From Documentation/admin-guide/kernel-parameters.txt:
rodata= [KNL,EARLY]
on Mark read-only kernel memory as read-only (default).
So "rodata=on" is the default.
But the current code does not follow the document, it makes "rodata=full"
as the default.
This patch refactors the "rodata=xxx" :
1.) Make rodata=on behaviour be the original rodata=full.
(Drop the original rodata=full.)
2.) Introduce "rodata=noalias" which is the original "rodata=on"
3.) Add more comment for arch_parse_debug_rodata(),
update kernel-parameters.txt.
After this patch, the rodata=on will be the default.
Signed-off-by: Huang Shijie <shijie@os.amperecomputing.com>
---
.../admin-guide/kernel-parameters.txt | 2 +-
arch/arm64/include/asm/setup.h | 25 +++++++++++++++++--
2 files changed, 24 insertions(+), 3 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index a22b7e621007..51bce7b9d805 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5901,7 +5901,7 @@
rodata= [KNL,EARLY]
on Mark read-only kernel memory as read-only (default).
off Leave read-only kernel memory writable for debugging.
- full Mark read-only kernel memory and aliases as read-only
+ noalias Use more block mappings,may have better performance.
[arm64]
rockchip.usb_uart
diff --git a/arch/arm64/include/asm/setup.h b/arch/arm64/include/asm/setup.h
index ba269a7a3201..b3063326b79a 100644
--- a/arch/arm64/include/asm/setup.h
+++ b/arch/arm64/include/asm/setup.h
@@ -13,6 +13,27 @@
extern phys_addr_t __fdt_pointer __initdata;
extern u64 __cacheline_aligned boot_args[4];
+/*
+ * rodata=on (default):
+ * Apply read-only attributes of VM areas to the linear alias of
+ * the backing pages as well. This prevents code or read-only data
+ * from being modified (inadvertently or intentionally) via another
+ * mapping of the same memory page.
+ *
+ * This requires the linear region to be mapped down to pages,
+ * which may adversely affect performance in some cases.
+ *
+ * rodata=off:
+ * It provides us more block mappings and contiguous hits
+ * to map the linear region which minimize the TLB footprint.
+ * Leave read-only kernel memory writable for debugging.
+ *
+ * rodata=noalias:
+ * It provides us more block mappings and contiguous hits
+ * to map the linear region which minimize the TLB footprint.
+ * And the linear aliases of pages belonging to read-only mappings
+ * in vmalloc region are also marked as read-only.
+ */
static inline bool arch_parse_debug_rodata(char *arg)
{
extern bool rodata_enabled;
@@ -21,7 +42,7 @@ static inline bool arch_parse_debug_rodata(char *arg)
if (!arg)
return false;
- if (!strcmp(arg, "full")) {
+ if (!strcmp(arg, "on")) {
rodata_enabled = rodata_full = true;
return true;
}
@@ -31,7 +52,7 @@ static inline bool arch_parse_debug_rodata(char *arg)
return true;
}
- if (!strcmp(arg, "on")) {
+ if (!strcmp(arg, "noalias")) {
rodata_enabled = true;
rodata_full = false;
return true;
--
2.40.1Hello Huang,
On 12/9/24 12:50, Huang Shijie wrote:
>>From Documentation/admin-guide/kernel-parameters.txt:
> rodata= [KNL,EARLY]
> on Mark read-only kernel memory as read-only (default).
>
> So "rodata=on" is the default.
>
> But the current code does not follow the document, it makes "rodata=full"
> as the default.
>
> This patch refactors the "rodata=xxx" :
> 1.) Make rodata=on behaviour be the original rodata=full.
> (Drop the original rodata=full.)
> 2.) Introduce "rodata=noalias" which is the original "rodata=on"
> 3.) Add more comment for arch_parse_debug_rodata(),
> update kernel-parameters.txt.
>
> After this patch, the rodata=on will be the default.
Could this commit message be reworded/reformatted something like the
following instead ? Although feel free to improve this as required.
-----------------------------------------------------------------------
As per admin guide documentation, "rodata=on" should be the default on
platforms. Documentation/admin-guide/kernel-parameters.txt describes
these options as
rodata= [KNL,EARLY]
on Mark read-only kernel memory as read-only (default).
off Leave read-only kernel memory writable for debugging.
full Mark read-only kernel memory and aliases as read-only
[arm64]
But on arm64 platform, "rodata=full" is the default instead. This patch
implements the following changes.
- Make "rodata=on" behaviour same as the original "rodata=full"
- Make "rodata=noalias" (new) behaviour same as the original "rodata=on"
- Drop the original "rodata=full"
- Add comment for arch_parse_debug_rodata()
- Update kernel-parameters.txt as required
After this patch, the "rodata=on" will be the default on arm64 platform
as well.
-----------------------------------------------------------------------
>
> Signed-off-by: Huang Shijie <shijie@os.amperecomputing.com>
> ---
> .../admin-guide/kernel-parameters.txt | 2 +-
> arch/arm64/include/asm/setup.h | 25 +++++++++++++++++--
> 2 files changed, 24 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index a22b7e621007..51bce7b9d805 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -5901,7 +5901,7 @@
> rodata= [KNL,EARLY]
> on Mark read-only kernel memory as read-only (default).
