, Ying Huang <ying.huang@...ux.alibaba.com>, Alistair
 Popple <apopple@...dia.com>, Oscar Salvador <osalvador@...e.de>, Lorenzo
 Stoakes <lorenzo.stoakes@...cle.com>, Baolin Wang
 <baolin.wang@...ux.alibaba.com>, "Liam R. Howlett"
 <Liam.Howlett@...cle.com>, Nico Pache <npache@...hat.com>, Ryan Roberts
 <ryan.roberts@....com>, Dev Jain <dev.jain@....com>, Barry Song
 <baohua@...nel.org>, Lyude Paul <lyude@...hat.com>, Danilo Krummrich
 <dakr@...nel.org>, David Airlie <airlied@...il.com>, Simona Vetter
 <simona@...ll.ch>, Ralph Campbell <rcampbell@...dia.com>, Mika
 Penttilä <mpenttil@...hat.com>, Matthew Brost
 <matthew.brost@...el.com>, Francois Dugast <francois.dugast@...el.com>
Subject: Re: [PATCH] fixup: mm/rmap: extend rmap and migration support
 device-private entries

On Sat, 15 Nov 2025 11:28:35 +1100 Balbir Singh <balbirs@...dia.com> wrote:

> Follow the pattern used in remove_migration_pte() in
> remove_migration_pmd(). Process the migration entries and if the entry
> type is device private, override the pmde with a device private entry
> and set the soft dirty and uffd_wp bits with the pmd_swp_mksoft_dirty
> and pmd_swp_mkuffd_wp
> 
> ...
>
> This fixup should be squashed into the patch "mm/rmap: extend rmap and
> migration support" of mm/mm-unstable
> 

OK.  After fixing up
mm-replace-pmd_to_swp_entry-with-softleaf_from_pmd.patch, mm.git's
mm/huge_memory.c has the below.  Please double-check.

void remove_migration_pmd(struct page_vma_mapped_walk *pvmw, struct page *new)
{
	struct folio *folio = page_folio(new);
	struct vm_area_struct *vma = pvmw->vma;
	struct mm_struct *mm = vma->vm_mm;
	unsigned long address = pvmw->address;
	unsigned long haddr = address & HPAGE_PMD_MASK;
	pmd_t pmde;
	softleaf_t entry;

	if (!(pvmw->pmd && !pvmw->pte))
		return;

	entry = softleaf_from_pmd(*pvmw->pmd);
	folio_get(folio);
	pmde = folio_mk_pmd(folio, READ_ONCE(vma->vm_page_prot));

	if (pmd_swp_soft_dirty(*pvmw->pmd))
		pmde = pmd_mksoft_dirty(pmde);
	if (softleaf_is_migration_write(entry))
		pmde = pmd_mkwrite(pmde, vma);
	if (pmd_swp_uffd_wp(*pvmw->pmd))
		pmde = pmd_mkuffd_wp(pmde);
	if (!softleaf_is_migration_young(entry))
		pmde = pmd_mkold(pmde);
	/* NOTE: this may contain setting soft-dirty on some archs */
	if (folio_test_dirty(folio) && softleaf_is_migration_dirty(entry))
		pmde = pmd_mkdirty(pmde);

	if (folio_is_device_private(folio)) {
		swp_entry_t entry;

		if (pmd_write(pmde))
			entry = make_writable_device_private_entry(
							page_to_pfn(new));
		else
			entry = make_readable_device_private_entry(
							page_to_pfn(new));
		pmde = swp_entry_to_pmd(entry);

		if (pmd_swp_soft_dirty(*pvmw->pmd))
			pmde = pmd_swp_mksoft_dirty(pmde);
		if (pmd_swp_uffd_wp(*pvmw->pmd))
			pmde = pmd_swp_mkuffd_wp(pmde);
	}

	if (folio_test_anon(folio)) {
		rmap_t rmap_flags = RMAP_NONE;

		if (!softleaf_is_migration_read(entry))
			rmap_flags |= RMAP_EXCLUSIVE;

		folio_add_anon_rmap_pmd(folio, new, vma, haddr, rmap_flags);
	} else {
		folio_add_file_rmap_pmd(folio, new, vma);
	}
	VM_BUG_ON(pmd_write(pmde) && folio_test_anon(folio) && !PageAnonExclusive(new));
	set_pmd_at(mm, haddr, pvmw->pmd, pmde);

	/* No need to invalidate - it was non-present before */
	update_mmu_cache_pmd(vma, address, pvmw->pmd);
	trace_remove_migration_pmd(address, pmd_val(pmde));
}