linux/arch/arm64/mm/contpte.c
Ryan Roberts 94c18d5f7e arm64/mm: improve comment in contpte_ptep_get_lockless()
Make clear the atmicity/consistency requirements of the API and how we
achieve them.

Link: https://lore.kernel.org/linux-mm/Zc-Tqqfksho3BHmU@arm.com/
Link: https://lkml.kernel.org/r/20240226120321.1055731-3-ryan.roberts@arm.com
Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2024-03-04 17:01:18 -08:00

409 lines
12 KiB
C

// SPDX-License-Identifier: GPL-2.0-only
/*
* Copyright (C) 2023 ARM Ltd.
*/
#include <linux/mm.h>
#include <linux/efi.h>
#include <linux/export.h>
#include <asm/tlbflush.h>
static inline bool mm_is_user(struct mm_struct *mm)
{
/*
* Don't attempt to apply the contig bit to kernel mappings, because
* dynamically adding/removing the contig bit can cause page faults.
* These racing faults are ok for user space, since they get serialized
* on the PTL. But kernel mappings can't tolerate faults.
*/
if (unlikely(mm_is_efi(mm)))
return false;
return mm != &init_mm;
}
static inline pte_t *contpte_align_down(pte_t *ptep)
{
return PTR_ALIGN_DOWN(ptep, sizeof(*ptep) * CONT_PTES);
}
static void contpte_try_unfold_partial(struct mm_struct *mm, unsigned long addr,
pte_t *ptep, unsigned int nr)
{
/*
* Unfold any partially covered contpte block at the beginning and end
* of the range.
*/
if (ptep != contpte_align_down(ptep) || nr < CONT_PTES)
contpte_try_unfold(mm, addr, ptep, __ptep_get(ptep));
if (ptep + nr != contpte_align_down(ptep + nr)) {
unsigned long last_addr = addr + PAGE_SIZE * (nr - 1);
pte_t *last_ptep = ptep + nr - 1;
contpte_try_unfold(mm, last_addr, last_ptep,
__ptep_get(last_ptep));
}
}
static void contpte_convert(struct mm_struct *mm, unsigned long addr,
pte_t *ptep, pte_t pte)
{
struct vm_area_struct vma = TLB_FLUSH_VMA(mm, 0);
unsigned long start_addr;
pte_t *start_ptep;
int i;
start_ptep = ptep = contpte_align_down(ptep);
start_addr = addr = ALIGN_DOWN(addr, CONT_PTE_SIZE);
pte = pfn_pte(ALIGN_DOWN(pte_pfn(pte), CONT_PTES), pte_pgprot(pte));
for (i = 0; i < CONT_PTES; i++, ptep++, addr += PAGE_SIZE) {
pte_t ptent = __ptep_get_and_clear(mm, addr, ptep);
if (pte_dirty(ptent))
pte = pte_mkdirty(pte);
if (pte_young(ptent))
pte = pte_mkyoung(pte);
}
__flush_tlb_range(&vma, start_addr, addr, PAGE_SIZE, true, 3);
__set_ptes(mm, start_addr, start_ptep, pte, CONT_PTES);
}
void __contpte_try_fold(struct mm_struct *mm, unsigned long addr,
pte_t *ptep, pte_t pte)
{
/*
* We have already checked that the virtual and pysical addresses are
* correctly aligned for a contpte mapping in contpte_try_fold() so the
* remaining checks are to ensure that the contpte range is fully
* covered by a single folio, and ensure that all the ptes are valid
* with contiguous PFNs and matching prots. We ignore the state of the
* access and dirty bits for the purpose of deciding if its a contiguous
* range; the folding process will generate a single contpte entry which
* has a single access and dirty bit. Those 2 bits are the logical OR of
* their respective bits in the constituent pte entries. In order to
* ensure the contpte range is covered by a single folio, we must
* recover the folio from the pfn, but special mappings don't have a
* folio backing them. Fortunately contpte_try_fold() already checked
* that the pte is not special - we never try to fold special mappings.
* Note we can't use vm_normal_page() for this since we don't have the
* vma.
*/
unsigned long folio_start, folio_end;
unsigned long cont_start, cont_end;
pte_t expected_pte, subpte;
struct folio *folio;
struct page *page;
unsigned long pfn;
pte_t *orig_ptep;
pgprot_t prot;
int i;
if (!mm_is_user(mm))
return;
page = pte_page(pte);
folio = page_folio(page);
folio_start = addr - (page - &folio->page) * PAGE_SIZE;
folio_end = folio_start + folio_nr_pages(folio) * PAGE_SIZE;
cont_start = ALIGN_DOWN(addr, CONT_PTE_SIZE);
cont_end = cont_start + CONT_PTE_SIZE;
if (folio_start > cont_start || folio_end < cont_end)
return;
pfn = ALIGN_DOWN(pte_pfn(pte), CONT_PTES);
prot = pte_pgprot(pte_mkold(pte_mkclean(pte)));
expected_pte = pfn_pte(pfn, prot);
orig_ptep = ptep;
ptep = contpte_align_down(ptep);
for (i = 0; i < CONT_PTES; i++) {
subpte = pte_mkold(pte_mkclean(__ptep_get(ptep)));
if (!pte_same(subpte, expected_pte))
return;
expected_pte = pte_advance_pfn(expected_pte, 1);
ptep++;
}
pte = pte_mkcont(pte);
contpte_convert(mm, addr, orig_ptep, pte);
}
EXPORT_SYMBOL_GPL(__contpte_try_fold);
void __contpte_try_unfold(struct mm_struct *mm, unsigned long addr,
pte_t *ptep, pte_t pte)
{
/*
* We have already checked that the ptes are contiguous in
* contpte_try_unfold(), so just check that the mm is user space.
