This is a note to let you know that I've just added the patch titled x86/xen: Make the boot CPU idle task reliable to the 5.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: x86-xen-make-the-boot-cpu-idle-task-reliable.patch and it can be found in the queue-5.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 2f62f36e62daec43aa7b9633ef7f18e042a80bed Mon Sep 17 00:00:00 2001 From: Miroslav Benes <mbenes@xxxxxxx> Date: Thu, 26 Mar 2020 10:26:02 +0100 Subject: x86/xen: Make the boot CPU idle task reliable From: Miroslav Benes <mbenes@xxxxxxx> commit 2f62f36e62daec43aa7b9633ef7f18e042a80bed upstream. The unwinder reports the boot CPU idle task's stack on XEN PV as unreliable, which affects at least live patching. There are two reasons for this. First, the task does not follow the x86 convention that its stack starts at the offset right below saved pt_regs. It allows the unwinder to easily detect the end of the stack and verify it. Second, startup_xen() function does not store the return address before jumping to xen_start_kernel() which confuses the unwinder. Amend both issues by moving the starting point of initial stack in startup_xen() and storing the return address before the jump, which is exactly what call instruction does. Signed-off-by: Miroslav Benes <mbenes@xxxxxxx> Reviewed-by: Juergen Gross <jgross@xxxxxxxx> Signed-off-by: Juergen Gross <jgross@xxxxxxxx> Signed-off-by: Markus Boehme <markubo@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/x86/xen/xen-head.S | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) --- a/arch/x86/xen/xen-head.S +++ b/arch/x86/xen/xen-head.S @@ -35,7 +35,11 @@ ENTRY(startup_xen) rep __ASM_SIZE(stos) mov %_ASM_SI, xen_start_info - mov $init_thread_union+THREAD_SIZE, %_ASM_SP +#ifdef CONFIG_X86_64 + mov initial_stack(%rip), %rsp +#else + mov pa(initial_stack), %esp +#endif #ifdef CONFIG_X86_64 /* Set up %gs. @@ -51,7 +55,7 @@ ENTRY(startup_xen) wrmsr #endif - jmp xen_start_kernel + call xen_start_kernel END(startup_xen) __FINIT #endif Patches currently in stable-queue which might be from mbenes@xxxxxxx are queue-5.4/x86-xen-make-the-boot-cpu-idle-task-reliable.patch queue-5.4/x86-xen-make-the-secondary-cpu-idle-tasks-reliable.patch