Re: [PATCH v2] memblock: make memblock_find_in_range method private

[Mike Rapoport <rppt@kernel.org>]

Hi Rob,

On Mon, Aug 02, 2021 at 08:55:57AM -0600, Rob Herring wrote:
> On Mon, Aug 2, 2021 at 12:37 AM Mike Rapoport <rppt@kernel.org> wrote:
> >
> > From: Mike Rapoport <rppt@linux.ibm.com>
> >
> > There are a lot of uses of memblock_find_in_range() along with
> > memblock_reserve() from the times memblock allocation APIs did not exist.
> >
> > memblock_find_in_range() is the very core of memblock allocations, so any
> > future changes to its internal behaviour would mandate updates of all the
> > users outside memblock.
> >
> > Replace the calls to memblock_find_in_range() with an equivalent calls to
> > memblock_phys_alloc() and memblock_phys_alloc_range() and make
> > memblock_find_in_range() private method of memblock.
> >
> > This simplifies the callers, ensures that (unlikely) errors in
> > memblock_reserve() are handled and improves maintainability of
> > memblock_find_in_range().
> >
> > Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> > ---
> > v2: don't change error message in arm::reserve_crashkernel(), per Russell
> > v1: https://lore.kernel.org/lkml/20210730104039.7047-1-rppt@kernel.org
> >
> >  arch/arm/kernel/setup.c           | 18 +++++--------
> >  arch/arm64/kvm/hyp/reserved_mem.c |  9 +++----
> >  arch/arm64/mm/init.c              | 36 ++++++++-----------------
> >  arch/mips/kernel/setup.c          | 14 +++++-----
> >  arch/riscv/mm/init.c              | 44 ++++++++++---------------------
> >  arch/s390/kernel/setup.c          | 10 ++++---
> >  arch/x86/kernel/aperture_64.c     |  5 ++--
> >  arch/x86/mm/init.c                | 21 +++++++++------
> >  arch/x86/mm/numa.c                |  5 ++--
> >  arch/x86/mm/numa_emulation.c      |  5 ++--
> >  arch/x86/realmode/init.c          |  2 +-
> >  drivers/acpi/tables.c             |  5 ++--
> >  drivers/base/arch_numa.c          |  5 +---
> >  drivers/of/of_reserved_mem.c      | 12 ++++++---
> >  include/linux/memblock.h          |  2 --
> >  mm/memblock.c                     |  2 +-
> >  16 files changed, 78 insertions(+), 117 deletions(-)
> >
> > diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
> > index f97eb2371672..67f5421b2af7 100644
> > --- a/arch/arm/kernel/setup.c
> > +++ b/arch/arm/kernel/setup.c
> > @@ -1012,31 +1012,25 @@ static void __init reserve_crashkernel(void)
> >                 unsigned long long lowmem_max = __pa(high_memory - 1) + 1;
> >                 if (crash_max > lowmem_max)
> >                         crash_max = lowmem_max;
> > -               crash_base = memblock_find_in_range(CRASH_ALIGN, crash_max,
> > -                                                   crash_size, CRASH_ALIGN);
> > +
> > +               crash_base = memblock_phys_alloc_range(crash_size, CRASH_ALIGN,
> > +                                                      CRASH_ALIGN, crash_max);
> >                 if (!crash_base) {
> >                         pr_err("crashkernel reservation failed - No suitable area found.\n");
> >                         return;
> >                 }
> >         } else {
> > +               unsigned long long crash_max = crash_base + crash_size;
> >                 unsigned long long start;
> >
> > -               start = memblock_find_in_range(crash_base,
> > -                                              crash_base + crash_size,
> > -                                              crash_size, SECTION_SIZE);
> > +               start = memblock_phys_alloc_range(crash_size, SECTION_SIZE,
> > +                                                 crash_base, crash_max);
> >                 if (start != crash_base) {
> 
> If this is true and start is non-zero, then you need an
> memblock_free(). However, since the range is equal to the size, then
> that can never happen and just checking !start is sufficient.

Agree. Will update.
 
