[PATCH] xen: fix is_xen_pmu()

[PATCH] xen: fix is_xen_pmu()

[Juergen Gross]

is_xen_pmu() is taking the cpu number as parameter, but it is not using
it. Instead it just tests whether the Xen PMU initialization on the
current cpu did succeed. As this test is done by checking a percpu
pointer, preemption needs to be disabled in order to avoid switching
the cpu while doing the test. While resuming from suspend() this seems
not to be the case:

[   88.082751] ACPI: PM: Low-level resume complete
[   88.087933] ACPI: EC: EC started
[   88.091464] ACPI: PM: Restoring platform NVS memory
[   88.097166] xen_acpi_processor: Uploading Xen processor PM info
[   88.103850] Enabling non-boot CPUs ...
[   88.108128] installing Xen timer for CPU 1
[   88.112763] BUG: using smp_processor_id() in preemptible [00000000] code: systemd-sleep/7138
[   88.122256] caller is is_xen_pmu+0x12/0x30
[   88.126937] CPU: 0 PID: 7138 Comm: systemd-sleep Tainted: G        W         5.16.13-2.fc32.qubes.x86_64 #1
[   88.137939] Hardware name: Star Labs StarBook/StarBook, BIOS 7.97 03/21/2022
[   88.145930] Call Trace:
[   88.148757]  <TASK>
[   88.151193]  dump_stack_lvl+0x48/0x5e
[   88.155381]  check_preemption_disabled+0xde/0xe0
[   88.160641]  is_xen_pmu+0x12/0x30
[   88.164441]  xen_smp_intr_init_pv+0x75/0x100

Fix that by replacing is_xen_pmu() by a simple boolean variable which
reflects the Xen PMU initialization state on cpu 0.

Modify xen_pmu_init() to return early in case it is being called for a
cpu other than cpu 0 and the boolean variable not being set.

Fixes: bf6dfb154d93 ("xen/PMU: PMU emulation code")
Reported-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
---
 arch/x86/xen/pmu.c    | 11 ++++++-----
 arch/x86/xen/pmu.h    |  3 ++-
 arch/x86/xen/smp_pv.c |  2 +-
 3 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/arch/x86/xen/pmu.c b/arch/x86/xen/pmu.c
index 89dd6b1708b0..0efe452eb13e 100644
--- a/arch/x86/xen/pmu.c
+++ b/arch/x86/xen/pmu.c
@@ -506,10 +506,7 @@ irqreturn_t xen_pmu_irq_handler(int irq, void *dev_id)
 	return ret;
 }
 
-bool is_xen_pmu(int cpu)
-{
-	return (get_xenpmu_data() != NULL);
-}
+bool is_xen_pmu;
 
 void xen_pmu_init(int cpu)
 {
@@ -520,7 +517,7 @@ void xen_pmu_init(int cpu)
 
 	BUILD_BUG_ON(sizeof(struct xen_pmu_data) > PAGE_SIZE);
 
-	if (xen_hvm_domain())
+	if (xen_hvm_domain() || (cpu != 0 && !is_xen_pmu))
 		return;
 
 	xenpmu_data = (struct xen_pmu_data *)get_zeroed_page(GFP_KERNEL);
@@ -542,6 +539,7 @@ void xen_pmu_init(int cpu)
 	per_cpu(xenpmu_shared, cpu).flags = 0;
 
 	if (cpu == 0) {
+		is_xen_pmu = true;
 		perf_register_guest_info_callbacks(&xen_guest_cbs);
 		xen_pmu_arch_init();
 	}
@@ -572,4 +570,7 @@ void xen_pmu_finish(int cpu)
 
 	free_pages((unsigned long)per_cpu(xenpmu_shared, cpu).xenpmu_data, 0);
 	per_cpu(xenpmu_shared, cpu).xenpmu_data = NULL;
+
+	if (cpu == 0)
+		is_xen_pmu = false;
 }
diff --git a/arch/x86/xen/pmu.h b/arch/x86/xen/pmu.h
index 0e83a160589b..65c58894fc79 100644
--- a/arch/x86/xen/pmu.h
+++ b/arch/x86/xen/pmu.h
@@ -4,6 +4,8 @@
 
 #include <xen/interface/xenpmu.h>
 
+extern bool is_xen_pmu;
+
 irqreturn_t xen_pmu_irq_handler(int irq, void *dev_id);
 #ifdef CONFIG_XEN_HAVE_VPMU
 void xen_pmu_init(int cpu);
@@ -12,7 +14,6 @@ void xen_pmu_finish(int cpu);
 static inline void xen_pmu_init(int cpu) {}
 static inline void xen_pmu_finish(int cpu) {}
 #endif
-bool is_xen_pmu(int cpu);
 bool pmu_msr_read(unsigned int msr, uint64_t *val, int *err);
 bool pmu_msr_write(unsigned int msr, uint32_t low, uint32_t high, int *err);
 int pmu_apic_update(uint32_t reg);
diff --git a/arch/x86/xen/smp_pv.c b/arch/x86/xen/smp_pv.c
index 4a6019238ee7..688aa8b6ae29 100644
--- a/arch/x86/xen/smp_pv.c
+++ b/arch/x86/xen/smp_pv.c
@@ -129,7 +129,7 @@ int xen_smp_intr_init_pv(unsigned int cpu)
 	per_cpu(xen_irq_work, cpu).irq = rc;
 	per_cpu(xen_irq_work, cpu).name = callfunc_name;
 
