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SubjectRe: CONFIG_PAGE_TABLE_ISOLATION=y on x86_64 causes gcc to segfault when building x86_32 binaries
On Wed, 3 Jan 2018, Thomas Gleixner wrote:

> On Wed, 3 Jan 2018, Lars Wendler wrote:
> > Am Wed, 3 Jan 2018 13:05:38 +0100 (CET)
> > schrieb Thomas Gleixner <tglx@linutronix.de>:
> > > Also can you please try Linus v4.15-rc6 with PTI enabled so we can see
> > > whether that's a backport issue or a general one?
> >
> > Same problem with 4.15-rc6. So I suppose that means it's a general
> > issue.
>
> Just a shot in the dark as I just decoded another issue on a AMD CPU. Can
> you please try the patch below?

Ok. Found the real issue. This is a problem on AMD boxen.

Fix below.

Can Xen folks please have a look at that as well?

Thanks,

tglx

8<-------------------

arch/x86/entry/entry_64_compat.S | 13 ++++++-------
1 file changed, 6 insertions(+), 7 deletions(-)

--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -190,8 +190,13 @@ ENTRY(entry_SYSCALL_compat)
/* Interrupts are off on entry. */
swapgs

- /* Stash user ESP and switch to the kernel stack. */
+ /* Stash user ESP */
movl %esp, %r8d
+
+ /* Use %rsp as scratch reg. User ESP is stashed in r8 */
+ SWITCH_TO_KERNEL_CR3 scratch_reg=%rsp
+
+ /* Switch to the kernel stack */
movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp

/* Construct struct pt_regs on stack */
@@ -220,12 +225,6 @@ GLOBAL(entry_SYSCALL_compat_after_hwfram
pushq $0 /* pt_regs->r15 = 0 */

/*
- * We just saved %rdi so it is safe to clobber. It is not
- * preserved during the C calls inside TRACE_IRQS_OFF anyway.
- */
- SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi
-
- /*
* User mode is traced as though IRQs are on, and SYSENTER
* turned them off.
*/
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