Re: [PATCH v2 0/2] arm64: Cut rebuild time when changing CONFIG_BLK_DEV_INITRD

[Mike Rapoport]

On Thu, Oct 25, 2018 at 08:15:15AM -0500, Rob Herring wrote:
> +Ard
> 
> On Thu, Oct 25, 2018 at 4:38 AM Mike Rapoport <rppt@xxxxxxxxxxxxx> wrote:
> >
> > On Wed, Oct 24, 2018 at 02:55:17PM -0500, Rob Herring wrote:
> > > On Wed, Oct 24, 2018 at 2:33 PM Florian Fainelli <f.fainelli@xxxxxxxxx> wrote:
> > > >
> > > > Hi all,
> > > >
> > > > While investigating why ARM64 required a ton of objects to be rebuilt
> > > > when toggling CONFIG_DEV_BLK_INITRD, it became clear that this was
> > > > because we define __early_init_dt_declare_initrd() differently and we do
> > > > that in arch/arm64/include/asm/memory.h which gets included by a fair
> > > > amount of other header files, and translation units as well.
> > >
> > > I scratch my head sometimes as to why some config options rebuild so
> > > much stuff. One down, ? to go. :)
> > >
> > > > Changing the value of CONFIG_DEV_BLK_INITRD is a common thing with build
> > > > systems that generate two kernels: one with the initramfs and one
> > > > without. buildroot is one of these build systems, OpenWrt is also
> > > > another one that does this.
> > > >
> > > > This patch series proposes adding an empty initrd.h to satisfy the need
> > > > for drivers/of/fdt.c to unconditionally include that file, and moves the
> > > > custom __early_init_dt_declare_initrd() definition away from
> > > > asm/memory.h
> > > >
> > > > This cuts the number of objects rebuilds from 1920 down to 26, so a
> > > > factor 73 approximately.
> > > >
> > > > Apologies for the long CC list, please let me know how you would go
> > > > about merging that and if another approach would be preferable, e.g:
> > > > introducing a CONFIG_ARCH_INITRD_BELOW_START_OK Kconfig option or
> > > > something like that.
> > >
> > > There may be a better way as of 4.20 because bootmem is now gone and
> > > only memblock is used. This should unify what each arch needs to do
> > > with initrd early. We need the physical address early for memblock
> > > reserving. Then later on we need the virtual address to access the
> > > initrd. Perhaps we should just change initrd_start and initrd_end to
> > > physical addresses (or add 2 new variables would be less invasive and
> > > allow for different translation than __va()). The sanity checks and
> > > memblock reserve could also perhaps be moved to a common location.
> > >
> > > Alternatively, given arm64 is the only oddball, I'd be fine with an
> > > "if (IS_ENABLED(CONFIG_ARM64))" condition in the default
> > > __early_init_dt_declare_initrd as long as we have a path to removing
> > > it like the above option.
> >
> > I think arm64 does not have to redefine __early_init_dt_declare_initrd().
> > Something like this might be just all we need (completely untested,
> > probably it won't even compile):
> >
> > diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> > index 9d9582c..e9ca238 100644
> > --- a/arch/arm64/mm/init.c
> > +++ b/arch/arm64/mm/init.c
> > @@ -62,6 +62,9 @@ s64 memstart_addr __ro_after_init = -1;
> >  phys_addr_t arm64_dma_phys_limit __ro_after_init;
> >
> >  #ifdef CONFIG_BLK_DEV_INITRD
> > +
> > +static phys_addr_t initrd_start_phys, initrd_end_phys;
> > +
> >  static int __init early_initrd(char *p)
> >  {
> >         unsigned long start, size;
> > @@ -71,8 +74,8 @@ static int __init early_initrd(char *p)
> >         if (*endp == ',') {
> >                 size = memparse(endp + 1, NULL);
> >
> > -               initrd_start = start;
> > -               initrd_end = start + size;
> > +               initrd_start_phys = start;
> > +               initrd_end_phys = end;
> >         }
> >         return 0;
> >  }
> > @@ -407,14 +410,27 @@ void __init arm64_memblock_init(void)
> >                 memblock_add(__pa_symbol(_text), (u64)(_end - _text));
> >         }
> >
> > -       if (IS_ENABLED(CONFIG_BLK_DEV_INITRD) && initrd_start) {
> > +       if (IS_ENABLED(CONFIG_BLK_DEV_INITRD) &&
> > +           (initrd_start || initrd_start_phys)) {
> > +               /*
> > +                * FIXME: ensure proper precendence between
> > +                * early_initrd and DT when both are present
> 
> Command line takes precedence, so just reverse the order.
> 
> > +                */
> > +               if (initrd_start) {
> > +                       initrd_start_phys = __phys_to_virt(initrd_start);
> > +                       initrd_end_phys = __phys_to_virt(initrd_end);
> 
> AIUI, the original issue was doing the P2V translation was happening
> too early and the VA could be wrong if the linear range is adjusted.
> So I don't think this would work.

Probably things have changed since then, but in the current code there is

		initrd_start = __phys_to_virt(initrd_start);

and in between only the code related to CONFIG_RANDOMIZE_BASE, so I believe
it's safe to use __phys_to_virt() here as well.
 
> I suppose you could convert the VA back to a PA before any adjustments
> and then back to a VA again after. But that's kind of hacky. 2 wrongs
> making a right.
> 
> > +               } else if (initrd_start_phys) {
> > +                       initrd_start = __va(initrd_start_phys);
> > +                       initrd_end = __va(initrd_start_phys);
> > +               }
> > +
> >                 /*
> >                  * Add back the memory we just removed if it results in the
> >                  * initrd to become inaccessible via the linear mapping.
> >                  * Otherwise, this is a no-op
> >                  */
> > -               u64 base = initrd_start & PAGE_MASK;
> > -               u64 size = PAGE_ALIGN(initrd_end) - base;
> > +               u64 base = initrd_start_phys & PAGE_MASK;
> > +               u64 size = PAGE_ALIGN(initrd_end_phys) - base;
> >
> >                 /*
> >                  * We can only add back the initrd memory if we don't end up
> > @@ -458,7 +474,7 @@ void __init arm64_memblock_init(void)
> >          * pagetables with memblock.
> >          */
> >         memblock_reserve(__pa_symbol(_text), _end - _text);
> > -#ifdef CONFIG_BLK_DEV_INITRD
> > +#if 0
> >         if (initrd_start) {
> >                 memblock_reserve(initrd_start, initrd_end - initrd_start);
> >
> >
> > > Rob
> > >
> >
> > --
> > Sincerely yours,
> > Mike.
> >
> 

-- 
Sincerely yours,
Mike.