linux-kernel - Re: [PATCH] platform/x86: don't unconditionally attach Intel PMC when virtualized

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Message-ID: <4367a7a8-e6b8-bebe-b2df-0294a755dec8@suse.com>
Date:   Wed, 9 Nov 2022 16:24:48 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Roger Pau Monne <roger.pau@...rix.com>,
        linux-kernel@...r.kernel.org
Cc:     Rajneesh Bhardwaj <irenic.rajneesh@...il.com>,
        David E Box <david.e.box@...el.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Mark Gross <markgross@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        platform-driver-x86@...r.kernel.org
Subject: Re: [PATCH] platform/x86: don't unconditionally attach Intel PMC when
 virtualized

On 09.11.22 16:16, Roger Pau Monne wrote:
> The current logic in the Intel PMC driver will forcefully attach it
> when detecting any CPU on the intel_pmc_core_platform_ids array,
> even if the matching ACPI device is not present.
> 
> There's no checking in pmc_core_probe() to assert that the PMC device
> is present, and hence on virtualized environments the PMC device
> probes successfully, even if the underlying registers are not present.
> Previous to 21ae43570940 the driver would check for the presence of a
> specific PCI device, and that prevented the driver from attaching when
> running virtualized.
> 
> Fix by only forcefully attaching the PMC device when not running
> virtualized.  Note that virtualized platforms can still get the device
> to load if the appropriate ACPI device is present on the tables
> provided to the VM.
> 
> Make an exception for the Xen initial domain, which does have full
> hardware access, and hence can attach to the PMC if present.
> 
> Fixes: 21ae43570940 ('platform/x86: intel_pmc_core: Substitute PCI with CPUID enumeration')
> Signed-off-by: Roger Pau Monné <roger.pau@...rix.com>
> Cc: Rajneesh Bhardwaj <irenic.rajneesh@...il.com>
> Cc: David E Box <david.e.box@...el.com>
> Cc: Hans de Goede <hdegoede@...hat.com>
> Cc: Mark Gross <markgross@...nel.org>
> Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Cc: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
> Cc: platform-driver-x86@...r.kernel.org
> ---
>   drivers/platform/x86/intel/pmc/pltdrv.c | 10 ++++++++++
>   1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/platform/x86/intel/pmc/pltdrv.c b/drivers/platform/x86/intel/pmc/pltdrv.c
> index 15ca8afdd973..e284fd34ffdf 100644
> --- a/drivers/platform/x86/intel/pmc/pltdrv.c
> +++ b/drivers/platform/x86/intel/pmc/pltdrv.c
> @@ -18,6 +18,8 @@
>   #include <asm/cpu_device_id.h>
>   #include <asm/intel-family.h>
>   
> +#include <xen/xen.h>
> +
>   static void intel_pmc_core_release(struct device *dev)
>   {
>   	kfree(dev);
> @@ -53,6 +55,14 @@ static int __init pmc_core_platform_init(void)
>   	if (acpi_dev_present("INT33A1", NULL, -1))
>   		return -ENODEV;
>   
> +	/*
> +	 * Skip forcefully attaching the device for VMs. Make an exception for
> +	 * Xen dom0, which does have full hardware access.
> +	 */
> +	if (boot_cpu_has(X86_FEATURE_HYPERVISOR) &&

Please use cpu_feature_enabled() instead of boot_cpu_has().


Juergen

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