[PATCH AUTOSEL 5.10 26/45] x86/xen: Fix xen_hvm_smp_init() when vector callback not available

From: Sasha Levin
Date: Tue Jan 19 2021 - 22:22:00 EST

From: David Woodhouse <dwmw@xxxxxxxxxxxx>

[ Upstream commit 3d7746bea92530e8695258a3cf3ddec7a135edd6 ]

Only the IPI-related functions in the smp_ops should be conditional
on the vector callback being available. The rest should still happen:

• xen_hvm_smp_prepare_boot_cpu()

This function does two things, both of which should still happen if
there is no vector callback support.

The call to xen_vcpu_setup() for vCPU0 should still happen as it just
sets up the vcpu_info for CPU0. That does happen for the secondary
vCPUs too, from xen_cpu_up_prepare_hvm().

The second thing it does is call xen_init_spinlocks(), which perhaps
counter-intuitively should *also* still be happening in the case
without vector callbacks, so that it can clear its local xen_pvspin
flag and disable the virt_spin_lock_key accordingly.

Checking xen_have_vector_callback in xen_init_spinlocks() itself
would affect PV guests, so set the global nopvspin flag in
xen_hvm_smp_init() instead, when vector callbacks aren't available.

• xen_hvm_smp_prepare_cpus()

This does some IPI-related setup by calling xen_smp_intr_init() and
xen_init_lock_cpu(), which can be made conditional. And it sets the
xen_vcpu_id to XEN_VCPU_ID_INVALID for all possible CPUS, which does
need to happen.

• xen_smp_cpus_done()

This offlines any vCPUs which doesn't fit in the global shared_info
page, if separate vcpu_info placement isn't available. That part also
needs to happen regardless of vector callback support.

• xen_hvm_cpu_die()

This doesn't actually do anything other than commin_cpu_die() right
right now in the !vector_callback case; all three teardown functions
it calls should be no-ops. But to guard against future regressions
it's useful to call it anyway, and for it to explicitly check for
xen_have_vector_callback before calling those additional functions.

Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20210106153958.584169-6-dwmw2@xxxxxxxxxxxxx
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
arch/x86/xen/smp_hvm.c | 27 +++++++++++++++++----------
1 file changed, 17 insertions(+), 10 deletions(-)

diff --git a/arch/x86/xen/smp_hvm.c b/arch/x86/xen/smp_hvm.c
index f5e7db4f82abb..056430a1080bb 100644
--- a/arch/x86/xen/smp_hvm.c
+++ b/arch/x86/xen/smp_hvm.c
@@ -33,9 +33,11 @@ static void __init xen_hvm_smp_prepare_cpus(unsigned int max_cpus)
int cpu;

- WARN_ON(xen_smp_intr_init(0));

- xen_init_lock_cpu(0);
+ if (xen_have_vector_callback) {
+ WARN_ON(xen_smp_intr_init(0));
+ xen_init_lock_cpu(0);
+ }

for_each_possible_cpu(cpu) {
if (cpu == 0)
@@ -50,9 +52,11 @@ static void __init xen_hvm_smp_prepare_cpus(unsigned int max_cpus)
static void xen_hvm_cpu_die(unsigned int cpu)
if (common_cpu_die(cpu) == 0) {
- xen_smp_intr_free(cpu);
- xen_uninit_lock_cpu(cpu);
- xen_teardown_timer(cpu);
+ if (xen_have_vector_callback) {
+ xen_smp_intr_free(cpu);
+ xen_uninit_lock_cpu(cpu);
+ xen_teardown_timer(cpu);
+ }
@@ -64,14 +68,17 @@ static void xen_hvm_cpu_die(unsigned int cpu)

void __init xen_hvm_smp_init(void)
- if (!xen_have_vector_callback)
+ smp_ops.smp_prepare_boot_cpu = xen_hvm_smp_prepare_boot_cpu;
+ smp_ops.smp_prepare_cpus = xen_hvm_smp_prepare_cpus;
+ smp_ops.smp_cpus_done = xen_smp_cpus_done;
+ smp_ops.cpu_die = xen_hvm_cpu_die;
+ if (!xen_have_vector_callback) {
+ nopvspin = true;
+ }

- smp_ops.smp_prepare_cpus = xen_hvm_smp_prepare_cpus;
smp_ops.smp_send_reschedule = xen_smp_send_reschedule;
- smp_ops.cpu_die = xen_hvm_cpu_die;
smp_ops.send_call_func_ipi = xen_smp_send_call_function_ipi;
smp_ops.send_call_func_single_ipi = xen_smp_send_call_function_single_ipi;
- smp_ops.smp_prepare_boot_cpu = xen_hvm_smp_prepare_boot_cpu;
- smp_ops.smp_cpus_done = xen_smp_cpus_done;