On Mon, 2022-10-31 at 15:25 -0700, Song Liu wrote:
> Allocate 2MB pages up to round_up(_etext, 2MB), and register memory
> [round_up(_etext, 4kb), round_up(_etext, 2MB)] with
> register_text_tail_vm
> so that we can use this part of memory for dynamic kernel text (BPF
> programs, etc.).
>
> Here is an example:
>
> [root@eth50-1 ~]# grep _etext /proc/kallsyms
> ffffffff82202a08 T _etext
>
> [root@eth50-1 ~]# grep bpf_prog_ /proc/kallsyms | tail -n 3
> ffffffff8220f920 t
> bpf_prog_cc61a5364ac11d93_handle__sched_wakeup [bpf]
> ffffffff8220fa28 t
> bpf_prog_cc61a5364ac11d93_handle__sched_wakeup_new [bpf]
> ffffffff8220fad4 t
> bpf_prog_3bf73fa16f5e3d92_handle__sched_switch [bpf]
>
> [root@eth50-1 ~]# grep 0xffffffff82200000
> /sys/kernel/debug/page_tables/kernel
> 0xffffffff82200000-
> 0xffffffff82400000 2M ro PSE x pmd
>
> ffffffff82200000-ffffffff82400000 is a 2MB page, serving kernel text,
> and
> bpf programs.
>
> Signed-off-by: Song Liu <song@xxxxxxxxxx>
> ---
> arch/x86/include/asm/pgtable_64_types.h | 1 +
> arch/x86/mm/init_64.c | 4 +++-
> include/linux/vmalloc.h | 4 ++++
> 3 files changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/pgtable_64_types.h
> b/arch/x86/include/asm/pgtable_64_types.h
> index 04f36063ad54..c0f9cceb109a 100644
> --- a/arch/x86/include/asm/pgtable_64_types.h
> +++ b/arch/x86/include/asm/pgtable_64_types.h
> @@ -101,6 +101,7 @@ extern unsigned int ptrs_per_p4d;
> #define PUD_MASK (~(PUD_SIZE - 1))
> #define PGDIR_SIZE (_AC(1, UL) << PGDIR_SHIFT)
> #define PGDIR_MASK (~(PGDIR_SIZE - 1))
> +#define PMD_ALIGN(x) (((unsigned long)(x) + (PMD_SIZE - 1)) &
> PMD_MASK)
>
> /*
> * See Documentation/x86/x86_64/mm.rst for a description of the
> memory map.
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index 3f040c6e5d13..5b42fc0c6099 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -1373,7 +1373,7 @@ void mark_rodata_ro(void)
> unsigned long start = PFN_ALIGN(_text);
> unsigned long rodata_start = PFN_ALIGN(__start_rodata);
> unsigned long end = (unsigned long)__end_rodata_hpage_align;
> - unsigned long text_end = PFN_ALIGN(_etext);
> + unsigned long text_end = PMD_ALIGN(_etext);
> unsigned long rodata_end = PFN_ALIGN(__end_rodata);
> unsigned long all_end;
Check out is_errata93(). Right now it assumes all text is between text-
etext and MODULES_VADDR-MODULES_END. It's a quite old errata, but it
would be nice if we had a is_text_addr() helper or something. To help
keep track of the places where text might pop up.
Speaking of which, it might be nice to update
Documentation/x86/x86_64/mm.rst with some hints that this area exists.
>
> @@ -1414,6 +1414,8 @@ void mark_rodata_ro(void)
> (void *)rodata_end, (void *)_sdata);
>
> debug_checkwx();
> + register_text_tail_vm(PFN_ALIGN((unsigned long)_etext),
> + PMD_ALIGN((unsigned long)_etext));
> }
>
> int kern_addr_valid(unsigned long addr)
> diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
> index 9b2042313c12..7365cf9c4e7f 100644
> --- a/include/linux/vmalloc.h
> +++ b/include/linux/vmalloc.h
> @@ -132,11 +132,15 @@ extern void vm_unmap_aliases(void);
> #ifdef CONFIG_MMU
> extern void __init vmalloc_init(void);
> extern unsigned long vmalloc_nr_pages(void);
> +void register_text_tail_vm(unsigned long start, unsigned long end);
> #else
> static inline void vmalloc_init(void)
> {
> }
> static inline unsigned long vmalloc_nr_pages(void) { return 0; }
> +void register_text_tail_vm(unsigned long start, unsigned long end)
> +{
> +}
> #endif
This looks like it should be in the previous patch.
>
> extern void *vmalloc(unsigned long size) __alloc_size(1);
