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Merge patch series "riscv: Increase mmap_rnd_bits_max on Sv48/57"

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Sami Tolvanen <samitolvanen@google.com> says:

We noticed that 64-bit RISC-V kernels limit mmap_rnd_bits to 24
even if the hardware supports a larger virtual address space size
[1]. These two patches allow mmap_rnd_bits_max to be changed during
init, and bumps up the maximum randomness if we end up setting up
4/5-level paging at boot.

* b4-shazam-merge:
  riscv: mm: Update mmap_rnd_bits_max
  mm: Change mmap_rnd_bits_max to __ro_after_init

Link: https://lore.kernel.org/r/20230929211155.3910949-4-samitolvanen@google.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
This commit is contained in:
Palmer Dabbelt 2024-01-24 07:07:45 -08:00
commit d7e76ce7b7
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3 changed files with 8 additions and 2 deletions
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6
arch/riscv/mm/init.c
View File

@ -767,6 +767,11 @@ static int __init print_no5lvl(char *p)
}
early_param("no5lvl", print_no5lvl);
static void __init set_mmap_rnd_bits_max(void)
{
mmap_rnd_bits_max = MMAP_VA_BITS - PAGE_SHIFT - 3;
}
/*
* There is a simple way to determine if 4-level is supported by the
* underlying hardware: establish 1:1 mapping in 4-level page table mode
@ -1081,6 +1086,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
#if defined(CONFIG_64BIT) && !defined(CONFIG_XIP_KERNEL)
set_satp_mode(dtb_pa);
set_mmap_rnd_bits_max();
#endif
/*

2
include/linux/mm.h
View File

@ -86,7 +86,7 @@ extern int sysctl_legacy_va_layout;
#ifdef CONFIG_HAVE_ARCH_MMAP_RND_BITS
extern const int mmap_rnd_bits_min;
extern const int mmap_rnd_bits_max;
extern int mmap_rnd_bits_max __ro_after_init;
extern int mmap_rnd_bits __read_mostly;
#endif
#ifdef CONFIG_HAVE_ARCH_MMAP_RND_COMPAT_BITS

2
mm/mmap.c
View File

@ -64,7 +64,7 @@
#ifdef CONFIG_HAVE_ARCH_MMAP_RND_BITS
const int mmap_rnd_bits_min = CONFIG_ARCH_MMAP_RND_BITS_MIN;
const int mmap_rnd_bits_max = CONFIG_ARCH_MMAP_RND_BITS_MAX;
int mmap_rnd_bits_max __ro_after_init = CONFIG_ARCH_MMAP_RND_BITS_MAX;
int mmap_rnd_bits __read_mostly = CONFIG_ARCH_MMAP_RND_BITS;
#endif
#ifdef CONFIG_HAVE_ARCH_MMAP_RND_COMPAT_BITS