Re: [PATCH v15 00/23] Generic page walk and ptdump

[Steven Price]

On 06/11/2019 13:31, Qian Cai wrote:
> > On Nov 4, 2019, at 2:35 PM, Qian Cai <cai@xxxxxx> wrote:
> >
> > On Fri, 2019-11-01 at 14:09 +0000, Steven Price wrote:
[...]
> > > Changes since v14:
> > > https://lore.kernel.org/lkml/20191028135910.33253-1-steven.price@xxxxxxx/
> > > * 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;
 		}