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Message-ID: <20250930103130.197534-2-suzuki.poulose@arm.com>
Date: Tue, 30 Sep 2025 11:31:15 +0100
From: Suzuki K Poulose <suzuki.poulose@....com>
To: kvmarm@...ts.linux.dev
Cc: kvm@...r.kernel.org,
linux-kernel@...r.kernel.org,
will@...nel.org,
oliver.upton@...ux.dev,
maz@...nel.org,
alexandru.elisei@....com,
aneesh.kumar@...nel.org,
steven.price@....com,
tabba@...gle.com,
Suzuki K Poulose <suzuki.poulose@....com>
Subject: [PATCH kvmtool v4 01/15] Allow pausing the VM from vcpu thread
Pausing the VM from a vCPU thread doesn't work today, as it waits indefinitely
for a signal that never comes. By using the "current_kvm_cpu", enlighten the
kvm__pause() to skip the current CPU and do it inline. This also brings in a
restriction that a following kvm__continue() must be called from the same vCPU
thread.
Cc: Will Deacon <will@...nel.org>
Cc: Oliver Upton <oliver.upton@...ux.dev>
Link: https://lore.kernel.org/all/20230918104028.GA17744@willie-the-truck/
Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
---
kvm.c | 35 +++++++++++++++++++++++++++++++----
1 file changed, 31 insertions(+), 4 deletions(-)
diff --git a/kvm.c b/kvm.c
index 07089cf1..cc25ecdb 100644
--- a/kvm.c
+++ b/kvm.c
@@ -59,6 +59,8 @@ const char *kvm_exit_reasons[] = {
static int pause_event;
static DEFINE_MUTEX(pause_lock);
+static struct kvm_cpu *pause_req_cpu;
+
extern struct kvm_ext kvm_req_ext[];
static char kvm_dir[PATH_MAX];
@@ -573,9 +575,25 @@ void kvm__reboot(struct kvm *kvm)
void kvm__continue(struct kvm *kvm)
{
+ /*
+ * We must ensure that the resume request comes from the same context
+ * as the one requested the pause, especially if it was issued from a
+ * vCPU thread.
+ */
+ if (current_kvm_cpu) {
+ if (pause_req_cpu != current_kvm_cpu ||
+ !current_kvm_cpu->paused)
+ die("Trying to resume VM from invalid context");
+ current_kvm_cpu->paused = 0;
+ }
mutex_unlock(&pause_lock);
}
+/*
+ * Mark all active CPUs as paused, until kvm__continue() is issued.
+ * NOTE: If this is called from a cpu thread, kvm__continue() must
+ * be called from the same thread.
+ */
void kvm__pause(struct kvm *kvm)
{
int i, paused_vcpus = 0;
@@ -590,10 +608,17 @@ void kvm__pause(struct kvm *kvm)
if (pause_event < 0)
die("Failed creating pause notification event");
for (i = 0; i < kvm->nrcpus; i++) {
- if (kvm->cpus[i]->is_running && kvm->cpus[i]->paused == 0)
- pthread_kill(kvm->cpus[i]->thread, SIGKVMPAUSE);
- else
- paused_vcpus++;
+ if (kvm->cpus[i]->is_running && kvm->cpus[i]->paused == 0) {
+ if (current_kvm_cpu != kvm->cpus[i]) {
+ pthread_kill(kvm->cpus[i]->thread, SIGKVMPAUSE);
+ continue;
+ } else if (current_kvm_cpu) {
+ current_kvm_cpu->paused = 1;
+ pause_req_cpu = current_kvm_cpu;
+ /* fall through to update our count */
+ }
+ }
+ paused_vcpus++;
}
while (paused_vcpus < kvm->nrcpus) {
@@ -604,6 +629,8 @@ void kvm__pause(struct kvm *kvm)
paused_vcpus += cur_read;
}
close(pause_event);
+ /* Remember the context requesting pause */
+ pause_req_cpu = current_kvm_cpu;
}
void kvm__notify_paused(void)
--
2.43.0
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