Re: [PATCH 1/1] mm/vmalloc: Add preempt point in purge_vmap_node() when enabling kasan

[Uladzislau Rezki]

On Wed, Jul 24, 2024 at 08:46:24PM +0800, Adrian Huang wrote:
> > It works great and does not generate the soft-lock-up splat :)
> > See below some comments:
> 
> Great. Thanks for the confirmation.
> 
> <snip>
> 
> >> +     kasan_release_vmalloc(start, end, start, end, KASAN_VMALLOC_TLB_FLUSH);
> >> +
> >>
> > Do we need it here? We just did the TLB flush for en entire range in the
> > __purge_vmap_area_lazy(). So, it is two times invoked and looks odd to me.
> >
> > Am i missing something?
> 
> 1. The TLB flush for the entire range in __purge_vmap_area_lazy() is for
> the vmalloc virtual address (VMALLOC_START->VMALLOC_END).
> 
> 2. The TLB flush in purge_vmap_node() is for the KASAN shadow virtual address 
> (the shadow offset 'CONFIG_KASAN_SHADOW_OFFSET' is defined in .config).
> 
Correct. It deals with a shadow region!

>
> BTW, I found my first patch has the potential risk. We need to flush TLB of
> the KASAN shadow virtual address firstly. Please see the following patch for
> detail. (I put the comment in the following patch). The following patch
> also works well on my 256-core machine.
> 
I noticed that and it would be my second question :)

>
> If you're ok with the patch, I'll submit it for upstream review. And, may I
> have your tag(s): tested-by/reviewed-by? (If possible, could you please have
> a test for the following patch).
> 
I am OK. I will test and get back soon.

