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

Uladzislau Rezki
2024-07-24T14:32:42Z

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]);
> }