Re: [PATCH v2 09/28] ARM: mmu: Specify size in bytes in create_sections()

[Sascha Hauer <s.hauer@pengutronix.de>]

On Thu, May 17, 2018 at 12:01:34AM -0700, Andrey Smirnov wrote:
> On Wed, May 16, 2018 at 11:55 PM, Sascha Hauer <s.hauer@pengutronix.de> wrote:
> > On Wed, May 16, 2018 at 01:00:17PM -0700, Andrey Smirnov wrote:
> >> Seeing
> >>
> >>         create_sections(ttb, 0, PAGE_SIZE, ...);
> >>
> >> as the code the creates initial flat 4 GiB mapping is a bit less
> >> intuitive then
> >>
> >>         create_sections(ttb, 0, SZ_4G, ...);
> >>
> >> so, for the sake of clarification, convert create_sections() to accept
> >> size in bytes and do bytes -> MiB converstion as a part of the
> >> function.
> >>
> >> NOTE: To keep all of the arguments of create_sections() 32-bit:
> >>
> >>     - Move all of the real code into a helper function accepting first
> >>       and last addresses of the region (e.g passing 0 and U32_MAX
> >>       means all 4GiB of address space)
> >>
> >>     - Convert create_section() into a macro that does necessary size
> >>       -> last addres conversion under the hood to preserve original API
> >>
> >> Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
> >> ---
> >>  arch/arm/cpu/mmu-early.c |  4 ++--
> >>  arch/arm/cpu/mmu.c       |  4 ++--
> >>  arch/arm/cpu/mmu.h       | 22 ++++++++++++++++------
> >>  3 files changed, 20 insertions(+), 10 deletions(-)
> >>
> >> diff --git a/arch/arm/cpu/mmu-early.c b/arch/arm/cpu/mmu-early.c
> >> index 70ece0d2f..136b33c3a 100644
> >> --- a/arch/arm/cpu/mmu-early.c
> >> +++ b/arch/arm/cpu/mmu-early.c
> >> @@ -16,7 +16,7 @@ static void map_cachable(unsigned long start, unsigned long size)
> >>       start = ALIGN_DOWN(start, SZ_1M);
> >>       size  = ALIGN(size, SZ_1M);
> >>
> >> -     create_sections(ttb, start, size >> 20, PMD_SECT_AP_WRITE |
> >> +     create_sections(ttb, start, size, PMD_SECT_AP_WRITE |
> >>                       PMD_SECT_AP_READ | PMD_TYPE_SECT | PMD_SECT_WB);
> >>  }
> >>
> >> @@ -30,7 +30,7 @@ void mmu_early_enable(unsigned long membase, unsigned long memsize,
> >>       set_ttbr(ttb);
> >>       set_domain(DOMAIN_MANAGER);
> >>
> >> -     create_sections(ttb, 0, 4096, PMD_SECT_AP_WRITE |
> >> +     create_sections(ttb, 0, SZ_4G, PMD_SECT_AP_WRITE |
> >>                       PMD_SECT_AP_READ | PMD_TYPE_SECT);
> >>
> >>       map_cachable(membase, memsize);
> >> diff --git a/arch/arm/cpu/mmu.c b/arch/arm/cpu/mmu.c
> >> index 0c367e47c..f02c99f65 100644
> >> --- a/arch/arm/cpu/mmu.c
> >> +++ b/arch/arm/cpu/mmu.c
> >> @@ -460,7 +460,7 @@ static int mmu_init(void)
> >>       set_domain(DOMAIN_MANAGER);
> >>
> >>       /* create a flat mapping using 1MiB sections */
> >> -     create_sections(ttb, 0, PAGE_SIZE, PMD_SECT_AP_WRITE | PMD_SECT_AP_READ |
> >> +     create_sections(ttb, 0, SZ_4G, PMD_SECT_AP_WRITE | PMD_SECT_AP_READ |
> >>                       PMD_TYPE_SECT);
> >>       __mmu_cache_flush();
> >>
> >> @@ -472,7 +472,7 @@ static int mmu_init(void)
> >>        * below
> >>        */
> >>       for_each_memory_bank(bank) {
> >> -             create_sections(ttb, bank->start, bank->size >> 20,
> >> +             create_sections(ttb, bank->start, bank->size,
> >>                               PMD_SECT_DEF_CACHED);
> >>               __mmu_cache_flush();
> >>       }
> >> diff --git a/arch/arm/cpu/mmu.h b/arch/arm/cpu/mmu.h
> >> index d71cd7e38..52689359a 100644
> >> --- a/arch/arm/cpu/mmu.h
> >> +++ b/arch/arm/cpu/mmu.h
> >> @@ -27,16 +27,26 @@ static inline void set_domain(unsigned val)
> >>  }
> >>
> >>  static inline void
> >> -create_sections(uint32_t *ttb, unsigned long addr,
> >> -             int size_m, unsigned int flags)
> >> +__create_sections(uint32_t *ttb, unsigned long first,
> >> +               unsigned long last, unsigned int flags)
> >>  {
> >> -     unsigned long ttb_start = addr >> 20;
> >> -     unsigned long ttb_end   = ttb_start + size_m;
> >> -     unsigned int i;
> >> +     unsigned long ttb_start = first >> 20;
> >> +     unsigned long ttb_end   = (last >> 20) + 1;
> >> +     unsigned int i, addr;
> >>
> >> -     for (i = ttb_start; i < ttb_end; i++, addr += SZ_1M)
> >> +     for (i = ttb_start, addr = first; i < ttb_end; i++, addr += SZ_1M)
> >>               ttb[i] = addr | flags;
> >>  }
> >>
> >> +#define create_sections(ttb, addr, size, flags)                              \
> >> +     ({                                                              \
> >> +             typeof(addr) __addr = addr;                             \
> >> +             typeof(size) __size = size;                             \
> >> +             /* Check for overflow */                                \
> >> +             BUG_ON(__addr > ULONG_MAX - __size + 1);                \
> >> +             __create_sections(ttb, __addr, __addr + (size)  - 1,    \
> >> +                               flags);                               \
> >> +     })
> >
> > Why do you preserve the original API of create_sections()? I would just
> > change it. We have only a few callers and they are easy to change.
> >
> 
> Mostly because it keeps "addr + size - 1" arithmetic in one place
> instead of spreading it to every caller. If you'd rather have that
> instead of the macro above, I can change that in v3.

I agree that the end address calculation often is a source for
off-by-one errors, still I would prefer not using macros to hide that.

Sascha


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