riscv: mm: skip pgtable level check in {pud,p4d}_alloc_one

riscv: mm: skip pgtable level check in {pud,p4d}_alloc_one

Patch series "move pagetable_*_dtor() to __tlb_remove_table()", v5.

As proposed [1] by Peter Zijlstra below, this patch series aims to move
pagetable_*_dtor() into __tlb_remove_table().  This will cleanup
pagetable_*_dtor() a bit and more gracefully fix the UAF issue [2]
reported by syzbot.

: Notably:
:
:  - s390 pud isn't calling the existing pagetable_pud_[cd]tor()
:  - none of the p4d things have pagetable_p4d_[cd]tor() (x86,arm64,s390,riscv)
:    and they have inconsistent accounting
:  - while much of the _ctor calls are in generic code, many of the _dtor
:    calls are in arch code for hysterial raisins, this could easily be
:    fixed
:  - if we fix ptlock_free() to handle NULL, then all the _dtor()
:    functions can use it, and we can observe they're all identical
:    and can be folded
:
: after all that cleanup, you can move the _dtor from *_free_tlb() into
: tlb_remove_table() -- which for the above case, would then have it called
: from __tlb_remove_table_free().

This patch (of 16):

{pmd,pud,p4d}_alloc_one() is never called if the corresponding page table
level is folded, as {pmd,pud,p4d}_alloc() already does the required check.
We can therefore remove the runtime page table level checks in
{pud,p4d}_alloc_one.  The PUD helper becomes equivalent to the generic
version, so we remove it altogether.

This is consistent with the way arm64 and x86 handle this situation
(runtime check in p4d_free() only).

Link: https://lkml.kernel.org/r/cover.1736317725.git.zhengqi.arch@bytedance.com
Link: https://lkml.kernel.org/r/93a1c6bddc0ded9f1a9f15658c1e4af5c93d1194.1736317725.git.zhengqi.arch@bytedance.com
Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Alexandre Ghiti <alex@ghiti.fr>
Cc: Andreas Larsson <andreas@gaisler.com>
Cc: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Cc: Will Deacon <will@kernel.org>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>