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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. > Please mention RODATA_FULL_DEFAULT_ENABLED here. okay. >> This patch implements the following changes. >> >> - Make "rodata=on" behaviour same as the original "rodata=full" > You should mention that this gives us parity with x86. No problem. >> - 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 > These last two are self-evident from the code and don't need to be listed > here. > >> After this patch, the "rodata=on" will be the default on arm64 platform >> as well. >> >> Reviewed-by: Christoph Lameter (Ampere) >> Signed-off-by: Huang Shijie >> --- >> .../admin-guide/kernel-parameters.txt | 2 +- >> arch/arm64/include/asm/setup.h | 28 +++++++++++++++++-- >> 2 files changed, 27 insertions(+), 3 deletions(-) >> >> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt >> index ee0735c6b8e2..3590bdc8d9a5 100644 >> --- a/Documentation/admin-guide/kernel-parameters.txt >> +++ b/Documentation/admin-guide/kernel-parameters.txt >> @@ -6354,7 +6354,7 @@ >> 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] > This isn't particularly helpful documentation and I think we need to mention > the linear alias rather than talk about the page-table structure. > > How about: > > noalias Mark read-only kernel memory as read-only but retain > writable aliases in the direct map for regions outside > of the kernel image. [arm64] > > ? Okay, thanks. >> diff --git a/arch/arm64/include/asm/setup.h b/arch/arm64/include/asm/setup.h >> index ba269a7a3201..6b994d0881d1 100644 >> --- a/arch/arm64/include/asm/setup.h >> +++ b/arch/arm64/include/asm/setup.h >> @@ -13,6 +13,30 @@ >> extern phys_addr_t __fdt_pointer __initdata; >> extern u64 __cacheline_aligned boot_args[4]; >> >> +/* >> + * 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. This leaves the linear >> + * alias of read-only mappings in the vmalloc space writeable, making >> + * them susceptible to inadvertent modification by software. >> + */ > Please remove this comment. If you want to keep it, this information > belongs either in the commit message (to justify the performance impact) Okay, I can move it to commit message. Thanks Huang Shijie