Re: [PATCH bpf-next v1 RESEND 5/5] x86: use register_text_tail_vm

["Edgecombe, Rick P" <rick.p.edgecombe@intel.com>]

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@kernel.org>
> ---
>  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);