Messages in this thread Patch in this message | | | Subject | [PATCH] x86/kpti: WARN if kernel memory mapped to userspace is non-global | From | Dave Hansen <> | Date | Fri, 15 Dec 2017 16:01:45 -0800 |
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From: Dave Hansen <dave.hansen@linux.intel.com>
All memory being mapped out to userspace is shared. That means that it is both safe and _expected_ to have the page table Global bit set.
If a PMD is found without Global set, it either a place that could be performing better, or something unexpected is being mapped out to userspace. Both of those are things for which a warning is good.
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Andy Lutomirski <luto@kernel.org> Cc: Borislav Petkov <bp@suse.de> Cc: Brian Gerst <brgerst@gmail.com> Cc: Denys Vlasenko <dvlasenk@redhat.com> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Josh Poimboeuf <jpoimboe@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rik van Riel <riel@redhat.com> ---
b/arch/x86/mm/kpti.c | 3 +++ 1 file changed, 3 insertions(+)
diff -puN arch/x86/mm/kpti.c~kaiser-set-global-in-kernel-for-shared arch/x86/mm/kpti.c --- a/arch/x86/mm/kpti.c~kaiser-set-global-in-kernel-for-shared 2017-12-15 09:47:52.884717268 -0800 +++ b/arch/x86/mm/kpti.c 2017-12-15 10:00:39.134715357 -0800 @@ -157,6 +157,9 @@ kpti_clone_pmds(unsigned long start, uns if (WARN_ON(!target_pmd)) return; + /* Only clone PMDs which we *intend* to share: */ + WARN_ON_ONCE(!(pmd_flags(*target_pmd) & _PAGE_GLOBAL)); + /* * Copy the PMD. That is, the kernelmode and usermode * tables will share the last-level page tables of this _
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