Messages in this thread |  | | Subject | Re: [PATCH v2] riscv: Only extend kernel reservation if mapped read-only | From | Alex Ghiti <> | Date | Sun, 2 May 2021 10:05:05 -0400 |
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Le 4/29/21 à 11:05 AM, Geert Uytterhoeven a écrit : > When the kernel mapping was moved outside of the linear mapping, the > kernel memory reservation was increased, to take into account mapping > granularity. However, this is done unconditionally, regardless of > whether the kernel memory is mapped read-only or not. > > If this extension is not needed, up to 2 MiB may be lost, which has a > big impact on e.g. Canaan K210 (64-bit nommu) platforms with only 8 MiB > of RAM. > > Reclaim the lost memory by only extending the reserved region when > needed, i.e. depending on a simplified version of the conditional logic > around the call to protect_kernel_linear_mapping_text_rodata(). > > Fixes: 2bfc6cd81bd17e43 ("riscv: Move kernel mapping outside of linear mapping") > Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be> > --- > v2: > - Simplify the conditional, as STRICT_KERNEL_RWX depends on > MMU && !XIP_KERNEL. > > Only tested on K210 (SiPeed MAIX BiT): > > -Memory: 5852K/8192K available (1344K kernel code, 147K rwdata, 272K rodata, 106K init, 72K bss, 2340K reserved, 0K cma-reserved) > +Memory: 5948K/8192K available (1344K kernel code, 147K rwdata, 272K rodata, 106K init, 72K bss, 2244K reserved, 0K cma-reserved) > > Yes, I was lucky, as only 96 KiB was lost ;-) > --- > arch/riscv/mm/init.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c > index 788eb222deacf994..3ebc0f5d2b73b42b 100644 > --- a/arch/riscv/mm/init.c > +++ b/arch/riscv/mm/init.c > @@ -136,11 +136,16 @@ void __init setup_bootmem(void) > > /* > * Reserve from the start of the kernel to the end of the kernel > - * and make sure we align the reservation on PMD_SIZE since we will > + */ > +#if defined(CONFIG_64BIT) && defined(CONFIG_STRICT_KERNEL_RWX) > + /* > + * Make sure we align the reservation on PMD_SIZE since we will > * map the kernel in the linear mapping as read-only: we do not want > * any allocation to happen between _end and the next pmd aligned page. > */ > - memblock_reserve(vmlinux_start, (vmlinux_end - vmlinux_start + PMD_SIZE - 1) & PMD_MASK); > + vmlinux_end = (vmlinux_end + PMD_SIZE - 1) & PMD_MASK; > +#endif > + memblock_reserve(vmlinux_start, vmlinux_end - vmlinux_start); > > /* > * memblock allocator is not aware of the fact that last 4K bytes of >
I tested this on the following configs:
- rv32_defconfig (build and valid on qemu) - defconfig (with and without CONFIG_STRICT_KERNEL_RWX) (build and valid on qemu) - xip kernel (build and valid on qemu) - nommu_k210_defconfig (build only)
so you can add:
Tested-by: Alexandre Ghiti <alex@ghiti.fr>
Thank you again for that,
Alex
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