> Thanks.
> 
> ---
> diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> index 70d6a8f6e25d..ddbf42a1a7b7 100644
> --- a/include/linux/kasan.h
> +++ b/include/linux/kasan.h
> @@ -55,6 +55,9 @@ extern p4d_t kasan_early_shadow_p4d[MAX_PTRS_PER_P4D];
>  int kasan_populate_early_shadow(const void *shadow_start,
>  				const void *shadow_end);
>  
> +#define KASAN_VMALLOC_PAGE_RANGE 0x1 /* Apply exsiting page range */
> +#define KASAN_VMALLOC_TLB_FLUSH  0x2 /* TLB flush */
> +
>  #ifndef kasan_mem_to_shadow
>  static inline void *kasan_mem_to_shadow(const void *addr)
>  {
> @@ -511,7 +514,8 @@ void kasan_populate_early_vm_area_shadow(void *start, unsigned long size);
>  int kasan_populate_vmalloc(unsigned long addr, unsigned long size);
>  void kasan_release_vmalloc(unsigned long start, unsigned long end,
>  			   unsigned long free_region_start,
> -			   unsigned long free_region_end);
> +			   unsigned long free_region_end,
> +			   unsigned long flags);
>  
>  #else /* CONFIG_KASAN_GENERIC || CONFIG_KASAN_SW_TAGS */
>  
> @@ -526,7 +530,8 @@ static inline int kasan_populate_vmalloc(unsigned long start,
>  static inline void kasan_release_vmalloc(unsigned long start,
>  					 unsigned long end,
>  					 unsigned long free_region_start,
> -					 unsigned long free_region_end) { }
> +					 unsigned long free_region_end,
> +					 unsigned long flags) { }
>  
>  #endif /* CONFIG_KASAN_GENERIC || CONFIG_KASAN_SW_TAGS */
>  
> @@ -561,7 +566,8 @@ static inline int kasan_populate_vmalloc(unsigned long start,
>  static inline void kasan_release_vmalloc(unsigned long start,
>  					 unsigned long end,
>  					 unsigned long free_region_start,
> -					 unsigned long free_region_end) { }
> +					 unsigned long free_region_end,
> +					 unsigned long flags) { }
>  
>  static inline void *kasan_unpoison_vmalloc(const void *start,
>  					   unsigned long size,
> diff --git a/mm/kasan/shadow.c b/mm/kasan/shadow.c
> index d6210ca48dda..88d1c9dcb507 100644
> --- a/mm/kasan/shadow.c
> +++ b/mm/kasan/shadow.c
> @@ -489,7 +489,8 @@ static int kasan_depopulate_vmalloc_pte(pte_t *ptep, unsigned long addr,
>   */
>  void kasan_release_vmalloc(unsigned long start, unsigned long end,
>  			   unsigned long free_region_start,
> -			   unsigned long free_region_end)
> +			   unsigned long free_region_end,
> +			   unsigned long flags)
>  {
>  	void *shadow_start, *shadow_end;
>  	unsigned long region_start, region_end;
> @@ -522,12 +523,17 @@ void kasan_release_vmalloc(unsigned long start, unsigned long end,
>  			__memset(shadow_start, KASAN_SHADOW_INIT, shadow_end - shadow_start);
>  			return;
>  		}
> -		apply_to_existing_page_range(&init_mm,
> +
> +
> +		if (flags & KASAN_VMALLOC_PAGE_RANGE)
> +			apply_to_existing_page_range(&init_mm,
>  					     (unsigned long)shadow_start,
>  					     size, kasan_depopulate_vmalloc_pte,
>  					     NULL);
> -		flush_tlb_kernel_range((unsigned long)shadow_start,
> -				       (unsigned long)shadow_end);
> +
> +		if (flags & KASAN_VMALLOC_TLB_FLUSH)
> +			flush_tlb_kernel_range((unsigned long)shadow_start,
> +					       (unsigned long)shadow_end);
>  	}
>  }
>  
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index e34ea860153f..12cdc92cdb83 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2193,8 +2193,22 @@ static void purge_vmap_node(struct work_struct *work)
>  	struct vmap_area *va, *n_va;
>  	LIST_HEAD(local_list);
>  
> +	unsigned long start;
> +	unsigned long end;
> +
>  	vn->nr_purged = 0;
>  
> +	start = list_first_entry(&vn->purge_list, struct vmap_area, list)->va_start;
> +
> +	end = list_last_entry(&vn->purge_list, struct vmap_area, list)->va_end;
> +
> +	/*
> +	 * Since node_pool_add_va() returns vmap_area(s) to its pool, the
> +	 * returned vmap_area(s) might be grabbed immediately via node_alloc()
> +	 * by other core. We need to flush TLB firstly.
> +	 */
> +	kasan_release_vmalloc(start, end, start, end, KASAN_VMALLOC_TLB_FLUSH);
> +
>  	list_for_each_entry_safe(va, n_va, &vn->purge_list, list) {
>  		unsigned long nr = (va->va_end - va->va_start) >> PAGE_SHIFT;
>  		unsigned long orig_start = va->va_start;
> @@ -2205,7 +2219,8 @@ static void purge_vmap_node(struct work_struct *work)
>  
>  		if (is_vmalloc_or_module_addr((void *)orig_start))
>  			kasan_release_vmalloc(orig_start, orig_end,
> -					      va->va_start, va->va_end);
> +					      va->va_start, va->va_end,
> +					      KASAN_VMALLOC_PAGE_RANGE);
>  
>  		atomic_long_sub(nr, &vmap_lazy_nr);
>  		vn->nr_purged++;
> @@ -4726,7 +4741,8 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
>  				&free_vmap_area_list);
>  		if (va)
>  			kasan_release_vmalloc(orig_start, orig_end,
> -				va->va_start, va->va_end);
> +				va->va_start, va->va_end,
> +				KASAN_VMALLOC_PAGE_RANGE | KASAN_VMALLOC_TLB_FLUSH);
>  		vas[area] = NULL;
>  	}
>  
> @@ -4776,7 +4792,8 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
>  				&free_vmap_area_list);
>  		if (va)
>  			kasan_release_vmalloc(orig_start, orig_end,
> -				va->va_start, va->va_end);
> +				va->va_start, va->va_end,
> +				KASAN_VMALLOC_PAGE_RANGE | KASAN_VMALLOC_TLB_FLUSH);
>  		vas[area] = NULL;
>  		kfree(vms[area]);
>  	}