lkml.org 
[lkml]   [2022]   [Dec]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[tip: x86/mm] x86/mm: Ensure forced page table splitting
The following commit has been merged into the x86/mm branch of tip:

Commit-ID: 3e844d842d49cdbe61a4b338bdd512654179488a
Gitweb: https://git.kernel.org/tip/3e844d842d49cdbe61a4b338bdd512654179488a
Author: Dave Hansen <dave.hansen@linux.intel.com>
AuthorDate: Fri, 18 Nov 2022 07:16:16 -08:00
Committer: Dave Hansen <dave.hansen@linux.intel.com>
CommitterDate: Thu, 15 Dec 2022 10:37:28 -08:00

x86/mm: Ensure forced page table splitting

There are a few kernel users like kfence that require 4k pages to work
correctly and do not support large mappings. They use set_memory_4k()
to break down those large mappings.

That, in turn relies on cpa_data->force_split option to indicate to
set_memory code that it should split page tables regardless of whether
the need to be.

But, a recent change added an optimization which would return early
if a set_memory request came in that did not change permissions. It
did not consult ->force_split and would mistakenly optimize away the
splitting that set_memory_4k() needs. This broke kfence.

Skip the same-permission optimization when ->force_split is set.

Fixes: 127960a05548 ("x86/mm: Inhibit _PAGE_NX changes from cpa_process_alias()")
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Tested-by: Marco Elver <elver@google.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/all/CA+G9fYuFxZTxkeS35VTZMXwQvohu73W3xbZ5NtjebsVvH6hCuA@mail.gmail.com/
---
arch/x86/mm/pat/set_memory.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index 220361c..0db6951 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -1727,7 +1727,8 @@ static int __change_page_attr_set_clr(struct cpa_data *cpa, int primary)
/*
* No changes, easy!
*/
- if (!(pgprot_val(cpa->mask_set) | pgprot_val(cpa->mask_clr)))
+ if (!(pgprot_val(cpa->mask_set) | pgprot_val(cpa->mask_clr)) &&
+ !cpa->force_split)
return ret;

while (rempages) {
\
 
 \ /
  Last update: 2022-12-17 19:55    [W:0.042 / U:0.352 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site