> off Leave read-only kernel memory writable for debugging.
> - full Mark read-only kernel memory and aliases as read-only
> + noalias Use more block mappings,may have better performance.
> [arm64]
>
> rockchip.usb_uart
> diff --git a/arch/arm64/include/asm/setup.h b/arch/arm64/include/asm/setup.h
> index ba269a7a3201..b3063326b79a 100644
> --- a/arch/arm64/include/asm/setup.h
> +++ b/arch/arm64/include/asm/setup.h
> @@ -13,6 +13,27 @@
> extern phys_addr_t __fdt_pointer __initdata;
> extern u64 __cacheline_aligned boot_args[4];
>
> +/*
> + * rodata=on (default):
> + * Apply read-only attributes of VM areas to the linear alias of
> + * the backing pages as well. This prevents code or read-only data
> + * from being modified (inadvertently or intentionally) via another
> + * mapping of the same memory page.
> + *
> + * This requires the linear region to be mapped down to pages,
> + * which may adversely affect performance in some cases.
> + *
> + * rodata=off:
> + * It provides us more block mappings and contiguous hits
> + * to map the linear region which minimize the TLB footprint.
> + * Leave read-only kernel memory writable for debugging.
> + *
> + * rodata=noalias:
> + * It provides us more block mappings and contiguous hits
> + * to map the linear region which minimize the TLB footprint.
> + * And the linear aliases of pages belonging to read-only mappings
> + * in vmalloc region are also marked as read-only.
> + */
Reformatted and cleaned up the above comment a bit but feel free to
improve it further.
/*
* rodata=on (default)
*
* This applies read-only attributes to VM areas and to the linear
* alias of the backing pages as well. This prevents code or read-
* only data from being modified (inadvertently or intentionally),
* via another mapping for the same memory page.
*
* But this might cause linear map region to be mapped down to base
* pages, which may adversely affect performance in some cases.
*
* rodata=off
*
* This provides more block mappings and contiguous hints for linear
* map region which would minimize TLB footprint. This also leaves
* read-only kernel memory writable for debugging.
*
* rodata=noalias
*
* This provides more block mappings and contiguous hints for linear
* map region which would minimize TLB footprint. Linear aliases of
* pages belonging to read-only mappings in vmalloc region are also
* marked as read-only.
> static inline bool arch_parse_debug_rodata(char *arg)
> {
> extern bool rodata_enabled;
> @@ -21,7 +42,7 @@ static inline bool arch_parse_debug_rodata(char *arg)
> if (!arg)
> return false;
>
> - if (!strcmp(arg, "full")) {
> + if (!strcmp(arg, "on")) {
> rodata_enabled = rodata_full = true;
> return true;
> }
> @@ -31,7 +52,7 @@ static inline bool arch_parse_debug_rodata(char *arg)
> return true;
> }
>
> - if (!strcmp(arg, "on")) {
> + if (!strcmp(arg, "noalias")) {
> rodata_enabled = true;
> rodata_full = false;
> return true;
On Tue, 10 Dec 2024 at 08:17, Anshuman Khandual <anshuman.khandual@arm.com> wrote: > ... > > Reformatted and cleaned up the above comment a bit but feel free to > improve it further. > > /* > * rodata=on (default) > * > * This applies read-only attributes to VM areas and to the linear > * alias of the backing pages as well. This prevents code or read- > * only data from being modified (inadvertently or intentionally), > * via another mapping for the same memory page. > * > * But this might cause linear map region to be mapped down to base > * pages, which may adversely affect performance in some cases. > * > * rodata=off > * > * This provides more block mappings and contiguous hints for linear > * map region which would minimize TLB footprint. This also leaves > * read-only kernel memory writable for debugging. > * > * rodata=noalias > * > * This provides more block mappings and contiguous hints for linear > * map region which would minimize TLB footprint. Linear aliases of > * pages belonging to read-only mappings in vmalloc region are also > * marked as read-only. > If linear aliases are marked as read-only, how does 'noalias' differ from 'on'?
On 12/10/24 12:51, Ard Biesheuvel wrote: > On Tue, 10 Dec 2024 at 08:17, Anshuman Khandual > <anshuman.khandual@arm.com> wrote: >> > ... >> >> Reformatted and cleaned up the above comment a bit but feel free to >> improve it further. >> >> /* >> * rodata=on (default) >> * >> * This applies read-only attributes to VM areas and to the linear >> * alias of the backing pages as well. This prevents code or read- >> * only data from being modified (inadvertently or intentionally), >> * via another mapping for the same memory page. >> * >> * But this might cause linear map region to be mapped down to base >> * pages, which may adversely affect performance in some cases. >> * >> * rodata=off >> * >> * This provides more block mappings and contiguous hints for linear >> * map region which would minimize TLB footprint. This also leaves >> * read-only kernel memory writable for debugging. >> * >> * rodata=noalias >> * >> * This provides more block mappings and contiguous hints for linear >> * map region which would minimize TLB footprint. Linear aliases of >> * pages belonging to read-only mappings in vmalloc region are also >> * marked as read-only. >> > > If linear aliases are marked as read-only, how does 'noalias' differ from 'on'? Right, the last sentence can be can dropped.
