Re: [PATCH v5 2/2] riscv: turn pgtable_l4|[l5]_enabled to static key for RV64

[Jisheng Zhang <jszhang@kernel.org>]

On Fri, Jul 15, 2022 at 05:04:38PM +0200, Emil Renner Berthing wrote:
> On Fri, 15 Jul 2022 at 15:59, Jisheng Zhang <jszhang@kernel.org> wrote:
> > On a specific HW platform, pgtable_l4|[l5]_enabled won't change after
> > boot, and the check sits at hot code path, this characteristic makes it
> > suitable for optimization with static key.
> >
> > _pgtable_l4|[l5]_enabled is used very early during boot, even is used
> > with MMU off, so the static key mechanism isn't ready. For this case,
> > we use another static key _pgtable_lx_ready to indicate whether we
> > have finalised pgtable_l4|[l5]_enabled or not, then fall back to
> > _pgtable_l4|[l5]_enabled_early bool.
> >
> > Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
> > Reviewed-by: Anup Patel <anup@brainfault.org>
> > ---
> >  arch/riscv/include/asm/pgalloc.h    | 16 ++++----
> >  arch/riscv/include/asm/pgtable-32.h |  3 ++
> >  arch/riscv/include/asm/pgtable-64.h | 60 ++++++++++++++++++---------
> >  arch/riscv/include/asm/pgtable.h    |  5 +--
> >  arch/riscv/kernel/cpu.c             |  4 +-
> >  arch/riscv/mm/init.c                | 64 ++++++++++++++++++-----------
> >  arch/riscv/mm/kasan_init.c          | 16 ++++----
> >  7 files changed, 103 insertions(+), 65 deletions(-)
> >
> > diff --git a/arch/riscv/include/asm/pgalloc.h b/arch/riscv/include/asm/pgalloc.h
> > index 947f23d7b6af..0280eeb4756f 100644
> > --- a/arch/riscv/include/asm/pgalloc.h
> > +++ b/arch/riscv/include/asm/pgalloc.h
> > @@ -41,7 +41,7 @@ static inline void pud_populate(struct mm_struct *mm, pud_t *pud, pmd_t *pmd)
> >
> >  static inline void p4d_populate(struct mm_struct *mm, p4d_t *p4d, pud_t *pud)
> >  {
> > -       if (pgtable_l4_enabled) {
> > +       if (pgtable_l4_enabled()) {
> >                 unsigned long pfn = virt_to_pfn(pud);
> >
> >                 set_p4d(p4d, __p4d((pfn << _PAGE_PFN_SHIFT) | _PAGE_TABLE));
> > @@ -51,7 +51,7 @@ static inline void p4d_populate(struct mm_struct *mm, p4d_t *p4d, pud_t *pud)
> >  static inline void p4d_populate_safe(struct mm_struct *mm, p4d_t *p4d,
> >                                      pud_t *pud)
> >  {
> > -       if (pgtable_l4_enabled) {
> > +       if (pgtable_l4_enabled()) {
> >                 unsigned long pfn = virt_to_pfn(pud);
> >
> >                 set_p4d_safe(p4d,
> > @@ -61,7 +61,7 @@ static inline void p4d_populate_safe(struct mm_struct *mm, p4d_t *p4d,
> >
> >  static inline void pgd_populate(struct mm_struct *mm, pgd_t *pgd, p4d_t *p4d)
> >  {
> > -       if (pgtable_l5_enabled) {
> > +       if (pgtable_l5_enabled()) {
> >                 unsigned long pfn = virt_to_pfn(p4d);
> >
> >                 set_pgd(pgd, __pgd((pfn << _PAGE_PFN_SHIFT) | _PAGE_TABLE));
> > @@ -71,7 +71,7 @@ static inline void pgd_populate(struct mm_struct *mm, pgd_t *pgd, p4d_t *p4d)
> >  static inline void pgd_populate_safe(struct mm_struct *mm, pgd_t *pgd,
> >                                      p4d_t *p4d)
