[PATCH 5.15 30/66] x86, kvm: use correct GFP flags for preemption disabled

Greg Kroah-Hartman
2022-06-03T18:02:07Z

From: Paolo Bonzini <pbonzini@redhat.com>

commit baec4f5a018fe2d708fc1022330dba04b38b5fe3 upstream.

Commit ddd7ed842627 ("x86/kvm: Alloc dummy async #PF token outside of
raw spinlock") leads to the following Smatch static checker warning:

arch/x86/kernel/kvm.c:212 kvm_async_pf_task_wake()
warn: sleeping in atomic context

arch/x86/kernel/kvm.c
202 raw_spin_lock(&b->lock);
203 n = _find_apf_task(b, token);
204 if (!n) {
205 /*
206 * Async #PF not yet handled, add a dummy entry for the token.
207 * Allocating the token must be down outside of the raw lock
208 * as the allocator is preemptible on PREEMPT_RT kernels.
209 */
210 if (!dummy) {
211 raw_spin_unlock(&b->lock);
--> 212 dummy = kzalloc(sizeof(*dummy), GFP_KERNEL);
^^^^^^^^^^
Smatch thinks the caller has preempt disabled. The `smdb.py preempt
kvm_async_pf_task_wake` output call tree is:

sysvec_kvm_asyncpf_interrupt() <- disables preempt
-> __sysvec_kvm_asyncpf_interrupt()
-> kvm_async_pf_task_wake()

The caller is this:

arch/x86/kernel/kvm.c
290 DEFINE_IDTENTRY_SYSVEC(sysvec_kvm_asyncpf_interrupt)
291 {
292 struct pt_regs *old_regs = set_irq_regs(regs);
293 u32 token;
294
295 ack_APIC_irq();
296
297 inc_irq_stat(irq_hv_callback_count);
298
299 if (__this_cpu_read(apf_reason.enabled)) {
300 token = __this_cpu_read(apf_reason.token);
301 kvm_async_pf_task_wake(token);
302 __this_cpu_write(apf_reason.token, 0);
303 wrmsrl(MSR_KVM_ASYNC_PF_ACK, 1);
304 }
305
306 set_irq_regs(old_regs);
307 }

The DEFINE_IDTENTRY_SYSVEC() is a wrapper that calls this function
from the call_on_irqstack_cond(). It's inside the call_on_irqstack_cond()
where preempt is disabled (unless it's already disabled). The
irq_enter/exit_rcu() functions disable/enable preempt.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/kernel/kvm.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -206,7 +206,7 @@ again:
*/
if (!dummy) {
raw_spin_unlock(&b->lock);
- dummy = kzalloc(sizeof(*dummy), GFP_KERNEL);
+ dummy = kzalloc(sizeof(*dummy), GFP_ATOMIC);

/*
* Continue looping on allocation failure, eventually