*/
if (!mm_is_user(mm))
return;
pte = pte_mknoncont(pte);
contpte_convert(mm, addr, ptep, pte);
}
EXPORT_SYMBOL_GPL(__contpte_try_unfold);
pte_t contpte_ptep_get(pte_t *ptep, pte_t orig_pte)
{
/*
* Gather access/dirty bits, which may be populated in any of the ptes
* of the contig range. We are guaranteed to be holding the PTL, so any
* contiguous range cannot be unfolded or otherwise modified under our
* feet.
*/
pte_t pte;
int i;
ptep = contpte_align_down(ptep);
for (i = 0; i < CONT_PTES; i++, ptep++) {
pte = __ptep_get(ptep);
if (pte_dirty(pte))
orig_pte = pte_mkdirty(orig_pte);
if (pte_young(pte))
orig_pte = pte_mkyoung(orig_pte);
}
return orig_pte;
}
EXPORT_SYMBOL_GPL(contpte_ptep_get);
pte_t contpte_ptep_get_lockless(pte_t *orig_ptep)
{
/*
* The ptep_get_lockless() API requires us to read and return *orig_ptep
* so that it is self-consistent, without the PTL held, so we may be
* racing with other threads modifying the pte. Usually a READ_ONCE()
* would suffice, but for the contpte case, we also need to gather the
* access and dirty bits from across all ptes in the contiguous block,
* and we can't read all of those neighbouring ptes atomically, so any
* contiguous range may be unfolded/modified/refolded under our feet.
* Therefore we ensure we read a _consistent_ contpte range by checking
* that all ptes in the range are valid and have CONT_PTE set, that all
* pfns are contiguous and that all pgprots are the same (ignoring
* access/dirty). If we find a pte that is not consistent, then we must
* be racing with an update so start again. If the target pte does not
* have CONT_PTE set then that is considered consistent on its own
* because it is not part of a contpte range.
*/
pgprot_t orig_prot;
unsigned long pfn;
pte_t orig_pte;
pgprot_t prot;
pte_t *ptep;
pte_t pte;
int i;
retry:
orig_pte = __ptep_get(orig_ptep);
if (!pte_valid_cont(orig_pte))
return orig_pte;
orig_prot = pte_pgprot(pte_mkold(pte_mkclean(orig_pte)));
ptep = contpte_align_down(orig_ptep);
pfn = pte_pfn(orig_pte) - (orig_ptep - ptep);
for (i = 0; i < CONT_PTES; i++, ptep++, pfn++) {
pte = __ptep_get(ptep);
prot = pte_pgprot(pte_mkold(pte_mkclean(pte)));
if (!pte_valid_cont(pte) ||
pte_pfn(pte) != pfn ||
pgprot_val(prot) != pgprot_val(orig_prot))
goto retry;
if (pte_dirty(pte))
orig_pte = pte_mkdirty(orig_pte);
if (pte_young(pte))
orig_pte = pte_mkyoung(orig_pte);
}
return orig_pte;
}
EXPORT_SYMBOL_GPL(contpte_ptep_get_lockless);
void contpte_set_ptes(struct mm_struct *mm, unsigned long addr,
pte_t *ptep, pte_t pte, unsigned int nr)
{
unsigned long next;
unsigned long end;
unsigned long pfn;
pgprot_t prot;
/*
* The set_ptes() spec guarantees that when nr > 1, the initial state of
* all ptes is not-present. Therefore we never need to unfold or
* otherwise invalidate a range before we set the new ptes.
* contpte_set_ptes() should never be called for nr < 2.
