| Message ID | 1487498660-16600-1-git-send-email-hoeun.ryu@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 19 February 2017 at 10:04, Hoeun Ryu <hoeun.ryu@gmail.com> wrote: > After `__ro_after_init` marker is included in kernel, many kernel data > objects can be read-only-after-init. But there are many other places that > would be good to read-only-after-init but `__ro_after_init` can not be simply > applicable to them because they should be writable at some points, which are > during module_init/exit or dynamic de/registration for a specific subsystem. > `__ro_mostly_after_init` is basically the same to `__ro_after_init`. The > section is mapped as read-only after kernel init. The different thing is > this section is temporarily mapped as read-write during module_init/exit and > de/registration of a subsystem using set_ro_mostly_after_init_rw/ro pair. > Use `__ro_mostly_after_init` as a way to mark such memory instead when > `__ro_after_init` is not applicable because the memory should be writable > at the described points of time. They are read-only right after kernel init > and writable temporarily only during module_init/exit and dynamic > de/registration for a subsystem. > > Signed-off-by: Hoeun Ryu <hoeun.ryu@gmail.com> > --- > include/asm-generic/sections.h | 1 + > include/asm-generic/vmlinux.lds.h | 10 ++++++++++ > include/linux/cache.h | 11 +++++++++++ > 3 files changed, 22 insertions(+) > > diff --git a/include/asm-generic/sections.h b/include/asm-generic/sections.h > index 4df64a1..16a6f21 100644 > --- a/include/asm-generic/sections.h > +++ b/include/asm-generic/sections.h > @@ -34,6 +34,7 @@ extern char __bss_start[], __bss_stop[]; > extern char __init_begin[], __init_end[]; > extern char _sinittext[], _einittext[]; > extern char __start_data_ro_after_init[], __end_data_ro_after_init[]; > +extern char __start_data_ro_mostly_after_init[], __end_data_ro_mostly_after_init[]; > extern char _end[]; > extern char __per_cpu_load[], __per_cpu_start[], __per_cpu_end[]; > extern char __kprobes_text_start[], __kprobes_text_end[]; > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h > index 4e09b28..cc5f44e 100644 > --- a/include/asm-generic/vmlinux.lds.h > +++ b/include/asm-generic/vmlinux.lds.h > @@ -265,6 +265,15 @@ > __end_data_ro_after_init = .; > #endif > > +#ifndef RO_MOSTLY_AFTER_INIT_DATA > +#define RO_MOSTLY_AFTER_INIT_DATA(align) \ > + . = ALIGN(align); \ > + VMLINUX_SYMBOL(__start_data_ro_mostly_after_init) = .; \ > + *(.data..ro_mostly_after_init) \ > + . = ALIGN(align); \ > + VMLINUX_SYMBOL(__end_data_ro_mostly_after_init) = .; > +#endif > + > /* > * Read only Data > */ > @@ -275,6 +284,7 @@ > *(.rodata) *(.rodata.*) \ > RO_AFTER_INIT_DATA /* Read only after init */ \ > KEEP(*(__vermagic)) /* Kernel version magic */ \ > + RO_MOSTLY_AFTER_INIT_DATA(align) \ You can't really drop this in the middle of a section like this. On arm64, we try very hard to use a minimal segment alignment of 64 KB (of 2 MB if DEBUG_ALIGN_RODATA=y), to ensure that the TLB footprint of the kernel image is minimized. So this should be a separate section in the arm64 linker script. > . = ALIGN(8); \ > VMLINUX_SYMBOL(__start___tracepoints_ptrs) = .; \ > KEEP(*(__tracepoints_ptrs)) /* Tracepoints: pointer array */ \ > diff --git a/include/linux/cache.h b/include/linux/cache.h > index 1be04f8..fd1cb9b 100644 > --- a/include/linux/cache.h > +++ b/include/linux/cache.h > @@ -30,6 +30,17 @@ > #define __ro_after_init __attribute__((__section__(".data..ro_after_init"))) > #endif > > +/* > + * __ro_mostly_after_init is almost like __ro_after_init. > + * but __ro_mostly_after_init section is temporarily writable only during > + * module_init/exit or dynamic de/registeration of a subsystem using > + * set_ro_mostly_after_init_rw/ro pair. > + */ > +#ifndef __ro_mostly_after_init > +#define __ro_mostly_after_init \ > + __attribute__((__section__(".data..ro_mostly_after_init"))) > +#endif > + > #ifndef ____cacheline_aligned > #define ____cacheline_aligned __attribute__((__aligned__(SMP_CACHE_BYTES))) > #endif > -- > 2.7.4 >
