Hi Geert,
On 21/4/22 00:44, Geert Uytterhoeven wrote:
On Wed, Apr 20, 2022 at 3:53 PM Greg Ungerer <gerg@xxxxxxxxxxxxxx> wrote:
On 16/4/22 10:58, Hugh Dickins wrote:
Just to wrap up this thread: the tentative arch/ patches below did not
go into 5.18-rc2, but 5.18-rc3 will contain
1bdec44b1eee ("tmpfs: fix regressions from wider use of ZERO_PAGE")
which fixes a further issue, and deletes the line which gave you trouble.
With arch/h8300 removed from linux-next, and arch/arm losing a page by
the patch below, I don't think it's worth my arguing for those changes.
I'd still prefer arch/m68k to expose its empty_zero_page in ZERO_PAGE(),
or else not allocate it; but I won't be pursuing this further.
Thanks for pointing this out. It certainly does look wrong to me for
the m68k nommu case. I am not aware of any existing issues caused by
this - but there is no good reason not to fix it.
So I propose this change. Build and run tested on my m68knommu targets.
Regards
Greg
From f809fb8fbca9e5e637b8fda380955bd799bb3926 Mon Sep 17 00:00:00 2001
From: Greg Ungerer <gerg@xxxxxxxxxxxxxx>
Date: Wed, 20 Apr 2022 23:27:47 +1000
Subject: [PATCH] m68knommu: set ZERO_PAGE() allocated zeroed page
The non-MMU m68k pagetable ZERO_PAGE() macro is being set to the
somewhat non-sensical value of "virt_to_page(0)". The zeroth page
is not in any way guaranteed to be a page full of "0". So the result
is that ZERO_PAGE() will almost certainly contain random values.
We already allocate a real "empty_zero_page" in the mm setup code shared
between MMU m68k and non-MMU m68k. It is just not hooked up to the
ZERO_PAGE() macro for the non-MMU m68k case.
Fix ZERO_PAGE() to use the allocated "empty_zero_page" pointer.
I am not aware of any specific issues caused by the old code.
Link: https://lore.kernel.org/linux-m68k/2a462b23-5b8e-bbf4-ec7d-778434a3b9d7@xxxxxxxxxx/T/#t
Reported-by: Hugh Dickens <hughd@xxxxxxxxxx>
Signed-off-by: Greg Ungerer <gerg@xxxxxxxxxxxxxx>
---
arch/m68k/include/asm/pgtable_no.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/m68k/include/asm/pgtable_no.h b/arch/m68k/include/asm/pgtable_no.h
index 87151d67d91e..bce5ca56c388 100644
--- a/arch/m68k/include/asm/pgtable_no.h
+++ b/arch/m68k/include/asm/pgtable_no.h
@@ -42,7 +42,8 @@ extern void paging_init(void);
* ZERO_PAGE is a global shared page that is always zero: used
* for zero-mapped memory areas etc..
*/
-#define ZERO_PAGE(vaddr) (virt_to_page(0))
+extern void *empty_zero_page;
+#define ZERO_PAGE(vaddr) (virt_to_page(empty_zero_page))
/*
* All 32bit addresses are effectively valid for vmalloc...
And after that (or combined with this?), this can be factored
out from arch/m68k/include/asm/pgtable_{mm,no}.h into
arch/m68k/include/asm/pgtable.h.
I think a new patch to do that work on top of this one would be best.
I will work on that.
Regards
Greg
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
