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

[Andy Shevchenko]

On Thu, Nov 10, 2022 at 05:31:44PM +0100, 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.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>

> Fixes: 21ae43570940 ('platform/x86: intel_pmc_core: Substitute PCI with CPUID enumeration')
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> Acked-by: David E. Box <david.e.box@xxxxxxxxxxxxxxx>
> ---
> 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;
>  
> -- 
> 2.37.3
> 

-- 
With Best Regards,
Andy Shevchenko