> >  {
> > -       if (pgtable_l5_enabled) {
> > +       if (pgtable_l5_enabled()) {
> >                 unsigned long pfn = virt_to_pfn(p4d);
> >
> >                 set_pgd_safe(pgd,
> > @@ -82,7 +82,7 @@ static inline void pgd_populate_safe(struct mm_struct *mm, pgd_t *pgd,
> >  #define pud_alloc_one pud_alloc_one
> >  static inline pud_t *pud_alloc_one(struct mm_struct *mm, unsigned long addr)
> >  {
> > -       if (pgtable_l4_enabled)
> > +       if (pgtable_l4_enabled())
> >                 return __pud_alloc_one(mm, addr);
> >
> >         return NULL;
> > @@ -91,7 +91,7 @@ static inline pud_t *pud_alloc_one(struct mm_struct *mm, unsigned long addr)
> >  #define pud_free pud_free
> >  static inline void pud_free(struct mm_struct *mm, pud_t *pud)
> >  {
> > -       if (pgtable_l4_enabled)
> > +       if (pgtable_l4_enabled())
> >                 __pud_free(mm, pud);
> >  }
> >
> > @@ -100,7 +100,7 @@ static inline void pud_free(struct mm_struct *mm, pud_t *pud)
> >  #define p4d_alloc_one p4d_alloc_one
> >  static inline p4d_t *p4d_alloc_one(struct mm_struct *mm, unsigned long addr)
> >  {
> > -       if (pgtable_l5_enabled) {
> > +       if (pgtable_l5_enabled()) {
> >                 gfp_t gfp = GFP_PGTABLE_USER;
> >
> >                 if (mm == &init_mm)
> > @@ -120,7 +120,7 @@ static inline void __p4d_free(struct mm_struct *mm, p4d_t *p4d)
> >  #define p4d_free p4d_free
> >  static inline void p4d_free(struct mm_struct *mm, p4d_t *p4d)
> >  {
> > -       if (pgtable_l5_enabled)
> > +       if (pgtable_l5_enabled())
> >                 __p4d_free(mm, p4d);
> >  }
> >
> > diff --git a/arch/riscv/include/asm/pgtable-32.h b/arch/riscv/include/asm/pgtable-32.h
> > index 59ba1fbaf784..1ef52079179a 100644
> > --- a/arch/riscv/include/asm/pgtable-32.h
> > +++ b/arch/riscv/include/asm/pgtable-32.h
> > @@ -17,6 +17,9 @@
> >
> >  #define MAX_POSSIBLE_PHYSMEM_BITS 34
> >
> > +#define pgtable_l5_enabled() 0
> > +#define pgtable_l4_enabled() 0
> > +
> >  /*
> >   * rv32 PTE format:
> >   * | XLEN-1  10 | 9             8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0
> > diff --git a/arch/riscv/include/asm/pgtable-64.h b/arch/riscv/include/asm/pgtable-64.h
> > index 5c2aba5efbd0..edfff00d8ca3 100644
> > --- a/arch/riscv/include/asm/pgtable-64.h
> > +++ b/arch/riscv/include/asm/pgtable-64.h
> > @@ -8,18 +8,38 @@
> >
> >  #include <linux/bits.h>
> >  #include <linux/const.h>
> > +#include <linux/jump_label.h>
> >  #include <asm/errata_list.h>
> >
> > -extern bool pgtable_l4_enabled;
> > -extern bool pgtable_l5_enabled;
> > +extern bool _pgtable_l5_enabled_early;
> > +extern bool _pgtable_l4_enabled_early;
> > +extern struct static_key_false _pgtable_l5_enabled;
> > +extern struct static_key_false _pgtable_l4_enabled;
> > +extern struct static_key_false _pgtable_lx_ready;
> 
> It amounts to the same, but I wonder if we ought to use the
> DECLARE_STATIC_KEY_FALSE macro here.

Thanks for the hint, will send out a newer version soon. Before
that, I will wait a bit for other review feedbacks.

Thanks