On 06/11/2019 13:31, Qian Cai wrote:

quoted

On Nov 4, 2019, at 2:35 PM, Qian Cai [off-list ref] wrote:

On Fri, 2019-11-01 at 14:09 +0000, Steven Price wrote:

[...]

quoted

quoted

Changes since v14:
https://lore.kernel.org/lkml/20191028135910.33253-1-steven.price@arm.com/ (local)
* Switch walk_page_range() into two functions, the existing
   walk_page_range() now still requires VMAs (and treats areas without a
   VMA as a 'hole'). The new walk_page_range_novma() ignores VMAs and
   will report the actual page table layout. This fixes the previous
   breakage of /proc/<pid>/pagemap
* New patch at the end of the series which reduces the 'level' numbers
   by 1 to simplify the code slightly
* Added tags

Does this new version also take care of this boot crash seen with v14? Suppose
it is now breaking CONFIG_EFI_PGT_DUMP=y? The full config is,

https://raw.githubusercontent.com/cailca/linux-mm/master/x86.config

V15 is indeed DOA here.

Thanks for finding this, it looks like EFI causes issues here. The below fixes
this for me (booting in QEMU).

Andrew: do you want me to send out the entire series again for this fix, or
can you squash this into mm-pagewalk-allow-walking-without-vma.patch?

Thanks,

Steve

---8<---

diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index c7529dc4f82b..70dcaa23598f 100644
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c

@@ -90,7 +90,7 @@ static int walk_pmd_range(pud_t *pud, unsigned long addr, unsigned long end,
  			split_huge_pmd(walk->vma, pmd, addr);
  			if (pmd_trans_unstable(pmd))
  				goto again;
-		} else if (pmd_leaf(*pmd)) {
+		} else if (pmd_leaf(*pmd) || !pmd_present(*pmd)) {
  			continue;
  		}
  

@@ -141,7 +141,7 @@ static int walk_pud_range(p4d_t *p4d, unsigned long addr, unsigned long end,
  			split_huge_pud(walk->vma, pud, addr);
  			if (pud_none(*pud))
  				goto again;
-		} else if (pud_leaf(*pud)) {
+		} else if (pud_leaf(*pud) || !pud_present(*pud)) {
  			continue;
  		}
  

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