linux-kernel - Re: [PATCH v2] xen: fix is_xen

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Date:   Fri, 25 Mar 2022 15:18:52 -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 v2] xen: fix is_xen_pmu()


On 3/25/22 10:20 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
>
> 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@...isiblethingslab.com>
> Signed-off-by: Juergen Gross <jgross@...e.com>


Reviewed-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>