linux-kernel - Re: [PATCH v2] platform/x86: don't unconditionally attach Intel PMC when virtualized

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Message-ID: <Y20IjBPSXE+kqOZS@smile.fi.intel.com>
Date:   Thu, 10 Nov 2022 16:19:56 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Roger Pau Monne <roger.pau@...rix.com>
Cc:     linux-kernel@...r.kernel.org,
        "David E . Box" <david.e.box@...ux.intel.com>,
        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>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Juergen Gross <jgross@...e.com>,
        platform-driver-x86@...r.kernel.org, xen-devel@...ts.xenproject.org
Subject: Re: [PATCH v2] platform/x86: don't unconditionally attach Intel PMC
 when virtualized

On Thu, Nov 10, 2022 at 02:33:35PM +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.
> 
> 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>

> 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: Juergen Gross <jgross@...e.com>
> Cc: platform-driver-x86@...r.kernel.org
> Cc: xen-devel@...ts.xenproject.org

You may use --cc to the sending tool, instead of polluting a commit message
with that. Moreover, the Cc list will be archived on lore.kernel.org anyway,
in case you really need it to be recorded.

...

> +	if (cpu_feature_enabled(X86_FEATURE_HYPERVISOR) &&
> +	    !xen_initial_domain())

One line? It's 81 character only and we have no strong 80 here, IIRC.

> +		return -ENODEV;

-- 
With Best Regards,
Andy Shevchenko