linux-kernel - Re: [PATCH] xen: fix is_xen

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Message-ID: <bf8a41ed-3d93-9f60-5e2d-780abc177325@oracle.com>
Date:   Tue, 22 Mar 2022 16:00:43 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Juergen Gross <jgross@...e.com>, xen-devel@...ts.xenproject.org,
        x86@...nel.org, linux-kernel@...r.kernel.org
Cc:     Stefano Stabellini <sstabellini@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Marek Marczykowski-Górecki 
        <marmarek@...isiblethingslab.com>
Subject: Re: [PATCH] xen: fix is_xen_pmu()


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