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

Mark Rutland
2019-05-03T10:05:18Z

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.

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

Thanks,
Mark.