Re: [PATCH v7 07/10] RISC-V: Move relocate and few other functions out of __init

[Atish Patra <atishp@atishpatra.org>]

On Mon, Jan 27, 2020 at 8:38 PM Anup Patel <anup@brainfault.org> wrote:
>
> On Tue, Jan 28, 2020 at 7:58 AM Atish Patra <atish.patra@wdc.com> wrote:
> >
> > The secondary hart booting and relocation code are under .init section.
> > As a result, it will be freed once kernel booting is done. However,
> > ordered booting protocol and CPU hotplug always requires these sections
> > to be present to bringup harts after initial kernel boot.
> >
> > Move the required sections to a different section and make sure that
> > they are in memory within first 2MB offset as trampoline page directory
> > only maps first 2MB.
> >
> > Signed-off-by: Atish Patra <atish.patra@wdc.com>
> > ---
> >  arch/riscv/kernel/head.S        | 73 +++++++++++++++++++--------------
> >  arch/riscv/kernel/vmlinux.lds.S |  9 +++-
> >  2 files changed, 50 insertions(+), 32 deletions(-)
> >
> > diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
> > index a4242be66966..9d7f084a50cc 100644
> > --- a/arch/riscv/kernel/head.S
> > +++ b/arch/riscv/kernel/head.S
> > @@ -14,7 +14,7 @@
> >  #include <asm/hwcap.h>
> >  #include <asm/image.h>
> >
> > -__INIT
> > +__HEAD
> >  ENTRY(_start)
> >         /*
> >          * Image header expected by Linux boot-loaders. The image header data
> > @@ -44,9 +44,10 @@ ENTRY(_start)
> >         .balign 4
> >         .ascii RISCV_IMAGE_MAGIC2
> >         .word 0
> > +END(_start)
> >
> > -.global _start_kernel
> > -_start_kernel:
> > +       __INIT
> > +ENTRY(_start_kernel)
> >         /* Mask all interrupts */
> >         csrw CSR_IE, zero
> >         csrw CSR_IP, zero
> > @@ -125,6 +126,37 @@ clear_bss_done:
> >         call parse_dtb
> >         tail start_kernel
> >
> > +.Lsecondary_start:
> > +#ifdef CONFIG_SMP
> > +       /* Set trap vector to spin forever to help debug */
> > +       la a3, .Lsecondary_park
> > +       csrw CSR_TVEC, a3
> > +
> > +       slli a3, a0, LGREG
> > +       la a1, __cpu_up_stack_pointer
> > +       la a2, __cpu_up_task_pointer
> > +       add a1, a3, a1
> > +       add a2, a3, a2
> > +
> > +       /*
> > +        * This hart didn't win the lottery, so we wait for the winning hart to
> > +        * get far enough along the boot process that it should continue.
> > +        */
> > +.Lwait_for_cpu_up:
> > +       /* FIXME: We should WFI to save some energy here. */
> > +       REG_L sp, (a1)
> > +       REG_L tp, (a2)
> > +       beqz sp, .Lwait_for_cpu_up
> > +       beqz tp, .Lwait_for_cpu_up
> > +       fence
> > +
> > +       tail secondary_start_common
> > +#endif
> > +
> > +END(_start_kernel)
> > +
> > +.section ".noinit.text","ax",@progbits
> > +.align 2
>
> Try to use __HEAD here (if possible).
>


> >  #ifdef CONFIG_MMU
> >  relocate:
> >         /* Relocate return address */
> > @@ -177,41 +209,27 @@ relocate:
> >
> >         ret
> >  #endif /* CONFIG_MMU */
> > -
> > -.Lsecondary_start:
> >  #ifdef CONFIG_SMP
> >         /* Set trap vector to spin forever to help debug */
> >         la a3, .Lsecondary_park
> >         csrw CSR_TVEC, a3
> >
> >         slli a3, a0, LGREG
> > -       la a1, __cpu_up_stack_pointer
> > -       la a2, __cpu_up_task_pointer
> > -       add a1, a3, a1
> > -       add a2, a3, a2
> > -
> > -       /*
> > -        * This hart didn't win the lottery, so we wait for the winning hart to
> > -        * get far enough along the boot process that it should continue.
> > -        */
> > -.Lwait_for_cpu_up:
> > -       /* FIXME: We should WFI to save some energy here. */
> > -       REG_L sp, (a1)
> > -       REG_L tp, (a2)
> > -       beqz sp, .Lwait_for_cpu_up
> > -       beqz tp, .Lwait_for_cpu_up
> > -       fence
> > +       .global secondary_start_common
> > +secondary_start_common:
> >
> >  #ifdef CONFIG_MMU
> >         /* Enable virtual memory and relocate to virtual address */
> >         la a0, swapper_pg_dir
> >         call relocate
> >  #endif
> > -
> >         tail smp_callin
> > -#endif
> > +#endif /* CONFIG_SMP */
> >
> > -END(_start)
> > +.Lsecondary_park:
> > +       /* We lack SMP support or have too many harts, so park this hart */
> > +       wfi
> > +       j .Lsecondary_park
> >
> >  #ifdef CONFIG_RISCV_M_MODE
> >  ENTRY(reset_regs)
> > @@ -292,13 +310,6 @@ ENTRY(reset_regs)
> >  END(reset_regs)
> >  #endif /* CONFIG_RISCV_M_MODE */
> >
> > -.section ".text", "ax",@progbits
> > -.align 2
> > -.Lsecondary_park:
> > -       /* We lack SMP support or have too many harts, so park this hart */
> > -       wfi
> > -       j .Lsecondary_park
> > -
> >  __PAGE_ALIGNED_BSS
> >         /* Empty zero page */
> >         .balign PAGE_SIZE
> > diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
> > index 12f42f96d46e..c8a88326df9e 100644
> > --- a/arch/riscv/kernel/vmlinux.lds.S
> > +++ b/arch/riscv/kernel/vmlinux.lds.S
> > @@ -10,6 +10,7 @@
> >  #include <asm/cache.h>
> >  #include <asm/thread_info.h>
> >
> > +#include <linux/sizes.h>
> >  OUTPUT_ARCH(riscv)
> >  ENTRY(_start)
> >
> > @@ -20,8 +21,14 @@ SECTIONS
> >         /* Beginning of code and text segment */
> >         . = LOAD_OFFSET;
> >         _start = .;
> > -       __init_begin = .;
> >         HEAD_TEXT_SECTION
> > +       .noinit.text :
> > +       {
> > +               *(.noinit.text)
> > +       }
>
> Can we try using HEAD_TEXT_SECTION for SMP booting
> related functions instead of new ".noinit.text" section ??
>

Yeah. That is much cleaner as well. I will update it in v2.

> > +       . = ALIGN(SZ_4K);
>
> Change this to PAGE aligned:
>     . = ALIGN(PAGE_SIZE)
>

Sure. Will do that.

> > +
> > +       __init_begin = .;
> >         INIT_TEXT_SECTION(PAGE_SIZE)
> >         INIT_DATA_SECTION(16)
> >         /* we have to discard exit text and such at runtime, not link time */
> > --
> > 2.24.0
> >
>
> Regards,
> Anup
>


-- 
Regards,
Atish