linux-kernel - Re: [PATCH v1] x86/apic: Fix kernel panic when "intremap=off" and "x2apic

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Date:   Mon, 19 Jun 2023 01:24:01 +0300
From:   Cyrill Gorcunov <gorcunov@...il.com>
To:     Dheeraj Kumar Srivastava <dheerajkumar.srivastava@....com>
Cc:     linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org,
        hpa@...or.com, suresh.b.siddha@...el.com,
        Kishon Vijay Abraham I <kvijayab@....com>,
        Vasant Hegde <vasant.hegde@....com>
Subject: Re: [PATCH v1] x86/apic: Fix kernel panic when "intremap=off" and
 "x2apic_phys" are set

On Sat, Jun 17, 2023 at 02:52:36AM +0530, Dheeraj Kumar Srivastava wrote:
> x2APIC mode requires "Interrupt Remapping" to be enabled and the
> "physical x2apic" driver can be used only when x2APIC mode is enabled.
> However when "intremap=off" and "x2apic_phys" kernel command line
> parameters are passed, "physical x2apic" driver is being used even when
> x2APIC mode is disabled ("intremap=off" disables x2APIC mode).
> This results in the below kernel panic:
...

Hi! Good catch! In long term I think we could switch to use x2apic_state variable
instead since at the moment the code is somehow hard to read and remember which exactly
deps are to be satisfied to enable x2apic mode.

Reviewed-by: Cyrill Gorcunov <gorcunov@...il.com>