*/
VM_WARN_ON(nr == 1);
if (!mm_is_user(mm))
return __set_ptes(mm, addr, ptep, pte, nr);
end = addr + (nr << PAGE_SHIFT);
pfn = pte_pfn(pte);
prot = pte_pgprot(pte);
do {
next = pte_cont_addr_end(addr, end);
nr = (next - addr) >> PAGE_SHIFT;
pte = pfn_pte(pfn, prot);
if (((addr | next | (pfn << PAGE_SHIFT)) & ~CONT_PTE_MASK) == 0)
pte = pte_mkcont(pte);
else
pte = pte_mknoncont(pte);
__set_ptes(mm, addr, ptep, pte, nr);
addr = next;
ptep += nr;
pfn += nr;
} while (addr != end);
}
EXPORT_SYMBOL_GPL(contpte_set_ptes);
void contpte_clear_full_ptes(struct mm_struct *mm, unsigned long addr,
pte_t *ptep, unsigned int nr, int full)
{
contpte_try_unfold_partial(mm, addr, ptep, nr);
__clear_full_ptes(mm, addr, ptep, nr, full);
}
EXPORT_SYMBOL_GPL(contpte_clear_full_ptes);
pte_t contpte_get_and_clear_full_ptes(struct mm_struct *mm,
unsigned long addr, pte_t *ptep,
unsigned int nr, int full)
{
contpte_try_unfold_partial(mm, addr, ptep, nr);
return __get_and_clear_full_ptes(mm, addr, ptep, nr, full);
}
EXPORT_SYMBOL_GPL(contpte_get_and_clear_full_ptes);
int contpte_ptep_test_and_clear_young(struct vm_area_struct *vma,
unsigned long addr, pte_t *ptep)
{
/*
* ptep_clear_flush_young() technically requires us to clear the access
* flag for a _single_ pte. However, the core-mm code actually tracks
* access/dirty per folio, not per page. And since we only create a
* contig range when the range is covered by a single folio, we can get
* away with clearing young for the whole contig range here, so we avoid
* having to unfold.
*/
int young = 0;
int i;
ptep = contpte_align_down(ptep);
addr = ALIGN_DOWN(addr, CONT_PTE_SIZE);
for (i = 0; i < CONT_PTES; i++, ptep++, addr += PAGE_SIZE)
young |= __ptep_test_and_clear_young(vma, addr, ptep);
return young;
}
EXPORT_SYMBOL_GPL(contpte_ptep_test_and_clear_young);
int contpte_ptep_clear_flush_young(struct vm_area_struct *vma,
unsigned long addr, pte_t *ptep)
{
int young;
young = contpte_ptep_test_and_clear_young(vma, addr, ptep);
if (young) {
/*
* See comment in __ptep_clear_flush_young(); same rationale for
* eliding the trailing DSB applies here.
*/
addr = ALIGN_DOWN(addr, CONT_PTE_SIZE);
__flush_tlb_range_nosync(vma, addr, addr + CONT_PTE_SIZE,
PAGE_SIZE, true, 3);
}
return young;
}
EXPORT_SYMBOL_GPL(contpte_ptep_clear_flush_young);
void contpte_wrprotect_ptes(struct mm_struct *mm, unsigned long addr,
pte_t *ptep, unsigned int nr)
{
/*
* If wrprotecting an entire contig range, we can avoid unfolding. Just
* set wrprotect and wait for the later mmu_gather flush to invalidate
* the tlb. Until the flush, the page may or may not be wrprotected.
* After the flush, it is guaranteed wrprotected. If it's a partial
* range though, we must unfold, because we can't have a case where
* CONT_PTE is set but wrprotect applies to a subset of the PTEs; this
* would cause it to continue to be unpredictable after the flush.
*/
contpte_try_unfold_partial(mm, addr, ptep, nr);
__wrprotect_ptes(mm, addr, ptep, nr);
}
EXPORT_SYMBOL_GPL(contpte_wrprotect_ptes);
int contpte_ptep_set_access_flags(struct vm_area_struct *vma,
unsigned long addr, pte_t *ptep,
pte_t entry, int dirty)
{
unsigned long start_addr;
pte_t orig_pte;
int i;
/*
* Gather the access/dirty bits for the contiguous range. If nothing has
* changed, its a noop.
*/
orig_pte = pte_mknoncont(ptep_get(ptep));
if (pte_val(orig_pte) == pte_val(entry))
return 0;
/*
* We can fix up access/dirty bits without having to unfold the contig
* range. But if the write bit is changing, we must unfold.
*/
if (pte_write(orig_pte) == pte_write(entry)) {
/*
* For HW access management, we technically only need to update
* the flag on a single pte in the range. But for SW access
* management, we need to update all the ptes to prevent extra
* faults. Avoid per-page tlb flush in __ptep_set_access_flags()
* and instead flush the whole range at the end.
*/
ptep = contpte_align_down(ptep);
start_addr = addr = ALIGN_DOWN(addr, CONT_PTE_SIZE);
for (i = 0; i < CONT_PTES; i++, ptep++, addr += PAGE_SIZE)
__ptep_set_access_flags(vma, addr, ptep, entry, 0);
if (dirty)
__flush_tlb_range(vma, start_addr, addr,
PAGE_SIZE, true, 3);
} else {
__contpte_try_unfold(vma->vm_mm, addr, ptep, orig_pte);
__ptep_set_access_flags(vma, addr, ptep, entry, dirty);
}
return 1;
}
EXPORT_SYMBOL_GPL(contpte_ptep_set_access_flags);