On Fri, Aug 07, 2020 at 10:40:13AM +0200, Joerg Roedel wrote:
> From: Joerg Roedel <jroe...@suse.de>
>
> The code for preallocate_vmalloc_pages() was written under the
> assumption that the p4d_offset() and pud_offset() functions will perform
> present checks before dereferencing the parent entries.
>
> This assumption is wrong an leads to a bug in the code which causes the
> physical address found in the PGD be used as a page-table page, even if
> the PGD is not present.
>
> So the code flow currently is:
>
> pgd = pgd_offset_k(addr);
> p4d = p4d_offset(pgd, addr);
> if (p4d_none(*p4d))
> p4d = p4d_alloc(&init_mm, pgd, addr);
>
> This lacks a check for pgd_none() at least, the correct flow would be:
>
> pgd = pgd_offset_k(addr);
> if (pgd_none(*pgd))
> p4d = p4d_alloc(&init_mm, pgd, addr);
> else
> p4d = p4d_offset(pgd, addr);
>
> But this is the same flow that the p4d_alloc() and the pud_alloc()
> functions use internally, so there is no need to duplicate them.
>
> Remove the p?d_none() checks from the function and just call into
> p4d_alloc() and pud_alloc() to correctly pre-allocate the PGD entries.
>
> Reported-by: Jason A. Donenfeld <ja...@zx2c4.com>
> Fixes: 6eb82f994026 ("x86/mm: Pre-allocate P4D/PUD pages for vmalloc area")
> Signed-off-by: Joerg Roedel <jroe...@suse.de>
LGTM,
Reviewed-by: Mike Rapoport <r...@linux.ibm.com>
> ---
> arch/x86/mm/init_64.c | 31 +++++++++++++------------------
> 1 file changed, 13 insertions(+), 18 deletions(-)
>
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index 3f4e29a78f2b..449e071240e1 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -1253,28 +1253,23 @@ static void __init preallocate_vmalloc_pages(void)
> p4d_t *p4d;
> pud_t *pud;
>
> - p4d = p4d_offset(pgd, addr);
> - if (p4d_none(*p4d)) {
> - /* Can only happen with 5-level paging */
> - p4d = p4d_alloc(&init_mm, pgd, addr);
> - if (!p4d) {
> - lvl = "p4d";
> - goto failed;
> - }
> - }
> + lvl = "p4d";
> + p4d = p4d_alloc(&init_mm, pgd, addr);
> + if (!p4d)
> + goto failed;
>
> + /*
> + * With 5-level paging the P4D level is not folded. So the PGDs
> + * are now populated and there is no need to walk down to the
> + * PUD level.
> + */
> if (pgtable_l5_enabled())
> continue;
>
> - pud = pud_offset(p4d, addr);
> - if (pud_none(*pud)) {
> - /* Ends up here only with 4-level paging */
> - pud = pud_alloc(&init_mm, p4d, addr);
> - if (!pud) {
> - lvl = "pud";
> - goto failed;
> - }
> - }
> + lvl = "pud";
> + pud = pud_alloc(&init_mm, p4d, addr);
> + if (!pud)
> + goto failed;
> }
>
> return;
> --
> 2.26.2
>
--
Sincerely yours,
Mike.
