On 06/12/17 07:00, Andy Lutomirski wrote:
> Add to commit message:
>
> Using a trampoline stack would obnoxious for Xen PV because Xen PV
> enters entry_SYSCALL_64_after_hwframe on the stack indicated by sp0.
> This could be fixed, but I think it's nice to ensure the entry code
> can still work without a trampoline stack. So this patch doesn't
> use the entry trampoline stack on Xen.
>
> The regs != eregs check in sync_regs is optional, but I think it's
> better than copying the whole set of regs over itself.
>
> Signed-off-by: Andy Lutomirski <l...@kernel.org>
I verified the crash occurring without the patch when started as a
pv guest.
Your patch makes pv guest boot again. HVM guest is working, too.
You can add my:
Tested-by: Juergen Gross <jgr...@suse.com>
Juergen
> ---
>
> Boris, this is lightly tested and should fix the problem you're seeing.
>
> arch/x86/include/asm/switch_to.h | 3 +++
> arch/x86/kernel/traps.c | 9 +++++----
> 2 files changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/include/asm/switch_to.h
> b/arch/x86/include/asm/switch_to.h
> index fab453ad2460..cbc71e73bd32 100644
> --- a/arch/x86/include/asm/switch_to.h
> +++ b/arch/x86/include/asm/switch_to.h
> @@ -93,6 +93,9 @@ static inline void update_sp0(struct task_struct *task)
> /* On x86_64, sp0 always points to the entry trampoline stack, which is
> constant: */
> #ifdef CONFIG_X86_32
> load_sp0(task->thread.sp0);
> +#else
> + if (static_cpu_has(X86_FEATURE_XENPV))
> + load_sp0(task_top_of_stack(task));
> #endif
> }
>
> diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
> index 40cc3dc5967a..ee9ca0ad4388 100644
> --- a/arch/x86/kernel/traps.c
> +++ b/arch/x86/kernel/traps.c
> @@ -619,14 +619,15 @@ NOKPROBE_SYMBOL(do_int3);
>
> #ifdef CONFIG_X86_64
> /*
> - * Help handler running on IST stack to switch off the IST stack if the
> - * interrupted code was in user mode. The actual stack switch is done in
> - * entry_64.S
> + * Help handler running on a per-cpu (IST or entry trampoline) stack
> + * to switch to the normal thread stack if the interrupted code was in
> + * user mode. The actual stack switch is done in entry_64.S
> */
> asmlinkage __visible notrace struct pt_regs *sync_regs(struct pt_regs *eregs)
> {
> struct pt_regs *regs = (struct pt_regs
> *)this_cpu_read(cpu_current_top_of_stack) - 1;
> - *regs = *eregs;
> + if (regs != eregs)
> + *regs = *eregs;
> return regs;
> }
> NOKPROBE_SYMBOL(sync_regs);
>