-	if (is_xen_pmu(cpu)) {
+	if (is_xen_pmu) {
 		pmu_name = kasprintf(GFP_KERNEL, "pmu%d", cpu);
 		rc = bind_virq_to_irqhandler(VIRQ_XENPMU, cpu,
 					     xen_pmu_irq_handler,
-- 
2.34.1

Re: [PATCH] xen: fix is_xen_pmu()

[Boris Ostrovsky]

On 3/22/22 11:50 AM, Juergen Gross wrote:
> is_xen_pmu() is taking the cpu number as parameter, but it is not using
> it. Instead it just tests whether the Xen PMU initialization on the
> current cpu did succeed. As this test is done by checking a percpu
> pointer, preemption needs to be disabled in order to avoid switching
> the cpu while doing the test. While resuming from suspend() this seems
> not to be the case:
>
> [   88.082751] ACPI: PM: Low-level resume complete
> [   88.087933] ACPI: EC: EC started
> [   88.091464] ACPI: PM: Restoring platform NVS memory
> [   88.097166] xen_acpi_processor: Uploading Xen processor PM info
> [   88.103850] Enabling non-boot CPUs ...
> [   88.108128] installing Xen timer for CPU 1
> [   88.112763] BUG: using smp_processor_id() in preemptible [00000000] code: systemd-sleep/7138
> [   88.122256] caller is is_xen_pmu+0x12/0x30
> [   88.126937] CPU: 0 PID: 7138 Comm: systemd-sleep Tainted: G        W         5.16.13-2.fc32.qubes.x86_64 #1
> [   88.137939] Hardware name: Star Labs StarBook/StarBook, BIOS 7.97 03/21/2022
> [   88.145930] Call Trace:
> [   88.148757]  <TASK>
> [   88.151193]  dump_stack_lvl+0x48/0x5e
> [   88.155381]  check_preemption_disabled+0xde/0xe0
> [   88.160641]  is_xen_pmu+0x12/0x30
> [   88.164441]  xen_smp_intr_init_pv+0x75/0x100


There is actually another PMU-related problem on restore which was caused (or, rather, highlighted) by ff083a2d972f56bebfd82409ca62e5dfce950961:


[  116.861637] ------------[ cut here ]------------
[  116.861651] WARNING: CPU: 1 PID: 31 at kernel/events/core.c:6614 perf_register_guest_info_callbacks+0x68/0x70
[  116.861673] Modules linked in:
[  116.861682] CPU: 1 PID: 31 Comm: xenwatch Not tainted 5.17.0-rc7ostr #103
[  116.861695] RIP: e030:perf_register_guest_info_callbacks+0x68/0x70
[  116.861706] Code: c7 c7 40 e1 86 82 e8 d7 e7 ff ff 48 8b 53 10 48 85 d2 74 14 48 c7 c6 f0 0a c0 81 48 c7 c7 30 e1 86 82 5b e9 ba e7 ff ff 5b c3 <0f> 0b c3 0f 1f 44 00 00 0f 1f 44 00 00 48 8b 05 54 fd 0b 02 48 39
[  116.861747] RSP: e02b:ffffc9004016fe18 EFLAGS: 00010286
[  116.861758] RAX: ffffffff82432850 RBX: 0000000000000003 RCX: ffff888079c00000
[  116.861768] RDX: ffff888079c00000 RSI: ffffc9004016fe30 RDI: ffffffff82432850
[  116.861778] RBP: 0000000000000000 R08: 0000160000000000 R09: ffffea00000ed340
[  116.861788] R10: 0000000000000758 R11: 0000000000000000 R12: ffff888003b4d000
[  116.861797] R13: 0000000000000003 R14: ffffffff8162cf10 R15: 0000000000000000
[  116.861819] FS:  0000000000000000(0000) GS:ffff888079c80000(0000) knlGS:0000000000000000
[  116.861830] CS:  e030 DS: 0000 ES: 0000 CR0: 0000000080050033
[  116.861839] CR2: 0000000000000000 CR3: 00000000062b6000 CR4: 0000000000040660
[  116.861853] Call Trace:
[  116.861861]  <TASK>
[  116.861866]  xen_pmu_init+0x187/0x280
[  116.861879]  xen_arch_resume+0x30/0x50
[  116.861888]  do_suspend.cold+0x132/0x147
[  116.861899]  shutdown_handler+0x12e/0x140
[  116.861910]  xenwatch_thread+0x94/0x180
[  116.861919]  ? finish_wait+0x80/0x80
[  116.861928]  kthread+0xe7/0x110
[  116.861938]  ? kthread_complete_and_exit+0x20/0x20
[  116.861948]  ret_from_fork+0x22/0x30
[  116.861959]  </TASK>
[  116.861964] ---[ end trace 0000000000000000 ]---


I was going to send a patch but I think yours can be slightly modified to take care of this problem as well.



> @@ -542,6 +539,7 @@ void xen_pmu_init(int cpu)
>   	per_cpu(xenpmu_shared, cpu).flags = 0;
>   
>   	if (cpu == 0) {


               if (!is_xen_pmu)


> +		is_xen_pmu = true;
>   		perf_register_guest_info_callbacks(&xen_guest_cbs);
>   		xen_pmu_arch_init();
>   	}
> @@ -572,4 +570,7 @@ void xen_pmu_finish(int cpu)
>   
>   	free_pages((unsigned long)per_cpu(xenpmu_shared, cpu).xenpmu_data, 0);
>   	per_cpu(xenpmu_shared, cpu).xenpmu_data = NULL;
> +
> +	if (cpu == 0)
> +		is_xen_pmu = false;


And drop this hunk.


-boris