drm/panthor: Don't add write fences to the shared BOs

[drm/drm-misc.git] / arch / arm64 / mm / contpte.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);

void contpte_clear_young_dirty_ptes(struct vm_area_struct *vma,
                                    unsigned long addr, pte_t *ptep,
                                    unsigned int nr, cydp_t flags)
{
        /*
         * We can safely clear access/dirty without needing to unfold from
         * the architectures perspective, even when contpte is set. If the
         * range starts or ends midway through a contpte block, we can just
         * expand to include the full contpte block. While this is not
         * exactly what the core-mm asked for, it tracks access/dirty per
         * folio, not per page. And since we only create a contpte block
         * when it is covered by a single folio, we can get away with
         * clearing access/dirty for the whole block.
         */
        unsigned long start = addr;
        unsigned long end = start + nr * PAGE_SIZE;

        if (pte_cont(__ptep_get(ptep + nr - 1)))
                end = ALIGN(end, CONT_PTE_SIZE);

        if (pte_cont(__ptep_get(ptep))) {
                start = ALIGN_DOWN(start, CONT_PTE_SIZE);
                ptep = contpte_align_down(ptep);
        }

        __clear_young_dirty_ptes(vma, start, ptep, (end - start) / PAGE_SIZE, flags);
}
EXPORT_SYMBOL_GPL(contpte_clear_young_dirty_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);

                /*
                 * We are not advancing entry because __ptep_set_access_flags()
                 * only consumes access flags from entry. And since we have checked
                 * for the whole contpte block and returned early, pte_same()
                 * within __ptep_set_access_flags() is likely false.
                 */
                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);