On Wed, Jan 3, 2018 at 10:52 AM, Thomas Gleixner <t...@linutronix.de> wrote: > 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 <t...@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. > */
What's the issue that this is fixing?
