Re: [RFC PATCH 1/3] riscv: Remove 2MB offset in the mm layout

[Guo Ren]

On Tue, Nov 23, 2021 at 9:37 PM Alexandre Ghiti
<alexandre.ghiti@xxxxxxxxxxxxx> wrote:
>
> On Tue, Nov 23, 2021 at 4:56 AM Anup Patel <anup@xxxxxxxxxxxxxx> wrote:
> >
> > +Alex
> >
> > On Tue, Nov 23, 2021 at 7:27 AM <guoren@xxxxxxxxxx> wrote:
> > >
> > > From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> > >
> > > The current RISC-V's mm layout is based on a 2MB offset and wasting
> > > memory. Remove 2MB offset and map PAGE_OFFSET at start_of_DRAM.
> > > Then we could reduce the memory reserved for opensbi in the next
> > > patch.
> >
> > The real problem is that the generic kernel marks memory before
> > __pa(PAGE_OFFSET) as reserved which is evident from the boot
> > print "OF: fdt: Ignoring memory range 0x80000000 - 0x80200000".
>
> Agreed, memblock 'rejects' this region because MIN_MEMBLOCK_ADDR is
> defined as __pa(PAGE_OFFSET) which points to 0x80200000. I have a
> patch to enable the use of hugepages for the linear mapping [1] that
> does just that, things are not that easy since then it breaks initrd
> initialization which is an early caller of __va, I updated this
> patchset a few months ago, I can push that soon @Guo Ren.
Seems your patch makes the mapping of early_pg_dir & swapper_pg_dir different.

early_pg_dir: 0x80200000 -> 0xffffffe000000000
swapper_pg_dir: 0x80000000 -> 0xffffffe000000000

It breaks the vmlinux.ld.S, doesn't it?

