Re: [PATCH 04/15] arm64: switch to generic version of pte allocation

Mike Rapoport
2019-05-05T06:19:57Z

On Fri, May 03, 2019 at 11:05:09AM +0100, Mark Rutland wrote:
> Hi,
>
> On Thu, May 02, 2019 at 06:28:31PM +0300, Mike Rapoport wrote:
> > The PTE allocations in arm64 are identical to the generic ones modulo the
> > GFP flags.
> >
> > Using the generic pte_alloc_one() functions ensures that the user page
> > tables are allocated with __GFP_ACCOUNT set.
> >
> > The arm64 definition of PGALLOC_GFP is removed and replaced with
> > GFP_PGTABLE_USER for p[gum]d_alloc_one() and for KVM memory cache.
> >
> > The mappings created with create_pgd_mapping() are now using
> > GFP_PGTABLE_KERNEL.
> >
> > The conversion to the generic version of pte_free_kernel() removes the NULL
> > check for pte.
> >
> > The pte_free() version on arm64 is identical to the generic one and
> > can be simply dropped.
> >
> > Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> > ---
> > arch/arm64/include/asm/pgalloc.h | 43 ++++------------------------------------
> > arch/arm64/mm/mmu.c | 2 +-
> > arch/arm64/mm/pgd.c | 4 ++--
> > virt/kvm/arm/mmu.c | 2 +-
> > 4 files changed, 8 insertions(+), 43 deletions(-)
>
> [...]
>
> > diff --git a/arch/arm64/mm/pgd.c b/arch/arm64/mm/pgd.c
> > index 289f911..2ef1a53 100644
> > --- a/arch/arm64/mm/pgd.c
> > +++ b/arch/arm64/mm/pgd.c
> > @@ -31,9 +31,9 @@ static struct kmem_cache *pgd_cache __ro_after_init;
> > pgd_t *pgd_alloc(struct mm_struct *mm)
> > {
> > if (PGD_SIZE == PAGE_SIZE)
> > - return (pgd_t *)__get_free_page(PGALLOC_GFP);
> > + return (pgd_t *)__get_free_page(GFP_PGTABLE_USER);
> > else
> > - return kmem_cache_alloc(pgd_cache, PGALLOC_GFP);
> > + return kmem_cache_alloc(pgd_cache, GFP_PGTABLE_USER);
> > }
>
> In efi_virtmap_init() we use pgd_alloc() to allocate a pgd for EFI
> runtime services, which we map with a special kernel page table.
>
> I'm not sure if accounting that is problematic, as it's allocated in a
> kernel thread off the back of an early_initcall.

The accounting bypasses kernel threads so there should be no problem.

> Just to check, Is that sound, or do we need a pgd_alloc_kernel()?
>
> Thanks,
> Mark.
>

--
Sincerely yours,
Mike.