This is a note to let you know that I've just added the patch titled
KVM: arm64: Disable preemption in kvm_arch_hardware_enable()
to the 6.4-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:
kvm-arm64-disable-preemption-in-kvm_arch_hardware_enable.patch
and it can be found in the queue-6.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 970dee09b230895fe2230d2b32ad05a2826818c6 Mon Sep 17 00:00:00 2001
From: Marc Zyngier <maz@xxxxxxxxxx>
Date: Mon, 3 Jul 2023 17:35:48 +0100
Subject: KVM: arm64: Disable preemption in kvm_arch_hardware_enable()
From: Marc Zyngier <maz@xxxxxxxxxx>
commit 970dee09b230895fe2230d2b32ad05a2826818c6 upstream.
Since 0bf50497f03b ("KVM: Drop kvm_count_lock and instead protect
kvm_usage_count with kvm_lock"), hotplugging back a CPU whilst
a guest is running results in a number of ugly splats as most
of this code expects to run with preemption disabled, which isn't
the case anymore.
While the context is preemptable, it isn't migratable, which should
be enough. But we have plenty of preemptible() checks all over
the place, and our per-CPU accessors also disable preemption.
Since this affects released versions, let's do the easy fix first,
disabling preemption in kvm_arch_hardware_enable(). We can always
revisit this with a more invasive fix in the future.
Fixes: 0bf50497f03b ("KVM: Drop kvm_count_lock and instead protect kvm_usage_count with kvm_lock")
Reported-by: Kristina Martsenko <kristina.martsenko@xxxxxxx>
Tested-by: Kristina Martsenko <kristina.martsenko@xxxxxxx>
Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
Link: https://lore.kernel.org/r/aeab7562-2d39-e78e-93b1-4711f8cc3fa5@xxxxxxx
Cc: stable@xxxxxxxxxxxxxxx # v6.3, v6.4
Link: https://lore.kernel.org/r/20230703163548.1498943-1-maz@xxxxxxxxxx
Signed-off-by: Oliver Upton <oliver.upton@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/arm64/kvm/arm.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -1793,8 +1793,17 @@ static void _kvm_arch_hardware_enable(vo
int kvm_arch_hardware_enable(void)
{
- int was_enabled = __this_cpu_read(kvm_arm_hardware_enabled);
+ int was_enabled;
+ /*
+ * Most calls to this function are made with migration
+ * disabled, but not with preemption disabled. The former is
+ * enough to ensure correctness, but most of the helpers
+ * expect the later and will throw a tantrum otherwise.
+ */
+ preempt_disable();
+
+ was_enabled = __this_cpu_read(kvm_arm_hardware_enabled);
_kvm_arch_hardware_enable(NULL);
if (!was_enabled) {
@@ -1802,6 +1811,8 @@ int kvm_arch_hardware_enable(void)
kvm_timer_cpu_up();
}
+ preempt_enable();
+
return 0;
}
Patches currently in stable-queue which might be from maz@xxxxxxxxxx are
queue-6.4/kvm-arm64-timers-use-cnthctl_el2-when-setting-non-cntkctl_el1-bits.patch
queue-6.4/kvm-arm64-disable-preemption-in-kvm_arch_hardware_enable.patch
queue-6.4/kvm-arm64-correctly-handle-page-aging-notifiers-for-unaligned-memslot.patch
queue-6.4/kvm-arm64-vgic-v4-make-the-doorbell-request-robust-w.r.t-preemption.patch