>
> [1] https://lkml.org/lkml/2020/6/3/696
>
>
>
> >
> > One simple way to re-claim the first 2MB of memory is by:
> > 1) Not placing OpenSBI firmware at start of RAM and rather
> > place it towards end/middle or RAM away from kernel and initrd
> > 2) Load kernel at start of the RAM
> >
> > The point#1 is already supported by OpenSBI firmwares using
> > position independent compilation. In fact, U-Boot SPL does
> > not load OpenSBI firmware at the start of RAM.
> >
> > I would suggest Allwinner D1 to follow U-Boot SPL and have
> > the booting stage before OpenSBI to load OpenSBI firmware
> > somewhere else.
> >
> > Regards,
> > Anup
> >
> > >
> > > Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> > > Cc: Palmer Dabbelt <palmer@xxxxxxxxxxx>
> > > Cc: Anup Patel <anup.patel@xxxxxxx>
> > > Cc: Atish Patra <atishp@xxxxxxxxxxxx>
> > > ---
> > >  arch/riscv/include/asm/page.h   |  8 ++++++++
> > >  arch/riscv/kernel/head.S        | 10 +++-------
> > >  arch/riscv/kernel/vmlinux.lds.S |  5 ++---
> > >  arch/riscv/mm/init.c            | 11 ++++++++---
> > >  4 files changed, 21 insertions(+), 13 deletions(-)
> > >
> > > diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
> > > index b3e5ff0125fe..299147c78b4a 100644
> > > --- a/arch/riscv/include/asm/page.h
> > > +++ b/arch/riscv/include/asm/page.h
> > > @@ -16,6 +16,14 @@
> > >  #define PAGE_SIZE      (_AC(1, UL) << PAGE_SHIFT)
> > >  #define PAGE_MASK      (~(PAGE_SIZE - 1))
> > >
> > > +#if __riscv_xlen == 64
> > > +/* Image load offset(2MB) from start of RAM */
> > > +#define LOAD_OFFSET    0x200000
> > > +#else
> > > +/* Image load offset(4MB) from start of RAM */
> > > +#define LOAD_OFFSET    0x400000
> > > +#endif
> > > +
> > >  #ifdef CONFIG_64BIT
> > >  #define HUGE_MAX_HSTATE                2
> > >  #else
> > > diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
> > > index f52f01ecbeea..a6ac892d2ccf 100644
> > > --- a/arch/riscv/kernel/head.S
> > > +++ b/arch/riscv/kernel/head.S
> > > @@ -61,13 +61,7 @@ ENTRY(_start)
> > >         /* Image load offset (0MB) from start of RAM for M-mode */
> > >         .dword 0
> > >  #else
> > > -#if __riscv_xlen == 64
> > > -       /* Image load offset(2MB) from start of RAM */
> > > -       .dword 0x200000
> > > -#else
> > > -       /* Image load offset(4MB) from start of RAM */
> > > -       .dword 0x400000
> > > -#endif
> > > +       .dword LOAD_OFFSET
> > >  #endif
> > >         /* Effective size of kernel image */
> > >         .dword _end - _start
> > > @@ -94,6 +88,8 @@ relocate:
> > >         la a1, kernel_map
> > >         XIP_FIXUP_OFFSET a1
> > >         REG_L a1, KERNEL_MAP_VIRT_ADDR(a1)
> > > +       li a2, LOAD_OFFSET
> > > +       add a1, a1, a2
> > >         la a2, _start
> > >         sub a1, a1, a2
> > >         add ra, ra, a1
> > > diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
> > > index 5104f3a871e3..75b7c72cd4bd 100644
> > > --- a/arch/riscv/kernel/vmlinux.lds.S
> > > +++ b/arch/riscv/kernel/vmlinux.lds.S
> > > @@ -11,10 +11,9 @@
> > >  #else
> > >
> > >  #include <asm/pgtable.h>
> > > -#define LOAD_OFFSET KERNEL_LINK_ADDR
> > >
> > > -#include <asm/vmlinux.lds.h>
> > >  #include <asm/page.h>
> > > +#include <asm/vmlinux.lds.h>
> > >  #include <asm/cache.h>
> > >  #include <asm/thread_info.h>
> > >  #include <asm/set_memory.h>
> > > @@ -32,7 +31,7 @@ PECOFF_FILE_ALIGNMENT = 0x200;
> > >  SECTIONS
> > >  {
> > >         /* Beginning of code and text segment */
> > > -       . = LOAD_OFFSET;
> > > +       . = LOAD_OFFSET + KERNEL_LINK_ADDR;
> > >         _start = .;
> > >         HEAD_TEXT_SECTION
> > >         . = ALIGN(PAGE_SIZE);
> > > diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> > > index 24b2b8044602..920e78f8c3e4 100644
> > > --- a/arch/riscv/mm/init.c
> > > +++ b/arch/riscv/mm/init.c
> > > @@ -221,6 +221,11 @@ static void __init setup_bootmem(void)
> > >         if (!IS_ENABLED(CONFIG_BUILTIN_DTB))
> > >                 memblock_reserve(dtb_early_pa, fdt_totalsize(dtb_early_va));
> > >
> > > +       /*
> > > +        * Reserve OpenSBI region and depends on PMP to deny accesses.
> > > +        */
> > > +       memblock_reserve(__pa(PAGE_OFFSET), LOAD_OFFSET);
> > > +
> > >         early_init_fdt_scan_reserved_mem();
> > >         dma_contiguous_reserve(dma32_phys_limit);
> > >         if (IS_ENABLED(CONFIG_64BIT))
> > > @@ -604,7 +609,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
> > >
> > >         kernel_map.va_kernel_xip_pa_offset = kernel_map.virt_addr - kernel_map.xiprom;
> > >  #else
> > > -       kernel_map.phys_addr = (uintptr_t)(&_start);
> > > +       kernel_map.phys_addr = (uintptr_t)(&_start) - LOAD_OFFSET;
> > >         kernel_map.size = (uintptr_t)(&_end) - kernel_map.phys_addr;
> > >  #endif
> > >         kernel_map.va_pa_offset = PAGE_OFFSET - kernel_map.phys_addr;
> > > @@ -645,8 +650,8 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
> > >         create_pmd_mapping(trampoline_pmd, kernel_map.virt_addr,
> > >                            kernel_map.xiprom, PMD_SIZE, PAGE_KERNEL_EXEC);
> > >  #else
> > > -       create_pmd_mapping(trampoline_pmd, kernel_map.virt_addr,
> > > -                          kernel_map.phys_addr, PMD_SIZE, PAGE_KERNEL_EXEC);
> > > +       create_pmd_mapping(trampoline_pmd, kernel_map.virt_addr + LOAD_OFFSET,
> > > +                          kernel_map.phys_addr + LOAD_OFFSET, PMD_SIZE, PAGE_KERNEL_EXEC);
> > >  #endif
> > >  #else
> > >         /* Setup trampoline PGD */
> > > --
> > > 2.25.1
> > >



-- 
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/