> On 19 Feb 2017, at 8:24 PM, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote: > > On 19 February 2017 at 10:04, Hoeun Ryu <hoeun.ryu@gmail.com> wrote: >> After `__ro_after_init` marker is included in kernel, many kernel data >> objects can be read-only-after-init. But there are many other places that >> would be good to read-only-after-init but `__ro_after_init` can not be simply >> applicable to them because they should be writable at some points, which are >> during module_init/exit or dynamic de/registration for a specific subsystem. >> `__ro_mostly_after_init` is basically the same to `__ro_after_init`. The >> section is mapped as read-only after kernel init. The different thing is >> this section is temporarily mapped as read-write during module_init/exit and >> de/registration of a subsystem using set_ro_mostly_after_init_rw/ro pair. >> Use `__ro_mostly_after_init` as a way to mark such memory instead when >> `__ro_after_init` is not applicable because the memory should be writable >> at the described points of time. They are read-only right after kernel init >> and writable temporarily only during module_init/exit and dynamic >> de/registration for a subsystem. >> >> Signed-off-by: Hoeun Ryu <hoeun.ryu@gmail.com> >> --- >> include/asm-generic/sections.h | 1 + >> include/asm-generic/vmlinux.lds.h | 10 ++++++++++ >> include/linux/cache.h | 11 +++++++++++ >> 3 files changed, 22 insertions(+) >> >> diff --git a/include/asm-generic/sections.h b/include/asm-generic/sections.h >> index 4df64a1..16a6f21 100644 >> --- a/include/asm-generic/sections.h >> +++ b/include/asm-generic/sections.h >> @@ -34,6 +34,7 @@ extern char __bss_start[], __bss_stop[]; >> extern char __init_begin[], __init_end[]; >> extern char _sinittext[], _einittext[]; >> extern char __start_data_ro_after_init[], __end_data_ro_after_init[]; >> +extern char __start_data_ro_mostly_after_init[], __end_data_ro_mostly_after_init[]; >> extern char _end[]; >> extern char __per_cpu_load[], __per_cpu_start[], __per_cpu_end[]; >> extern char __kprobes_text_start[], __kprobes_text_end[]; >> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h >> index 4e09b28..cc5f44e 100644 >> --- a/include/asm-generic/vmlinux.lds.h >> +++ b/include/asm-generic/vmlinux.lds.h >> @@ -265,6 +265,15 @@ >> __end_data_ro_after_init = .; >> #endif >> >> +#ifndef RO_MOSTLY_AFTER_INIT_DATA >> +#define RO_MOSTLY_AFTER_INIT_DATA(align) \ >> + . = ALIGN(align); \ >> + VMLINUX_SYMBOL(__start_data_ro_mostly_after_init) = .; \ >> + *(.data..ro_mostly_after_init) \ >> + . = ALIGN(align); \ >> + VMLINUX_SYMBOL(__end_data_ro_mostly_after_init) = .; >> +#endif >> + >> /* >> * Read only Data >> */ >> @@ -275,6 +284,7 @@ >> *(.rodata) *(.rodata.*) \ >> RO_AFTER_INIT_DATA /* Read only after init */ \ >> KEEP(*(__vermagic)) /* Kernel version magic */ \ >> + RO_MOSTLY_AFTER_INIT_DATA(align) \ > > You can't really drop this in the middle of a section like this. On > arm64, we try very hard to use a minimal segment alignment of 64 KB > (of 2 MB if DEBUG_ALIGN_RODATA=y), to ensure that the TLB footprint of > the kernel image is minimized. > > So this should be a separate section in the arm64 linker script. > Could we achieve that using ALIGN(SECTION_SIZE) not ALIGN(PAGE_SIZE) for RO_DATA ? >> . = ALIGN(8); \ >> VMLINUX_SYMBOL(__start___tracepoints_ptrs) = .; \ >> KEEP(*(__tracepoints_ptrs)) /* Tracepoints: pointer array */ \ >> diff --git a/include/linux/cache.h b/include/linux/cache.h >> index 1be04f8..fd1cb9b 100644 >> --- a/include/linux/cache.h >> +++ b/include/linux/cache.h >> @@ -30,6 +30,17 @@ >> #define __ro_after_init __attribute__((__section__(".data..ro_after_init"))) >> #endif >> >> +/* >> + * __ro_mostly_after_init is almost like __ro_after_init. >> + * but __ro_mostly_after_init section is temporarily writable only during >> + * module_init/exit or dynamic de/registeration of a subsystem using >> + * set_ro_mostly_after_init_rw/ro pair. >> + */ >> +#ifndef __ro_mostly_after_init >> +#define __ro_mostly_after_init \ >> + __attribute__((__section__(".data..ro_mostly_after_init"))) >> +#endif >> + >> #ifndef ____cacheline_aligned >> #define ____cacheline_aligned __attribute__((__aligned__(SMP_CACHE_BYTES))) >> #endif >> -- >> 2.7.4