> >                         pr_err("crashkernel reservation failed - memory is in use.\n");
> >                         return;
> >                 }
> >         }
> >
> > -       ret = memblock_reserve(crash_base, crash_size);
> > -       if (ret < 0) {
> > -               pr_warn("crashkernel reservation failed - memory is in use (0x%lx)\n",
> > -                       (unsigned long)crash_base);
> > -               return;
> > -       }
> > -
> >         pr_info("Reserving %ldMB of memory at %ldMB for crashkernel (System RAM: %ldMB)\n",
> >                 (unsigned long)(crash_size >> 20),
> >                 (unsigned long)(crash_base >> 20),
> > diff --git a/arch/arm64/kvm/hyp/reserved_mem.c b/arch/arm64/kvm/hyp/reserved_mem.c
> > index d654921dd09b..578670e3f608 100644
> > --- a/arch/arm64/kvm/hyp/reserved_mem.c
> > +++ b/arch/arm64/kvm/hyp/reserved_mem.c
> > @@ -92,12 +92,10 @@ void __init kvm_hyp_reserve(void)
> >          * this is unmapped from the host stage-2, and fallback to PAGE_SIZE.
> >          */
> >         hyp_mem_size = hyp_mem_pages << PAGE_SHIFT;
> > -       hyp_mem_base = memblock_find_in_range(0, memblock_end_of_DRAM(),
> > -                                             ALIGN(hyp_mem_size, PMD_SIZE),
> > -                                             PMD_SIZE);
> > +       hyp_mem_base = memblock_phys_alloc(ALIGN(hyp_mem_size, PMD_SIZE),
> > +                                          PMD_SIZE);
> >         if (!hyp_mem_base)
> > -               hyp_mem_base = memblock_find_in_range(0, memblock_end_of_DRAM(),
> > -                                                     hyp_mem_size, PAGE_SIZE);
> > +               hyp_mem_base = memblock_phys_alloc(hyp_mem_size, PAGE_SIZE);
> >         else
> >                 hyp_mem_size = ALIGN(hyp_mem_size, PMD_SIZE);
> >
> > @@ -105,7 +103,6 @@ void __init kvm_hyp_reserve(void)
> >                 kvm_err("Failed to reserve hyp memory\n");
> >                 return;
> >         }
> > -       memblock_reserve(hyp_mem_base, hyp_mem_size);
> >
> >         kvm_info("Reserved %lld MiB at 0x%llx\n", hyp_mem_size >> 20,
> >                  hyp_mem_base);
> > diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> > index 8490ed2917ff..d566478a06dd 100644
> > --- a/arch/arm64/mm/init.c
> > +++ b/arch/arm64/mm/init.c
> > @@ -74,6 +74,7 @@ phys_addr_t arm64_dma_phys_limit __ro_after_init;
> >  static void __init reserve_crashkernel(void)
> >  {
> >         unsigned long long crash_base, crash_size;
> > +       unsigned long crash_max = arm64_dma_phys_limit;
> 
> It all works out to the same size, but it doesn't make sense that
> crash_base and crash_size are long long and crash_max is long.

Indeed, thanks.
 
> >         int ret;
> >
> >         ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(),
> > @@ -84,33 +85,18 @@ static void __init reserve_crashkernel(void)
> >
> >         crash_size = PAGE_ALIGN(crash_size);
> >
> > -       if (crash_base == 0) {
> > -               /* Current arm64 boot protocol requires 2MB alignment */
> > -               crash_base = memblock_find_in_range(0, arm64_dma_phys_limit,
> > -                               crash_size, SZ_2M);
> > -               if (crash_base == 0) {
> > -                       pr_warn("cannot allocate crashkernel (size:0x%llx)\n",
> > -                               crash_size);
> > -                       return;
> > -               }
> > -       } else {
> > -               /* User specifies base address explicitly. */
> > -               if (!memblock_is_region_memory(crash_base, crash_size)) {
> > -                       pr_warn("cannot reserve crashkernel: region is not memory\n");
> > -                       return;
> > -               }
> > +       /* User specifies base address explicitly. */
> > +       if (crash_base)
> > +               crash_max = crash_base + crash_size;
> >
> > -               if (memblock_is_region_reserved(crash_base, crash_size)) {
> > -                       pr_warn("cannot reserve crashkernel: region overlaps reserved memory\n");
> > -                       return;
> > -               }
> > -
> > -               if (!IS_ALIGNED(crash_base, SZ_2M)) {
> > -                       pr_warn("cannot reserve crashkernel: base address is not 2MB aligned\n");
> > -                       return;
> 
> We've lost the alignment check.
> 
> Perhaps memblock_phys_alloc_range() should check that the start
> matches the alignment. That would simplify the return handling as it
> seems NULL is not the only error case.

We only lost pr_warn() about the alignment check. When crash_base != 0, we
are trying to allocate the exact [base, base + size) region aligned at 2M.
If it is free we get the address, if not we get 0.
 
> > -               }
> > +       /* Current arm64 boot protocol requires 2MB alignment */
> > +       crash_base = memblock_phys_alloc_range(crash_size, SZ_2M,
> > +                                              crash_base, crash_max);
> > +       if (!crash_base) {
> > +               pr_warn("cannot allocate crashkernel (size:0x%llx)\n",
> > +                       crash_size);
> > +               return;
> >         }
> > -       memblock_reserve(crash_base, crash_size);
> >
> >         pr_info("crashkernel reserved: 0x%016llx - 0x%016llx (%lld MB)\n",
> >                 crash_base, crash_base + crash_size, crash_size >> 20);
> 
> [...]
> 
> > diff --git a/arch/x86/realmode/init.c b/arch/x86/realmode/init.c
> > index 6534c92d0f83..31b5856010cb 100644
> > --- a/arch/x86/realmode/init.c
> > +++ b/arch/x86/realmode/init.c
> > @@ -28,7 +28,7 @@ void __init reserve_real_mode(void)
> >         WARN_ON(slab_is_available());
> >
> >         /* Has to be under 1M so we can execute real-mode AP code. */
> > -       mem = memblock_find_in_range(0, 1<<20, size, PAGE_SIZE);
> > +       mem = memblock_phys_alloc_range(size, PAGE_SIZE, 0, 1<<20);
> >         if (!mem)
> >                 pr_info("No sub-1M memory is available for the trampoline\n");
> >         else
> 
> Don't you need to drop the memblock_reserve() after this?

Nope, it reserves the entire first 1M, which is more than we allocated
here. The call to memblock_reserve() in memblock_phys_alloc_range() will be
redundant here, but IMHO it's clearer this way.

-- 
Sincerely yours,
Mike.