linux-kernel - Re: [PATCH v3] platform/x86: don't unconditionally attach Intel PMC when virtualized

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Message-ID: <8f28a8dd-5a0c-c233-217c-0e610b830406@redhat.com>
Date:   Tue, 15 Nov 2022 16:55:40 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Roger Pau Monne <roger.pau@...rix.com>,
        linux-kernel@...r.kernel.org
Cc:     xen-devel@...ts.xenproject.org, jgross@...e.com,
        "David E . Box" <david.e.box@...ux.intel.com>,
        Rajneesh Bhardwaj <irenic.rajneesh@...il.com>,
        David E Box <david.e.box@...el.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 v3] platform/x86: don't unconditionally attach Intel PMC
 when virtualized

Hi,

On 11/10/22 17:31, 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>
> Acked-by: David E. Box <david.e.box@...ux.intel.com>

Thank you for your patch, I've applied this patch to my fixes
branch:
https://git.kernel.org/pub/scm/linux/kernel/git/pdx86/platform-drivers-x86.git/log/?h=fixes

Note it will show up in my fixes branch once I've pushed my
local branch there, which might take a while.

I will include this patch in my next fixes pull-req to Linus
for the current kernel development cycle.

Regards,

Hans



> ---
> Changes since v2:
>  - Don't split condition line.
> 
> Changes since v1:
>  - Use cpu_feature_enabled() instead of boot_cpu_has().
> ---
>  drivers/platform/x86/intel/pmc/pltdrv.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/platform/x86/intel/pmc/pltdrv.c b/drivers/platform/x86/intel/pmc/pltdrv.c
> index 15ca8afdd973..ddfba38c2104 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 +55,13 @@ 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 (cpu_feature_enabled(X86_FEATURE_HYPERVISOR) && !xen_initial_domain())
> +		return -ENODEV;
> +
>  	if (!x86_match_cpu(intel_pmc_core_platform_ids))
>  		return -ENODEV;
>