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

Uladzislau Rezki
2024-07-24T15:10:04Z

On Wed, Jul 24, 2024 at 04:32:37PM +0200, Uladzislau Rezki wrote:
> 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);
remove the space.
> >
> > + unsigned long start;
> > + unsigned long end;
> > +
> > vn->nr_purged = 0;
> >
> > + start = list_first_entry(&vn->purge_list, struct vmap_area, list)->va_start;
no need to have an extra space.
> > +
> > + 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);
>
orig_start and orig_end are unnecessary now. But it can be removed by
an extra patch!

> >
> > 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]);
> > }
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Tested-by: Uladzislau Rezki (Sony) <urezki@gmail.com>

Thank you.