diff mbox series

[v2] riscv: Only extend kernel reservation if mapped read-only

Message ID 02e05df076da23fc0f52c944bbf0a5cb99e95bd6.1619708542.git.geert+renesas@glider.be (mailing list archive)
State New, archived
Headers show
Series [v2] riscv: Only extend kernel reservation if mapped read-only | expand

Commit Message

Geert Uytterhoeven April 29, 2021, 3:05 p.m. UTC
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(-)

Comments

Alexandre Ghiti May 2, 2021, 2:05 p.m. UTC | #1
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
Palmer Dabbelt May 6, 2021, 6:41 a.m. UTC | #2
On Thu, 29 Apr 2021 08:05:00 PDT (-0700), geert+renesas@glider.be wrote:
> 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

Thanks, this is on for-next
diff mbox series

Patch

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