Commit eed05744 authored by Dongli Zhang's avatar Dongli Zhang Committed by Boris Ostrovsky
Browse files

xen: delay xen_hvm_init_time_ops() if kdump is boot on vcpu>=32 



The sched_clock() can be used very early since commit 857baa87
("sched/clock: Enable sched clock early"). In addition, with commit
38669ba2 ("x86/xen/time: Output xen sched_clock time from 0"), kdump
kernel in Xen HVM guest may panic at very early stage when accessing
&__this_cpu_read(xen_vcpu)->time as in below:

setup_arch()
 -> init_hypervisor_platform()
     -> x86_init.hyper.init_platform = xen_hvm_guest_init()
         -> xen_hvm_init_time_ops()
             -> xen_clocksource_read()
                 -> src = &__this_cpu_read(xen_vcpu)->time;

This is because Xen HVM supports at most MAX_VIRT_CPUS=32 'vcpu_info'
embedded inside 'shared_info' during early stage until xen_vcpu_setup() is
used to allocate/relocate 'vcpu_info' for boot cpu at arbitrary address.

However, when Xen HVM guest panic on vcpu >= 32, since
xen_vcpu_info_reset(0) would set per_cpu(xen_vcpu, cpu) = NULL when
vcpu >= 32, xen_clocksource_read() on vcpu >= 32 would panic.

This patch calls xen_hvm_init_time_ops() again later in
xen_hvm_smp_prepare_boot_cpu() after the 'vcpu_info' for boot vcpu is
registered when the boot vcpu is >= 32.

This issue can be reproduced on purpose via below command at the guest
side when kdump/kexec is enabled:

"taskset -c 33 echo c > /proc/sysrq-trigger"

The bugfix for PVM is not implemented due to the lack of testing
environment.

[boris: xen_hvm_init_time_ops() returns on errors instead of jumping to end]

Cc: Joe Jin <joe.jin@oracle.com>
Signed-off-by: default avatarDongli Zhang <dongli.zhang@oracle.com>
Reviewed-by: default avatarBoris Ostrovsky <boris.ostrovsky@oracle.com>
Link: https://lore.kernel.org/r/20220302164032.14569-3-dongli.zhang@oracle.com


Signed-off-by: default avatarBoris Ostrovsky <boris.ostrovsky@oracle.com>
parent b537bf42

arch/x86/xen/smp_hvm.c

+6 −0
Original line number Original line Diff line number Diff line
@@ -19,6 +19,12 @@ static void __init xen_hvm_smp_prepare_boot_cpu(void) 
	 */

	 */

	xen_vcpu_setup(0);

	xen_vcpu_setup(0);





	/*

	 * Called again in case the kernel boots on vcpu >= MAX_VIRT_CPUS.

	 * Refer to comments in xen_hvm_init_time_ops().

	 */

	xen_hvm_init_time_ops();



	/*

	/*

	 * The alternative logic (which patches the unlock/lock) runs before

	 * The alternative logic (which patches the unlock/lock) runs before

	 * the smp bootup up code is activated. Hence we need to set this up

	 * the smp bootup up code is activated. Hence we need to set this up

arch/x86/xen/time.c

+23 −1
Original line number Original line Diff line number Diff line
@@ -558,6 +558,11 @@ static void xen_hvm_setup_cpu_clockevents(void) 




void __init xen_hvm_init_time_ops(void)

void __init xen_hvm_init_time_ops(void)

{

{

	static bool hvm_time_initialized;



	if (hvm_time_initialized)

		return;



	/*

	/*

	 * vector callback is needed otherwise we cannot receive interrupts

	 * vector callback is needed otherwise we cannot receive interrupts

	 * on cpu > 0 and at this point we don't know how many cpus are

	 * on cpu > 0 and at this point we don't know how many cpus are
@@ -567,7 +572,22 @@ void __init xen_hvm_init_time_ops(void) 
		return;

		return;





	if (!xen_feature(XENFEAT_hvm_safe_pvclock)) {

	if (!xen_feature(XENFEAT_hvm_safe_pvclock)) {

		pr_info("Xen doesn't support pvclock on HVM, disable pv timer");

		pr_info_once("Xen doesn't support pvclock on HVM, disable pv timer");

		return;

	}



	/*

	 * Only MAX_VIRT_CPUS 'vcpu_info' are embedded inside 'shared_info'.

	 * The __this_cpu_read(xen_vcpu) is still NULL when Xen HVM guest

	 * boots on vcpu >= MAX_VIRT_CPUS (e.g., kexec), To access

	 * __this_cpu_read(xen_vcpu) via xen_clocksource_read() will panic.

	 *

	 * The xen_hvm_init_time_ops() should be called again later after

	 * __this_cpu_read(xen_vcpu) is available.

	 */

	if (!__this_cpu_read(xen_vcpu)) {

		pr_info("Delay xen_init_time_common() as kernel is running on vcpu=%d\n",

			xen_vcpu_nr(0));

		return;

		return;

	}

	}
@@ -577,6 +597,8 @@ void __init xen_hvm_init_time_ops(void) 
	x86_cpuinit.setup_percpu_clockev = xen_hvm_setup_cpu_clockevents;

	x86_cpuinit.setup_percpu_clockev = xen_hvm_setup_cpu_clockevents;





	x86_platform.set_wallclock = xen_set_wallclock;

	x86_platform.set_wallclock = xen_set_wallclock;



	hvm_time_initialized = true;

}

}

#endif

#endif