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SubjectRe: [PATCH 00/23] KAISER: unmap most of the kernel from userspace page tables
On Wed, Nov 01, 2017 at 03:14:11PM -0700, Dave Hansen wrote:
> On 11/01/2017 01:54 AM, Ingo Molnar wrote:
> > Beyond the inevitable cavalcade of (solvable) problems that will pop up during
> > review, one major item I'd like to see addressed is runtime configurability: it
> > should be possible to switch between a CR3-flushing and a regular syscall and page
> > table model on the admin level, without restarting the kernel and apps. Distros
> > really, really don't want to double the number of kernel variants they have.
> >
> > The 'Kaiser off' runtime switch doesn't have to be as efficient as
> > CONFIG_KAISER=n, at least initialloy, but at minimum it should avoid the most
> > expensive page table switching paths in the syscall entry codepaths.
>
> Due to popular demand, I went and implemented this today. It's not the
> prettiest code I ever wrote, but it's pretty small.
>
> Just in case anyone wants to play with it, I threw a snapshot of it up here:
>
> > https://git.kernel.org/pub/scm/linux/kernel/git/daveh/x86-kaiser.git/log/?h=kaiser-dynamic-414rc6-20171101
>
> I ran some quick tests. When CONFIG_KAISER=y, but "echo 0 >
> kaiser-enabled", the tests that I ran were within the noise vs. a
> vanilla kernel, and that's with *zero* optimization.

It doesn't compile with KASLR enabled :P

Fixup:

diff --git a/arch/x86/boot/compressed/pagetable.c b/arch/x86/boot/compressed/pagetable.c
index f1aa43854bed..7be5fdd77a3f 100644
--- a/arch/x86/boot/compressed/pagetable.c
+++ b/arch/x86/boot/compressed/pagetable.c
@@ -35,6 +35,10 @@
/* Used by pgtable.h asm code to force instruction serialization. */
unsigned long __force_order;

+#ifdef CONFIG_KAISER
+int kaiser_enabled = 1;
+#endif
+
/* Used to track our page table allocation area. */
struct alloc_pgt_data {
unsigned char *pgt_buf;
--
Kirill A. Shutemov
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