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    SubjectRe: [PATCH] arm64/mm: Drop redundant BUG_ON(!pgtable_alloc)
    On Fri, Nov 18, 2022 at 11:01:02AM +0530, Anshuman Khandual wrote:
    > __create_pgd_mapping_locked() expects a page allocator used while mapping a
    > virtual range. This page allocator function propagates down the call chain,
    > while building intermediate levels in the page table. Passed page allocator
    > is a necessary ingredient required to build the page table but its presence
    > can be asserted just once in the very beginning rather than in all the down
    > stream functions. This consolidates BUG_ON(!pgtable_alloc) checks just in a
    > single place i.e __create_pgd_mapping_locked().
    >
    > Cc: Catalin Marinas <catalin.marinas@arm.com>
    > Cc: Will Deacon <will@kernel.org>
    > Cc: Mark Rutland <mark.rutland@arm.com>
    > Cc: Andrew Morton <akpm@linux-foundation.org>
    > Cc: linux-arm-kernel@lists.infradead.org
    > Cc: linux-kernel@vger.kernel.org
    > Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>

    I don't have strong feelings either way, so FWIW:

    Acked-by: Mark Rutland <mark.rutland@arm.com>

    Thanks,
    Mark.

    > ---
    > This applies on v6.1-rc5
    >
    > arch/arm64/mm/mmu.c | 4 +---
    > 1 file changed, 1 insertion(+), 3 deletions(-)
    >
    > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
    > index 5a19950e7289..97ca82001089 100644
    > --- a/arch/arm64/mm/mmu.c
    > +++ b/arch/arm64/mm/mmu.c
    > @@ -207,7 +207,6 @@ static void alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr,
    >
    > if (flags & NO_EXEC_MAPPINGS)
    > pmdval |= PMD_TABLE_PXN;
    > - BUG_ON(!pgtable_alloc);
    > pte_phys = pgtable_alloc(PAGE_SHIFT);
    > __pmd_populate(pmdp, pte_phys, pmdval);
    > pmd = READ_ONCE(*pmdp);
    > @@ -285,7 +284,6 @@ static void alloc_init_cont_pmd(pud_t *pudp, unsigned long addr,
    >
    > if (flags & NO_EXEC_MAPPINGS)
    > pudval |= PUD_TABLE_PXN;
    > - BUG_ON(!pgtable_alloc);
    > pmd_phys = pgtable_alloc(PMD_SHIFT);
    > __pud_populate(pudp, pmd_phys, pudval);
    > pud = READ_ONCE(*pudp);
    > @@ -324,7 +322,6 @@ static void alloc_init_pud(pgd_t *pgdp, unsigned long addr, unsigned long end,
    >
    > if (flags & NO_EXEC_MAPPINGS)
    > p4dval |= P4D_TABLE_PXN;
    > - BUG_ON(!pgtable_alloc);
    > pud_phys = pgtable_alloc(PUD_SHIFT);
    > __p4d_populate(p4dp, pud_phys, p4dval);
    > p4d = READ_ONCE(*p4dp);
    > @@ -383,6 +380,7 @@ static void __create_pgd_mapping_locked(pgd_t *pgdir, phys_addr_t phys,
    > phys &= PAGE_MASK;
    > addr = virt & PAGE_MASK;
    > end = PAGE_ALIGN(virt + size);
    > + BUG_ON(!pgtable_alloc);
    >
    > do {
    > next = pgd_addr_end(addr, end);
    > --
    > 2.25.1
    >

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