Re: [RFC PATCH v1] mm/vmalloc: fix incorrect __vmap_pages_range_noflush() if vm_area_alloc_pages() from high order fallback to order0

[Barry Song <21cnbao@xxxxxxxxx>]

On Thu, Jul 25, 2024 at 6:19 AM <hailong.liu@xxxxxxxx> wrote:
>
> From: "Hailong.Liu" <hailong.liu@xxxxxxxx>
>
> The scenario where the issue occurs is as follows:
> CONFIG: vmap_allow_huge = true && 2M is for PMD_SIZE
> kvmalloc(2M)
>     __vmalloc_node_range(vm_flags=VM_ALLOW_HUGE_VMAP)
>         vm_area_alloc_pages(order=9) --->allocs order9 failed and fallback to order0
>                                         and phys_addr is aligned with PMD_SIZE
>             vmap_pages_range
>                 vmap_pages_range_noflush
>                     __vmap_pages_range_noflush(page_shift = 21) ----> incorrect vmap *huge* here
>
> Fix it by introducing VM_AREA_ALLOC_PAGES_FALLBACK in page->private if fallback to 0.
> Fixes: e9c3cda4d86e ("mm, vmalloc: fix high order __GFP_NOFAIL allocations")
>
> CC: Barry Song <21cnbao@xxxxxxxxx>
> Reported-by: Tangquan.Zheng <zhengtangquan@xxxxxxxx>
> Signed-off-by: Hailong.Liu <hailong.liu@xxxxxxxx>
> ---
>  mm/vmalloc.c | 14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 03c78fae06f3..b35dfd3eeee3 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -75,6 +75,8 @@ early_param("nohugevmalloc", set_nohugevmalloc);
>  static const bool vmap_allow_huge = false;
>  #endif /* CONFIG_HAVE_ARCH_HUGE_VMALLOC */
>
> +#define VM_AREA_ALLOC_PAGES_FALLBACK 0x1
> +
>  bool is_vmalloc_addr(const void *x)
>  {
>         unsigned long addr = (unsigned long)kasan_reset_tag(x);
> @@ -604,8 +606,13 @@ int __vmap_pages_range_noflush(unsigned long addr, unsigned long end,
>         WARN_ON(page_shift < PAGE_SHIFT);
>
>         if (!IS_ENABLED(CONFIG_HAVE_ARCH_HUGE_VMALLOC) ||
> -                       page_shift == PAGE_SHIFT)
> -               return vmap_small_pages_range_noflush(addr, end, prot, pages);
> +                       page_shift == PAGE_SHIFT ||
> +                       page_private(pages[0]) == VM_AREA_ALLOC_PAGES_FALLBACK) {
> +               int ret = vmap_small_pages_range_noflush(addr, end, prot, pages);
> +
> +               set_page_private(pages[0], 0);
> +               return ret;
> +       }

we could have more than one *serious* bug here? do we also need the below
if ((end -  start) % PMD_SIZE) != 0)  ? no ?

int __vmap_pages_range_noflush(unsigned long addr, unsigned long end,
                pgprot_t prot, struct page **pages, unsigned int page_shift)
{
        unsigned int i, nr = (end - addr) >> PAGE_SHIFT;

        WARN_ON(page_shift < PAGE_SHIFT);

        if (!IS_ENABLED(CONFIG_HAVE_ARCH_HUGE_VMALLOC) ||
                        page_shift == PAGE_SHIFT)
                return vmap_small_pages_range_noflush(addr, end, prot, pages);

        for (i = 0; i < nr; i += 1U << (page_shift - PAGE_SHIFT)) {
                int err;

                err = vmap_range_noflush(addr, addr + (1UL << page_shift),
                                        page_to_phys(pages[i]), prot,
                                        page_shift);
                if (err)
                        return err;

                addr += 1UL << page_shift;
        }

+        if (addr < end)
+                return vmap_small_pages_range_noflush(addr, end,
prot, pages + i);

        return 0;
}

>
>         for (i = 0; i < nr; i += 1U << (page_shift - PAGE_SHIFT)) {
>                 int err;
> @@ -3583,6 +3590,7 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
>
>                         /* fall back to the zero order allocations */
>                         alloc_gfp |= __GFP_NOFAIL;
> +                       fallback = true;
>                         order = 0;
>                         continue;
>                 }
> @@ -3608,6 +3616,8 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
>                 cond_resched();
>                 nr_allocated += 1U << order;
>         }
> +       if (nr_allocated && fallback)
> +               set_page_private(pages[0], VM_AREA_ALLOC_PAGES_FALLBACK);
>
>         return nr_allocated;
>  }
> --
> 2.34.1
>