On 2024/12/10 16:38, Anshuman Khandual wrote: > > On 12/10/24 12:51, Ard Biesheuvel wrote: >> On Tue, 10 Dec 2024 at 08:17, Anshuman Khandual >> <anshuman.khandual@arm.com> wrote: >> ... >>> Reformatted and cleaned up the above comment a bit but feel free to >>> improve it further. >>> >>> /* >>> * rodata=on (default) >>> * >>> * This applies read-only attributes to VM areas and to the linear >>> * alias of the backing pages as well. This prevents code or read- >>> * only data from being modified (inadvertently or intentionally), >>> * via another mapping for the same memory page. >>> * >>> * But this might cause linear map region to be mapped down to base >>> * pages, which may adversely affect performance in some cases. >>> * >>> * rodata=off >>> * >>> * This provides more block mappings and contiguous hints for linear >>> * map region which would minimize TLB footprint. This also leaves >>> * read-only kernel memory writable for debugging. >>> * >>> * rodata=noalias >>> * >>> * This provides more block mappings and contiguous hints for linear >>> * map region which would minimize TLB footprint. Linear aliases of >>> * pages belonging to read-only mappings in vmalloc region are also >>> * marked as read-only. >>> >> If linear aliases are marked as read-only, how does 'noalias' differ from 'on'? > Right, the last sentence can be can dropped. Okay, no problem. Thanks Huang Shijie
On Mon, 9 Dec 2024, Huang Shijie wrote:
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -5901,7 +5901,7 @@
> rodata= [KNL,EARLY]
> on Mark read-only kernel memory as read-only (default).
> off Leave read-only kernel memory writable for debugging.
> - full Mark read-only kernel memory and aliases as read-only
> + noalias Use more block mappings,may have better performance.
> [arm64]
Maybe use
noalias Do not check aliases in order to allow larger kernel page
sizes on a platforms without FEAT_BBM2 support[arm64])
instead?
>
> rockchip.usb_uart
> diff --git a/arch/arm64/include/asm/setup.h b/arch/arm64/include/asm/setup.h
> index ba269a7a3201..b3063326b79a 100644
> --- a/arch/arm64/include/asm/setup.h
> +++ b/arch/arm64/include/asm/setup.h
> @@ -13,6 +13,27 @@
> extern phys_addr_t __fdt_pointer __initdata;
> extern u64 __cacheline_aligned boot_args[4];
>
> +/*
> + * rodata=on (default):
> + * Apply read-only attributes of VM areas to the linear alias of
> + * the backing pages as well. This prevents code or read-only data
> + * from being modified (inadvertently or intentionally) via another
> + * mapping of the same memory page.
> + *
> + * This requires the linear region to be mapped down to pages,
> + * which may adversely affect performance in some cases.
> + *
> + * rodata=off:
> + * It provides us more block mappings and contiguous hits
> + * to map the linear region which minimize the TLB footprint.
> + * Leave read-only kernel memory writable for debugging.
> + *
> + * rodata=noalias:
> + * It provides us more block mappings and contiguous hits
> + * to map the linear region which minimize the TLB footprint.
> + * And the linear aliases of pages belonging to read-only mappings
> + * in vmalloc region are also marked as read-only.
> + */
> static inline bool arch_parse_debug_rodata(char *arg)
> {
> extern bool rodata_enabled;
> @@ -21,7 +42,7 @@ static inline bool arch_parse_debug_rodata(char *arg)
> if (!arg)
> return false;
>
> - if (!strcmp(arg, "full")) {
> + if (!strcmp(arg, "on")) {
> rodata_enabled = rodata_full = true;
> return true;
> }
> @@ -31,7 +52,7 @@ static inline bool arch_parse_debug_rodata(char *arg)
> return true;
> }
>
> - if (!strcmp(arg, "on")) {
> + if (!strcmp(arg, "noalias")) {
> rodata_enabled = true;
> rodata_full = false;
> return true;
>
On 2024/12/10 1:05, Christoph Lameter (Ampere) wrote: >> --- a/Documentation/admin-guide/kernel-parameters.txt >> +++ b/Documentation/admin-guide/kernel-parameters.txt >> @@ -5901,7 +5901,7 @@ >> rodata= [KNL,EARLY] >> on Mark read-only kernel memory as read-only (default). >> off Leave read-only kernel memory writable for debugging. >> - full Mark read-only kernel memory and aliases as read-only >> + noalias Use more block mappings,may have better performance. >> [arm64] > Maybe use > noalias Do not check aliases in order to allow larger kernel page > sizes on a platforms without FEAT_BBM2 support[arm64]) > > instead? The "rodata=noalias" here is equal to original "rodata=on". But Yang Shi's patch set works with original "rodata=full" : https://lists.infradead.org/pipermail/linux-arm-kernel/2024-November/979770.html IMHO, it's not proper to mention the FEAT_BBM in "rodata=noalias". Thanks Huang Shijie
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