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Date: Tue, 28 Jan 2020 11:28:34 -0800
From: Atish Patra <atishp@...shpatra.org>
To: Anup Patel <anup@...infault.org>
Cc: Atish Patra <atish.patra@....com>,
Albert Ou <aou@...s.berkeley.edu>,
Thomas Gleixner <tglx@...utronix.de>,
Kees Cook <keescook@...omium.org>,
Abner Chang <abner.chang@....com>, nickhu@...estech.com,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Palmer Dabbelt <palmerdabbelt@...gle.com>,
Heiko Carstens <heiko.carstens@...ibm.com>,
"linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
Mike Rapoport <rppt@...ux.ibm.com>,
Chester Lin <clin@...e.com>,
Vincent Chen <vincent.chen@...ive.com>,
Geert Uytterhoeven <geert@...ux-m68k.org>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
Paul Walmsley <paul.walmsley@...ive.com>,
Greentime Hu <greentime.hu@...ive.com>,
linux-riscv <linux-riscv@...ts.infradead.org>,
Borislav Petkov <bp@...e.de>,
Palmer Dabbelt <palmer@...belt.com>,
Mao Han <han_mao@...ky.com>
Subject: Re: [PATCH v7 07/10] RISC-V: Move relocate and few other functions
out of __init
On Mon, Jan 27, 2020 at 8:38 PM Anup Patel <anup@...infault.org> wrote:
>
> On Tue, Jan 28, 2020 at 7:58 AM Atish Patra <atish.patra@....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@....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
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