diff --git a/include/asm-generic/sections.h b/include/asm-generic/sections.h index 4df64a1..16a6f21 100644 --- a/include/asm-generic/sections.h +++ b/include/asm-generic/sections.h @@ -34,6 +34,7 @@ extern char __bss_start[], __bss_stop[]; extern char __init_begin[], __init_end[]; extern char _sinittext[], _einittext[]; extern char __start_data_ro_after_init[], __end_data_ro_after_init[]; +extern char __start_data_ro_mostly_after_init[], __end_data_ro_mostly_after_init[]; extern char _end[]; extern char __per_cpu_load[], __per_cpu_start[], __per_cpu_end[]; extern char __kprobes_text_start[], __kprobes_text_end[]; diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h index 4e09b28..cc5f44e 100644 --- a/include/asm-generic/vmlinux.lds.h +++ b/include/asm-generic/vmlinux.lds.h @@ -265,6 +265,15 @@ __end_data_ro_after_init = .; #endif +#ifndef RO_MOSTLY_AFTER_INIT_DATA +#define RO_MOSTLY_AFTER_INIT_DATA(align) \ + . = ALIGN(align); \ + VMLINUX_SYMBOL(__start_data_ro_mostly_after_init) = .; \ + *(.data..ro_mostly_after_init) \ + . = ALIGN(align); \ + VMLINUX_SYMBOL(__end_data_ro_mostly_after_init) = .; +#endif + /* * Read only Data */ @@ -275,6 +284,7 @@ *(.rodata) *(.rodata.*) \ RO_AFTER_INIT_DATA /* Read only after init */ \ KEEP(*(__vermagic)) /* Kernel version magic */ \ + RO_MOSTLY_AFTER_INIT_DATA(align) \ . = ALIGN(8); \ VMLINUX_SYMBOL(__start___tracepoints_ptrs) = .; \ KEEP(*(__tracepoints_ptrs)) /* Tracepoints: pointer array */ \ diff --git a/include/linux/cache.h b/include/linux/cache.h index 1be04f8..fd1cb9b 100644 --- a/include/linux/cache.h +++ b/include/linux/cache.h @@ -30,6 +30,17 @@ #define __ro_after_init __attribute__((__section__(".data..ro_after_init"))) #endif +/* + * __ro_mostly_after_init is almost like __ro_after_init. + * but __ro_mostly_after_init section is temporarily writable only during + * module_init/exit or dynamic de/registeration of a subsystem using + * set_ro_mostly_after_init_rw/ro pair. + */ +#ifndef __ro_mostly_after_init +#define __ro_mostly_after_init \ + __attribute__((__section__(".data..ro_mostly_after_init"))) +#endif + #ifndef ____cacheline_aligned #define ____cacheline_aligned __attribute__((__aligned__(SMP_CACHE_BYTES))) #endif
After `__ro_after_init` marker is included in kernel, many kernel data objects can be read-only-after-init. But there are many other places that would be good to read-only-after-init but `__ro_after_init` can not be simply applicable to them because they should be writable at some points, which are during module_init/exit or dynamic de/registration for a specific subsystem. `__ro_mostly_after_init` is basically the same to `__ro_after_init`. The section is mapped as read-only after kernel init. The different thing is this section is temporarily mapped as read-write during module_init/exit and de/registration of a subsystem using set_ro_mostly_after_init_rw/ro pair. Use `__ro_mostly_after_init` as a way to mark such memory instead when `__ro_after_init` is not applicable because the memory should be writable at the described points of time. They are read-only right after kernel init and writable temporarily only during module_init/exit and dynamic de/registration for a subsystem. Signed-off-by: Hoeun Ryu <hoeun.ryu@gmail.com> --- include/asm-generic/sections.h | 1 + include/asm-generic/vmlinux.lds.h | 10 ++++++++++ include/linux/cache.h | 11 +++++++++++ 3 files changed, 22 insertions(+)