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highmem: introduce clear_user_highpages()

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Define clear_user_highpages() which uses the range clearing primitive,
clear_user_pages().  We can safely use this when CONFIG_HIGHMEM is
disabled and if the architecture does not have clear_user_highpage.

The first is needed to ensure that contiguous page ranges stay contiguous
which precludes intermediate maps via HIGMEM.  The second, because if the
architecture has clear_user_highpage(), it likely needs flushing magic
when clearing the page, magic that we aren't privy to.

For both of those cases, just fallback to a loop around
clear_user_highpage().

Link: https://lkml.kernel.org/r/20260107072009.1615991-4-ankur.a.arora@oracle.com
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: "Borislav Petkov (AMD)" <bp@alien8.de>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Konrad Rzessutek Wilk <konrad.wilk@oracle.com>
Cc: Lance Yang <ioworker0@gmail.com>
Cc: "Liam R. Howlett" <Liam.Howlett@oracle.com>
Cc: Li Zhe <lizhe.67@bytedance.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Raghavendra K T <raghavendra.kt@amd.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Ankur Arora
2026-01-06 23:20:04 -08:00
committed by Andrew Morton
parent 62a9f5a85b
commit 8d846b723e
1 changed files with 44 additions and 1 deletions
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45
include/linux/highmem.h
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@@ -251,7 +251,14 @@ static inline void clear_user_pages(void *addr, unsigned long vaddr,
#endif
}
/* when CONFIG_HIGHMEM is not set these will be plain clear/copy_page */
/**
* clear_user_highpage() - clear a page to be mapped to user space
* @page: start page
* @vaddr: start address of the user mapping
*
* With !CONFIG_HIGHMEM this (and the copy_user_highpage() below) will
* be plain clear_user_page() (and copy_user_page()).
*/
static inline void clear_user_highpage(struct page *page, unsigned long vaddr)
{
void *addr = kmap_local_page(page);
@@ -260,6 +267,42 @@ static inline void clear_user_highpage(struct page *page, unsigned long vaddr)
}
#endif /* clear_user_highpage */
/**
* clear_user_highpages() - clear a page range to be mapped to user space
* @page: start page
* @vaddr: start address of the user mapping
* @npages: number of pages
*
* Assumes that all the pages in the region (@page, +@npages) are valid
* so this does no exception handling.
*/
static inline void clear_user_highpages(struct page *page, unsigned long vaddr,
unsigned int npages)
{
#if defined(clear_user_highpage) || defined(CONFIG_HIGHMEM)
/*
* An architecture defined clear_user_highpage() implies special
* handling is needed.
*
* So we use that or, the generic variant if CONFIG_HIGHMEM is
* enabled.
*/
do {
clear_user_highpage(page, vaddr);
vaddr += PAGE_SIZE;
page++;
} while (--npages);
#else
/*
* Prefer clear_user_pages() to allow for architectural optimizations
* when operating on contiguous page ranges.
*/
clear_user_pages(page_address(page), vaddr, page, npages);
#endif
}
#ifndef vma_alloc_zeroed_movable_folio
/**
* vma_alloc_zeroed_movable_folio - Allocate a zeroed page for a VMA.